There are occasionally times that large dust specs very near the rear element are visible in an image, though. There also is the very real issue of resale value; a dusty lens tends to bring a lower price than one without much dust. The right answer in these cases is “send it in for factory service, they’ll disassemble it and clean it.” Doing it yourself is risky.

After I give all of those answers, a lot of people tell me they have an old lens no longer under warranty, not worth the cost of sending it in for factory cleaning, and they are really handy and want to do it themselves. For those people, we’ve put up this post showing how to get dust out of some fairly easy to reach locations.

More Than the Usual Warnings Apply

1. If you open a lens you have completely voided the warranty. Don’t do this on any lens still in warranty.
2. You can change a dusty lens into an unusable lens if things go wrong. And things do go wrong.
3. If you mess up and strip a screw or tear a flex, factory service may (or may not) even attempt to repair it. If they do decide to repair it they will charge an additional “tampered with” fee in addition to the service charge. It is reasonable for them to do so. It’s way harder and more time consuming to repair a lens someone has messed up.
4. If things go really wrong and you can’t reassemble the lens, nobody, and I mean nobody, will put it back together for you at any price. I get asked to do it occasionally, and I won’t even consider it. It’s one thing to reassemble a lens I’ve carefully disassembled, keeping the parts organized. It’s another to try to put together a 3 dimensional jigsaw puzzle of pieces.
5. Chances are you really don’t need to do this anyway. Even a moderate amount of dust rarely has any effect on images.

Now, if you’ve read all of those warnings, have an appropriately old, out of warranty lens, and are certain the dust needs to be removed (even though it probably doesn’t), read on.

Tools Needed

You’ll need a good quality, J. I. S. (Japanese Industrial Standard) #00 or #000 screwdriver. Lens screws look like Phillips head, but they aren’t. A Phillips screwdriver may work but is far more likely to strip a screw. Read warning #3 – a stripped screw is a really bad thing.

You’ll really prefer a magnetized screwdriver so pick up a magnetizer when you go shopping for tools at Amazon or wherever.

You’ll also need a rocket blower or electric blower that does NOT use canned air with propellant. Getting propellant in the lens is way worse than dust. (Yes, I know That Guy used can air and his lens is fine. You might get away with it 20 times before you ruin a lens.) Plus, warning #3 will apply if you try to send the lens in for service with propellant coating the lens elements.

Finally, you’ll need a well lit workplace with room to keep screws and parts organized. My ‘well lit’ may be different than yours but I use three 100 watt halogen desk lamps on flexible arms.

Today’s Lenses:

Below are the lenses we’ll show how to dust out today, with lenses that are similar listed in parenthesis. Just click the lens to go straight to that section of the article.

1. Nikon 24-70 f/2.8 AF-S (Many Nikon “D” primes)
2. Canon 17-55 f/2.8 IS(Canon 24-105, 24-70 f/4 IS, 24-70 f/2.8 II)
3. Canon 85mm f/1.2 L
4. Canon 85mm f/1.8 (Canon 100m f/2)
5. Canon 70-200 f/2.8 NON IS (Canon 70-200 f/2.8 IS I and II)
6. Canon 100-400 IS L (Canon 28-300 IS L)

Here We Go

I’m giving examples of very easy to moderately easy places you can get dust out of in certain lenses. PLEASE DON’T EMAIL ME ABOUT HOW TO DUST A LENS NOT SHOWN HERE. Most lenses have front or rear centering elements that if removed, require factory recentering and recalibration.  You can’t do that at home. 

Nikon 24-70mm f/2.8 AF-S Rear Dust

Also applies to: many Nikon “D” prime lenses.

Difficulty: This is the easiest lens dusting of all.

As a rule, Nikon lenses are more difficult to get into, but the 24-70mm is an exception. It’s probably the easiest lens to remove rear dust from because the rear glass is a separate, fixed element that can be removed with just 3 screws.

Three small screws attach it to the side of the lens mount. Do NOT remove the small screws holding the electrical contacts in place.

Once the screws are removed you can remove the rear element – lift it out or simply turn the lens upside down and let it fall into your palm.

Blow the dust out and you’re done. Notice the spring for the aperture lever at 2 o’clock inside the lens – don’t mess with it.

When you put the element back in place, be sure to line up the slot for the aperture lever (red arrow below). Bending the lever is probably the only risk with this one. Don’t forget to replace the screws. I did that once (that’s why I don’t take phone calls during the workday – I forget where I am in a disassembly).

Canon 17-55 f/2.8 IS EF-S Front Dust

Also applies to: Canon 24-105 f/4 IS, 24-70 f/4 IS, 24-70 f/2.8 II (although these have more screws holding the front element in)

Difficulty: Very easy

Most of you interested have probably seen this from a post I did a couple of years ago, but we’ll try to be a bit clearer with this one. It’s nearly as easy as the Nikon 24-70.

Start by using some sharp forceps or a small screwdriver to peel up the makeup ring. It’s stuck on with sticky adhesive and will stick right back on if you don’t set it sticky-side down on the counter.

With the makeup ring removed you’ll see the three screws that hold the front element in place. At each screw location there are three possible holes for it to go in. You’ll want to remember which set of holes the screws go in (left, right, center) on your lens. The location of the front element will be apparent from the marks the screw head has made.

Here’s a front view with one screw removed. You can see the three possible holes (you might not in your lens, depending on the placement of the front element one or two may be outside of the slot). It’s important that the lens go back in exactly the position it was in before. In this lens the left (most clockwise) hole is used and you can see the mark the removed screw left in the front element. If you can’t see it clearly, or you’re OCD like Aaron, make a small scratch.

Once the screws are removed the front element comes out. If you don’t have a fancy suction bulb just drop it out into your palm. It’s fairly large.

The front element chamber is pretty large, but you’ll be amazed at how that huge dust speck is really quite tiny without the front element to magnify it. BTW – the three screws at the bottom of the chamber hold the front barrel in place. As long as you’re here you might make sure they’re tight. The odd shape at 11 o’clock is where this group attaches to the focusing ring key.

If you don’t have a suction bulb thingie, the simplest way to replace the front element after the dust is gone is to hold it upside down and put the lens down over it. After turning it upright you can rotate the front element to proper position before replacing the screws.

Canon 85mm f/1.2 Rear

Difficulty: Easy

It’s very easy to get rear dust out of the Canon f/1.2 prime lenses (the front is another matter entirely).

The 4 lens mount screws are removed. They are often glued in so be careful about stripping these — if the screw doesn’t come out fairly easily then quit.

Once the screws are remove you can tilt up the rear element on the side away from the electrical contacts and blow the dust out. Important: just tilt it. If you tear the contacts you will be in for a major repair cost.

Canon 85mm f/1.8 front and rear

Also applies to: Canon 100 f/2.0; Canon 50mm f/1.4

Difficulty: moderate

When these lenses get dust it tends to be on either side of the central group, so you generally need to do both the front and rear. This one is more time consuming and a bit more difficult than the previous ones, but still fairly straightforward.

Rear

Start by removing the two small screws that hold the electronic contacts to the rear mount.

Then the 4 larger screws that hold the rear mount to the lens.

Once those are removed, lift the mount up just a bit on the side opposite the contacts, put a finger under the mount and while holding the mount firmly in your other hand use the finger to pop out the plastic rear baffle.

With the plastic baffle out, just slide the contact assembly away from the metal ring a bit (there a small post in the back that inserts into a hole in the metal ring) and remove the ring.

Now you can see the PCB and the rear element is exposed. The rear group has some notches around the plastic rim — you can see one lined up above the ’85′ on the lens barrel. Remember where it lines up (or make a tiny mark lined up with some landmark). You’ll need that later.  Note the flexes and soldered wire attaching to the PCB. Your goal from this point forward is not to pull them.

The rear element unscrews counter-clockwise several turns (you wanted to line up those landmarks so you know you have it fully tightened during reassembly). If you have a flat spanner wrench you can use that to unscrew the lens.  But then again, if you have your own spanner wrench you probably don’t need me to show you how to do this.

Often you can unscrew the rear element by using your thumbnails in a couple of the slots in the rear element. One of those rubber ‘jar opener’ sheets works really well, too. Just remember – DO NOT PULL ON THE FLEXES OR WIRES while you do this. If you tear them, the lens is basically junk.

Once the rear element is unscrewed, lift it out, blow out the inside group and clean the rear group.

Reassembly is the reverse, of course. When you put the lens group back in, make sure it’s level and screws in with little resistance. If you cross-thread it the lens will be badly decentered. Tighten until you reach the mark you were at originally.

When you put the rear mount back on, I find it best to put the screws holding the electrical contacts in first (use the post in the contacts to line it up properly, then put in the screws) then put the mount screws into the lens. Finally pop the plastic light baffle back in.

Front

There are 3 screws that hold the front barrel cover onto the lens. Before you remove them make a mental note of which way the cover lines up (the distance window is a good landmark) so you put it back on correctly. It will still work fine if you put it on wrong, but someone (likely a future buyer or repair shop) will notice you’ve put it back wrong.

Once the three screws are removed the front barrel slides right off.

Inside the front barrel is some dust-catching sticky felt. Might as well clean that off while you’re here.

The front element is held on by 3 screws. As usual, you’ll find reassembly easier if you mark how the lens element should line up when reassembled.

Under 1, 2 or all 3 or the lens screws you will notice small adjusting screws that the factory used to set the tilt of the front group to zero. Don’t touch them.

Once you’ve removed the three screws holding the front group in place it lifts right off. Blow dust out from inside and under the back glass of the front group and put everything back together.

This one is a little more time consuming than the previous ones, but still pretty straightforward.

Canon 70-200 f/2.8 Non IS front

Also applies to: Canon 70-200 f/2.8 IS and IS II (with some modifications)

Difficulty: Easy, but you won’t get out all of the dust.

In general, getting dust out of a 70-200 f/2.8 lens is difficult, but most of the dust right under the front element can be removed fairly easily. Getting it all out, or getting out deeper dust, requires removing elements that require recalibration.

Really all we need to do is remove the filter ring barrel. To access it first either fold down (or remove) the focusing rubber. This exposes three holes in the focusing ring. Rotate the ring until the holes line up with the three screws (as shown below) that hold the filter ring barrel on. The IS II version has 5 screws rather than 3.

Remove the screws and the filter ring slides off. As always, you’ll want to remember how it aligns when you replace it (the red ultrasonic lines up along the distance scale window).

There is a layer of dust-protection / weather sealing tape around the inner barrel. Find the end and take it off.

This allows you to access several openings in the inner barrel through which you can blow air to get dust out of the first chamber. Again, you won’t get every speck of dust out, but you can get most of it.

Canon 100-400 IS L front

Also applies to: Canon 28-300 IS L

Difficulty: Moderate

Let’s get this out first: You may or may not be able to get into this lens with simple tools. The screws are quite tight, glued in, and rather easy to strip. So try it, but if you find you are having trouble with the screws, quit before you strip them. You’ll need to apply a lot of downward force as you loosen them. If it wasn’t for the screws, this would be an easy one to do.

First a shot to show how various barrels line up when you reassemble.

The first step is to remove the silver name ring. There are three very small slotted screws holding this in place.

You’ll need a very small electronic flat head screwdriver (1.5mm or less) to remove these screws.

Once they are out you slide the silver name ring and the red “L” ring over the end of the lens. Under the name ring are three thick screws that hold on the filter barrel.

These are the screws most likely to strip. A very good screwdriver and a lot of downward pressure are the keys to removing them. If you want to be aggressive you can put a drop of alcohol on top of the screw and let it soak in to soften any glue, or touch the screw with a soldering iron tip to heat it a bit. I’d really advise, if they don’t come out easily, to just put the name ring back on and not worry about the dust unless it’s horrible.

Once these three screws are removed, the filter barrel also slides off of the end of the lens.

Underneath this is the focusing barrel – a single tube attached to the focus and smooth-tighten rings. It is held on by a single screw with a small brass color attaching it to the thin inner focusing ring. When you remove this hold things close to your worktable. These two parts fall on the floor and you probably won’t find them again.

With the screw removed you can slide the focusing barrel right off, too.

Once the outer barrels are off, you can pull on the front of the lens (not the plastic cosmetic ring on the very front, the sides, which are black metal) and extend the lens. This exposes all of the helicoid slots of the inner barrel. You can use your rocket blower at various locations and get most of the dust out of the front of the lens. (Just in case you are tempted, the element inside at the bottom of the front barrel is the IS unit. Don’t touch it. Don’t blow on it too hard.)

Let the barrel slide back into the sleeve of the lens, put things back in reverse order, and you’re all done. I will say reassembly is usually much easier than disassembly with this lens.

Conclusion

If you’re handy and have an appropriate lens, hopefully this will help you out. I can’t emphasize enough that dust really doesn’t impact images unless it’s really bad and you shoot stopped down. But for whatever reasons, everybody wants their lenses clean. This should help you accomplish that with at least a few of them. For a while. It will be back.

I want to emphasize again, these are the easy ones. Cleaning middle elements in any lens, and cleaning any elements at all in a lot of lenses, is complicated, time consuming, and has a lot of risks.

Roger Cicala and Aaron Cosz

Lensrentals.com

May, 2013

All images copyright Roger Cicala, 2013 except a couple that are copyright Aaron Closz.

All hands in images furnished by Aaron Closz, 2013 except a couple furnished by Roger Cicala.

Images may be reproduced IF you include credit and the article includes a link to this post.

Obvious disclaimer applies – doing this voids every kind of warranty, is probably a bad idea, and we don’t recommend doing it.

But if you want to, and are handy, taking off the hood / distal barrel piece isn’t hard and does not affect lens alignment or centering. So here we go.

The most difficult part, and the only part requiring some special equipment is removing the front cosmetic ring. It’s metal and screws off, but is also glued in place. Some Isopropyl alcohol or a thin glue remover needs to be applied around the edge of the ring. A drop or two is enough. We use a syringe but a dropper would work fine. Let it soak in for 10 minutes.

Next you’ll need a soft rubber friction tool to unscrew the front ring. We cut the center out of a $5 rubber stopper, but there are a lot of options, including some premade hollow rubber rings.

Use it to unscrew the makeup ring counterclockwise a half-dozen turns or so. This was the hard part, the rest is easy.

With the ring removed you can see the 3 screws that hold the hood / distal barrel on. They are the ones OUTSIDE of the silver ring. The ones inside the silver ring are for the front element. Don’t mess with them unless you want to recenter the lens (you don’t want to recenter the lens, I promise).

A closeup just to emphasize which 3 screws you remove.

Once the 3 screws are out the hood comes off and you can go mutilate the petals to your heart’s content.

Roger Cicala and Aaron Closz

Lensrentals.com

January, 2013

Aaron made a great demonstration of this yesterday with a dropped Nikon 70-200mm f/2.8 AF-S VR II while I was off playing with autofocus.

The 70-200mm had been dropped, but it appeared to have no damage. When the incoming  technicians tested it though, this is what the optical chart looked like:

You can tell that’s bad even at 10%, but here’s a 100% crop of the centers and a corner.

Aaron took the lens apart to see what was up. When he removed the second lens group, which is encased in a single metal barrel, he found that the last element in the group (Element 9 from the front for those of you keeping score at home on your Lens Block Diagram) had gotten jarred out of place and was slightly tilted.

Just the second group is shown in the picture below. It’s sitting in a rubber stopper to keep the glass from touching anything.

Looking at it directly from the side, you can see the element is only tilted about 1.5 degrees. That’s a pretty amazing devastation on the image quality caused by such a little bit of tilt.

So, of course, Aaron glued the element back in its proper position.

The proof is in the pudding, as they say. (I’ve always wondered why they say that. I’ve never understood what that means. But I’m hungry and I like pudding a lot, so I thought I’d use that. Chocolate pudding. Maybe with some whipped cream. Yes, I’m on another diet.)

Anyway, here are the images of the test chart shot after Aaron put everything back in place. Looks like a 70-200 VR II should now!!

Isn’t it amazing how such a small tilt in an internal element has such a devastating effect on the lens?

Aaron Closz and Roger Cicala

Lenrentals.com

August 2012

Aaron is a Chicago-based photographer and retoucher who combines elements of reality and fantasy to create his images. Aaron has taught Photoshop and photography to over 100,000 people, and his images have been viewed over 15 million times on Flickr alone.

He is also the founder and president of Phlearn.com, which offers daily videos, advanced tutorials, featured photographers and more. Aaron is one creative, hard-working guy, and we’re thankful he has the time to show you guys some of the magic behind his work!

The Canon 16-35mm f/2.8L II is what I call a “superlative lens.” It is very different from anything you can get from a point-and-shoot or an iPhone. It is at an extreme, and the images that it produces reflect that extreme, bringing the viewer into another world.

“Superlative” lenses really have to stretch the extremes, so not many lenses fit in this category. The Canon 85mm f/1.2L II is a superlative in that it allows you to photograph with an extremely shallow depth of field. Anything longer than 200mm at f/2.8 I would also consider superlative, as it compresses an image far more than the human eye does. Using one of these superlative lenses will make your photography stand out.

Include More

Using the 16-35 on a full-frame body like the Canon EOS 5D Mark III will allow you to get extremely close to your subject while also capturing the entire environment. If you are shooting in an amazing environment this is a plus. If your location leaves a lot to be desired, you may choose to shoot at a longer focal length in order to crop some of it out. Sometimes your environment may not be great on its own but can be enhanced with lighting. In this example you can see how the original photo includes too much.

The back door is in view, and light is spilling into the scene from many directions. Instead of trying to change the environment physically, you can alter its appearance with light. Also a slight change of camera angle will avoid distracting elements like the back door.

In the final shot, I used a large softbox, camera left, to light the scene. A fast shutter speed allowed the light from the outdoors to go to black. Doing this made the water and the subject the focal point of the image.

Adding Drama

The wide angle lens shows off the environment and pulls you into the image. It is as though the water really is rushing towards you. Just in case you are curious, minimal Photoshop was done to the final image—we really did pour hundreds of gallons of water down these steps.

Floor to Ceiling

Using a wide angle lens will allow you to capture the floor and the ceiling of a small room at the same time. If you use this to your advantage, you can include a lot of great detail. One thing I have learned from shooting wide is that most ceilings are bare and boring.   In order to avoid the lack of detail present in the ceiling, I added a flurry of leaves to the room. Two leaf blowers were used just outside of the room, stirring up a tornado and allowing leaves to go everywhere.

These shots were composited together with the final images of the model to create a dramatic photo with detail from floor to ceiling.

Converging Lines

Straight lines made by walls and ceilings will converge more dramatically when photographed with a wide angle lens. If you can, place your subject where these lines come together, and they will help to lead the viewer’s eyes straight to the subject.

Lighting

One problem many photographers face when shooting wide is getting too much in their scene. If you are using lighting such as a softbox or beauty dish, it may be very hard to keep this equipment out of the image. At the same time, not using lights may cause your image to be underexposed in key areas.   If you expose for the outdoors, the subject of this image would be dramatically underexposed. In order to expose both, a softbox was necessary.

The subject and the background are now exposed well for the final image, but the softbox is visible to the viewer. This is where Photoshop comes in. If you do have to include lighting in the shot, be sure to take a photo in the same place with the lighting moved. Then you can simply replace that part of the image. As you can see, the final shot does not contain any of those elements, allowing the viewer to focus on the subject.

Center Your Subject

If you are shooting a person, be sure to keep them near the center of your frame when shooting with a wide angle lens. These lenses cause a bit of perspective distortion, and if your subject’s face is near the edges, it will come out looking like you printed their face on a fruit rollup and then pulled it apart.

—–

Thanks again, Aaron!

To learn more about photography, lighting, and how to Photoshop together images like these, check out Phlearn.com. They make five free videos a week and offer the most in-depth Photoshop tutorials on the internet. Pretty sweet deal if you ask us!

 Hope you enjoyed!

Caroline Bishop

Lensrentals.com

June, 2012

You see, children, once upon a time, maps came on a sheet of paper bigger than the windshield of your car but folded neatly into a little square the size of a Kindle. Maps couldn’t even say things like “Turn right in 200 yards”; you had to actually look at it and figure out where you wanted to go. But if you opened it up to look at it while driving, the map would cover the windshield and you’d have a wreck. On the other hand, if you weren’t driving, you rarely needed a map.

This presented quite a dilemma. Amateur travelers would steer the car with a knee while wadding the huge sheet of paper so they could see the area they were interested in. (This is what we did before we had texting-while-driving to distract us.) Real professional travelers had the skills of a one-armed Origami artist and could fold the map so the small part they were interested in was on top, while never taking their left hand off of the steering wheel. This was back when men were iron and ships were wood, though. Such skills do not exist today – except in certain little tripods that can be folded up to be about a foot long. But, I digress. A lot.

What was I talking about? Oh, yeah. Anyway, over time our nice, shiny, smoothly moving tripods tend to get jacked up a bit. Sand or salt-water gets in the legs and they don’t move smoothly anymore. Lever-lock latches don’t hold the legs quite as firmly as they used to and we find our carefully positioned tripod slllloooooowwwwly sliding to one side if we put a bit too much weight on it. Sometimes the internal locks and shims on the legs get knocked around and we have one leg that won’t slide all the way back into our tripod, or one section falls out entirely.

Luckily, tripods are probably the easiest things in a photographer’s kit to disassemble, clean internally, troubleshoot, and fix. So I thought I’d put together a little how-to-fix-it-up guide for those of you who have a gritty, sticky, loose, or just plain dirty tripod. We’ll start at the bottom and work our way up.

Changing Feet

Almost everyone knows it, but just in case you don’t, the feet on most tripods simply unscrew and can be replaced. Most manufacturers sell, or include, alternative feet so that you can use spikes in dirt or grass and rubber feet on concrete or rocks. But you can also simply buy some replacement feet when yours get worn out.

Cleaning and Repairing Twist Lock Legs

Most Giottos, Fiesol, Induro, Gitzo, and many other tripods use twist-lock legs. The designs differ very little and they generally function the same way. When a section of leg becomes stiff, gritty, or jams simply unscrew the lock all the way until it comes off of its threads and slides down onto the section of leg below it. There is usually some thick lubricant on the threads, as you can see in the picture below. Leave that alone if you can, but if there is a lot of sand or grit in it you may need to wipe it off and replace it when you reassemble.

As  you slide the leg section out, there will be a plastic lock bushing (in the center of the image above) that will come out along with the leg. As you pull the leg section further, you’ll feel a bit of resistance just as it’s about to come loose and will notice two half-circle nylon shims or bushings at the top of the leg (in the image below one is still on the leg, the other sitting on the desk).

Your tripod may vary a bit in shim appearance (they might be black, or a single shim that nearly goes around the entire leg, etc.) but the basic design is always the same. If your tripod leg was jammed and you don’t see shims come out with it, they probably came off and are inside the leg section above this. You may need to remove that section to find them because they’re often jammed up near the top of it.

At this point we can wipe all of the grit off of the shims and leg and clean them up nicely. You might also put a soft rag up into the leg section above to wipe any remaining grit left in it. You can probably just barely make out some dirt and grit on the upper part of the carbon fiber leg and the white nylon shims in the image above. That was what caused the leg to be gritty when sliding it in and out.

Before reassembling it’s a good idea to put just a little bit of dry lubricant, like powdered graphite, on the nylon shims and / or on the inside of the upper leg section. If you need to replace the lubricant on the threads, check your manufacturer’s website to see if they recommend a certain lubricant. If they don’t, we’ve found a waterproof, silicone-based lubricant like Novagard or Versilube seems to work fine. You can get any of the lubricants at Amazon, and, now that I think of it, it’s probably a good idea to get them before you disassemble the tripod. As with most lubricants, a little bit is enough; rub a bit of graphite on the shim with a fingertip, dab a bit of lubricant on the thread with a toothpick.

 respeReassembly is pretty straightforward. There is usually a hole in the side of the tripod leg that fits a plug in the nylon shim as shown below.

Hold the shims in place on the leg and insert. NOTE: with some tripods there is a guide in the upper leg that slides between the two shims as you insert (you can look or feel in the upper leg with your finger to see if there is). If that’s the case, line the space between the shims up properly or the leg won’t slide in easily.

After you slide the leg section a few inches into the section above, then slide the plastic lock bushing along the lower leg until it’s seated inside the upper leg (it’s halfway there in the picture below). Finally, you slide the twist-lock up, screw it back in place, and test that it locks the leg properly and the leg slides smoothly when it’s loosened. I say test it just because it sounds like a good idea. We’ve done this hundreds of times and never had one that wasn’t working just fine after reassembly.

Of course, you’ll have to repeat this for as many sections of the leg as have problems and on as many legs as have problems. I suggest, at least at first, you do one section at a time starting at the bottom section. The shims and bushings are specific sizes for each leg section and getting them confused means a lot of trial and error during reassembly.

 Cleaning and Repairing Lever Lock Legs

A lot of Benro, Cullman, Manfrotto, and Oben tripods use lever lock legs. Most use two different fasteners for each section: one that holds the section on the leg, the other that adjusts tension of the lever lock. Depending on brand you may need a nut driver, hex key, or both (like the one in the picture below) to disassemble these. Some smaller Bogen and Manfrotto tripods use a different type of lever lock that has a center pin that must be driven out with a hammer and awl. If you want to remove the lever lock on this type of  tripod, they have a video of how to do it here: www.bogentripodparts.com/repairs.htm

By far the most common thing you’ll want to do with your lever-lock tripod is adjust the lock tension. It may be stiffer than you like early on, or may get too loose and not grip the legs tightly over time. It’s simple to do: simply put the right tool (hex key or nut driver) on the bolt with the lever in open position, and slowly tighten it while flipping the lever open and closed until it has just the tension you want.

It seems a little less common for lever-lock tripod legs to get grit and sand inside, but they can. Disassembly is pretty similar to that for twist-lock legs, except for needing tools to remove the lever locks. Remove both of the clamping screws / nuts. There is a spring in the lever-lock side of the assembly but for the vast majority of tripods it will not come out when you remove the lever and nut (even if it does, it’s easy to put back).

You may need to twist or rock the locking assembly just a bit and then slide it down over the lower leg. In the picture below you can see some salt residue had gotten under the lock from the tripod being used in or near salt water.

There will be two semicircular shims (or a single nearly circular shim) as shown below, but no lock bushing when you remove the lower leg section.

You can clean things off now, just as you did for the twist-lock leg. You won’t need any silicone grease since there is no twist lock, but a bit of powdered graphite rubbed inside the upper tube or over the outside of the shims before reinserting the lower section helps keeping things sliding smoothly.

Next it’s a simple matter to replace the lever locks and bolts where they came from. One “learn from my mistakes” hint: make sure you line the lever up with the ones above it so the latches are all in a nice straight line when the tripod is collapsed. Otherwise you get to loosen and tighten them again.

Removing the Legs

It’s actually pretty rare to have to remove the legs or work at the center of the tripod where the legs come together.  Every tripod is a bit different in this area, but simply looking around a bit makes it pretty apparent how the legs can be removed. In smaller tripods, like the one below, it’s often as simple as a couple of hex keys or bolts holding each leg in place.

With larger tripods it’s often more complex, though. One common arrangement is a clam shell of two plates that can be taken apart. . .

 . . . . to give access to the leg mounts.

If there’s a center post tension knob like the tripod above, there will be a spring inside, but as long as you don’t drop it reassembly is pretty straightforward. Probably because there’s a lot less movement up at the leg mounts, there seems to be little that ever goes wrong here and it’s rarely necessary to remove them except to replace a broken leg.

Center Posts

Center posts are rather simple things and rarely require any maintenance: if sand or dirt gets on them, you wipe it off, run the post up and down a couple of times, and wipe it off again. Very occasionally something will get into the friction lock of the center post. While removing them is usually straightforward, almost every single one is different. If you look around, though, you’ll almost always see a way to remove the base plate (usually a set screw or hex screw is removed, then the plate either pulls off or unscrews). Once the end plate is off  you can remove the center post.

Other times, there is an obvious twist-lock around the center post that will unscrew just like on a twist-lock leg. Generally there is just a one-piece shim in this kind of arrangement.

Replacement Parts

There is a great deal of variation between the different brands regarding ordering replacement parts. Bogen-Manfrotto not only sell parts directly and easily from BogenTripodParts.com, they offer photos of the various parts for each tripod so you can easily get the part number you need. If you’re a do-it-yourselfer, that website alone may steer you to a Bogen or Manfrotto tripod. Gitzo also has a really great parts supply website at www.gitzo.com/service/service+repair/. You just type in your product number and it takes you to a schematic that provides all of the part numbers, which you can order online.

I haven’t found simple online parts ordering for any of the other brands. In many cases, though, if you email customer support at the manufacturer of your tripod, they will try to get a part for you. It’s often helpful to have a picture of the part you can send them. You can occasionally find parts on eBay. You may also find broken tripods for sale there at very low cost.  Here’s a hint: if you buy a tripod with one bad leg you can use one good leg to fix your tripod, and sell the other good leg for almost what you paid for the broken tripod. Or keep it, just in case.

Roger Cicala and Aaron Closz

Lensrentals.com

June, 2012

All photos courtesy Aaron Closz. All fingers in photos courtesy Roger Cicala

Strictly speaking, decentering would involve one or more of the lens elements being off of the central axis of the lens. This would prevent the curved surfaces of the lens from bending the light properly. In severe cases it could result in halos or ghosting. In most cases it causes softness, especially away from the center of the lens. A decentered lens may be normally sharp in the center, but very soft in the corners. Or it may just be soft and blurry everywhere. Most lenses have one or more elements that are adjusted to correct centering. Which element that is varies depending on the lens type and design. The front element is often a centering element, with the rear element being the second most common centering element.

Diagram of a Perfect Lens

Lens with the Front Element Decentered

An element can also be tilted to one side or another. Strictly speaking this is not decentering, but it can have similar effects, so people often say a lens is decentered when in fact it’s tilted. In this case one axis may remain sharp, but the other will be out of sorts. If the tilt is side-to-side, the top and bottom of the image might be fine, but both sides soft. If it is corner-to-corner the top right and lower left corners might be fine, while the top left and lower right are soft. High quality lenses usually have one or more elements on which the tilt can be adjusted by two or three elliptical collars.

Lens with the Front Element Tilted

The third problem that can occur with lens elements is spacing. If elements aren’t the proper distance apart the lens may not focus the image sharply, or might not focus all the way to infinity. But the lens is not decentered and the tests we’re describing would be normal. There are usually a couple of elements that have ‘critical spacing’ within the lens. Theses are adjusted when the lens is assembled either by removable shims or by installing an element on a ‘ramp’ so that rotating the element moves it forward or backward.

Lens with a Poor Spacing of a Central Element

Some Generalizations

It would be nice if we could say “a decentered lens looks like this” and “a tilted lens causes that”. Unfortunately lenses are too complex for that. But one common issue people ask me about is a lens that seems OK in the center but is very soft in the corners. Sometimes that’s just how the lens is designed. But if the lens doesn’t have a reputation for soft corners, it may well be that the copy in question is decentered.

The Way It Used to Be

Back in the days of film and manual focus lenses, most repair shops had a centering collimator. It shined a star chart or a chart of concentric circles through the lens. If an element was decentered the chart would flare or be distorted in one direction. The technician would then adjust those elements that could be adjusted until the lens was properly centered. Obviously in film days you didn’t take a test shot, send it off to be developed, make an adjustment, take another shot . . . . it was all done off camera.

When lenses became more automated, so did testing: Lenses are mounted to the manufacturer’s electronic test system and most of the adjustments made electronically – or the computer report suggests which lens elements need be adjusted. The equipment is breathtakingly expensive and only the factory and some (not all) factory authorized centers have access to it. Standard centering collimators became a thing of the past, except for some specialty shops. (You can find them on eBay every so often if you want one to keep around the house.)

A Simple Test for Decentering

If you want to correct a decentered lens you need an optical bench, a computerized MTF program, or at the very least a lens projector and a lot of knowledge about which elements can be adjusted to correct an abnormality. But if you just want to check and see if your lens is centered properly (at least for most lenses) you don’t need much equipment at all. Now that we have live-view focusing and the ability to look at images in real-time, we nearly have the same thing as a centering collimator built into our camera and lens. You need just a couple of accessories: a tripod to give your camera a stable platform and a simple chart.

The screening test I’m going to describe is not perfect: a few lenses (particularly ultra-wide and 10x zooms) will give false-positive results; and this test won’t detect other causes of softness like problems with spacing of elements. But it’s at least 95% accurate for detecting decentering in our experience (which is for several thousand lenses tested over-and-over).

We use a the Zeiss modified Siemens Star Chart. Star Charts are often used as focusing aids, which is one of the reasons we put them on the resolution charts we use for Imatest and our other testing setups. You determine the lens is properly focused as the rays of the stars get closer and closer to the center. The Zeiss version adds a small white circle around a small black dot in the middle of the star chart. You can buy them for about $30.

Zeiss Siemens Star Chart

If you manually defocus the lens just a bit, the star rays and the white and black circles in the center blur, of course. If the lens is in proper alignment and pointed directly (lineup isn’t critical, you can eyeball it) at the star, the white and black circles remain circular as they blur. But if the lens is decentered or significantly tilted the center blur will ‘flare’ out in one direction or another as you defocus.

For example here are star charts shot just out of focus using four Canon 24-70mm f/2.8 L lenses at 70mm.

Even at the low resolution of blog-post graphics you should be able to tell that one of these things is not like the other: the lens in the lower left has a blur which is flared out toward 9 o’clock while the other three lenses have nice round blurs. The nice thing about this test is it’s not very set-up critical. The chart doesn’t have to be exactly in the center of the lens, you don’t have to line the lens up at exactly right angles to the chart, it doesn’t even matter which way you go out of focus (near or far) or exactly how far you go.

Let’s look at the resolution tests we did on the same 4 lenses using our Imatest lab – keeping the graphs in the same positions as the star patterns were above. Yellow areas are the highest resolution, blue are worst.

Imatest results for the 4 lenses

You probably notice that our lower left lens (the one with the flared star chart) has a pattern much softer on the right side. Also note the vertical axis (which shows the peak resolution) is different for this lens (the program automates the axis). The other three lenses peak near 800 line pairs, while the lower left lens peaks at about 600. It’s significantly worse than the other lenses.

Our star-chart flare did a nice job of identifying this decentered lens. The other thing that’s nice is the expensive Imatest lab shows me exactly how much the lens is affected, but it doesn’t show WHY it’s affected. The star chart made it pretty obvious the lens had a centering problem. We recentered the front element (the most common place for decentering on this particular lens) and the lens returned to perfect resolution.

If you don’t have $30 to spend on a Zeiss Star Chart, you can make a reasonable substitute yourself: just stick some white rings (like notebook paper reinforcing rings) on some black posterboard.

The flare isn’t as easy to spot as with the star chart, but it’s still noticeable. Here are the same four lenses that were used for the example above. Look particularly at the black center and see how it bleeds out onto the white circle at 5 o,clock — the opposite direction from the white flare noticed above. There is still some white flare noticeable: compare the outside of the white circle at the lower right and upper left areas. It’s not as easy to spot as the Star Chart flare, but it’s there (and this chart is free).

Uses and Limitations

Using the Star Chart as a poor-man’s centering collimator is a nice screening tool. It’s not perfect by any means. Some consumer grade zooms (particularly superzooms), some retrofocus lenses, and a few others show a pattern like this even when they are perfectly aligned, but those are the exception. For the majority of lenses, seeing a decentering pattern when the lens seems soft provides you some confirmation that the lens has a problem and may need a trip back to the factory. It can often answer the ‘is it me, or is it the lens?’ question. It may provide some further data when you’re trying to decide if the corners on your new lens are supposed to be sharper than they seem.

Because I know some people are going to ask, I don’t recommend trying to adjust lens elements at home using this method. Centering the lens element to remove the flare can be a good starting place and we do it here. But it’s just a starting place and you need a LOT of other equipment to fine tune the resolution (especially in a zoom). There are some lenses that don’t have any elements that allow tilt or centering — a factory rebuild is the only option when it gets out of sorts. With others, nearly complete disassembly is required to make such adjustments. And, of course, opening up your lens voids any warranty.

Changing that old LCD cover for a new one is easy to do and inexpensive. We’re going to show you how using a 5D Mk II for an example, but changing it out on other cameras is exactly the same (as is changing out smaller secondary LCD covers if your camera has those). For almost all Canon and Nikon cameras you can find factory replacement covers (and tape, make sure it comes with tape) on eBay or from some camera repair shops that resell parts. You can also buy them direct from Canon or Nikon parts at the moment, but Nikon plans to stop selling all parts soon except to authorized repair centers (who won’t resell parts) so Nikon supplies will probably be drying up. You can sometimes find LCD covers for other brands, but they’re more difficult to come by.

Once you have the new cover, changing won’t take more than 15 minutes. And I should note, all we’re doing is changing the cover, we aren’t doing anything to the actual LCD itself. BUT, if you’re clumsy you could scratch the actual LCD while doing this and that will require an expensive repair. So consider yourself warned.

Tools and Parts

First, you need a camera with a nasty LCD cover like this one:

Plus a shiny new replacement LCD cover and the tape needed to apply it (about $20-$35 on eBay depending on the camera)

As for tools all you need is a hair dryer and something flat and thin to pry up the old screen: X-acto knife, very small flat screwdriver, etc.

Taking the old cover off

Use the hairdryer on medium heat to slowly warm up the LCD cover on the camera. You need to get it warm to the touch to soften the adhesive, but you don’t want to cook the camera’s electronics. How warm? Well, like I said warm (not hot) to the touch. I’m not OCD enough to take the temperature of the screen, but it usually takes 2-3 minutes on medium heat.

Once it is warm, find the corner of the LCD cover that seems to have the most room to insert a small knife, screwdriver, etc. Personally, I use a lens cloth under the tools to protect the camera’s finish and find that two pry tools work better than one. The cover is only a mm or so thick and you DON’t want to let the tool move over the LCD screen if it slips. Notice in the picture that both tools are aimed away from the LCD.

Different people recommend different ways to do this. One of the more common is to go ahead and break the cover which makes it easier to pull up. I haven’t been able to summon up the guts to try this method, so I stick with prying up. It may take a couple of times reheating and reprying but once a corner starts to come loose, the screen will pull up very easily.

Finally, you’ll need to clean up. There will almost always be some old tape left that you can gently scrape off with a screwdriver blade or similar tool. I do not recommend using an adhesive remover – you don’t want any gunk getting on the LCD. As for the LCD screen itself, simply blowing it off with a rocket blower should be all you need to do. But if necessary we’ve found using a Lenspen or soft brush causes no problems.

Applying the New Screen

For most cameras, the replacement tape comes on an LCD size pad with a center protective area –  the double-sided strip of tape is only around the edges. Simply remove the paper over the tape

and apply it to the LCD area.

Smooth it down firmly and then remove the paper backing, leaving only the tape behind. It always amazes me how easily this works.

Make one last check to see if any dust has settled on the LCD, then place the new cover on top of the tape, press down on the edges firmly, and you’re all done. Nice, shiny clean new LCD cover!!!

Strictly for your benefit, my readers, I have demonstrated what happens if you don’t check the underside of the new LCD cover for dust before you apply it. If you notice it (like I did) before you’ve pressed the edges down tightly you can probably pry a corner up and blow it out. If not, well, go back to step 1.

Roger Cicala

Lensrenals.com

February, 2012

But I’ve had over 100 requests now, so I’m finally going to cave in. Since I’ll be mentioning and recommending some products by name, my usual disclosure applies: we use what we use because we like the product, sometimes a lot. Unlike 99.9% of the internet we don’t get discounts, kick-backs, click-through fees, or sell any of the things recommended at a profit. I don’t put any links to the products to make sure that’s clear. You can find it all with a quick Google.

What this is:

Mostly it’s proof that the old saying “Be careful what you ask for. You might get it.” is true. This is going to be massive overkill for 98% of people who asked how we clean lenses. You certainly aren’t going to go out and buy all the supplies to do this to your own lenses every day (well, except for a few of you that have major Lens OCD: you know who you are). But there will certainly be some things you’ll want to try, and probably a few tools you don’t know about.

On a busy day we clean about 500 lenses, on slow days maybe half of that. We clean to what for most of you would be an unreasonable standard – not just the front element but the entire lens. Over the years we’ve probably tried every cleaning method there is short of kerosene and a blowtorch and we’ve considered that once or twice. That doesn’t make our way the right way. It just makes it a way that works well for us.

What we use:

I’ll start with a photo of one of our cleaning stations so you get an idea of how over-the-top our cleaining methods are. You may want to just say never mind and move along now. Or if all you want to know about is how we clean front elements, skip down toward the end of the article.

Supplies at a Lensrentals Cleaning Station

Don’t get me wrong, you don’t need half of this stuff. A lot of it is useful to us only because we do so many cleanings a day, and some of it because some of our techs prefer one thing to another. But for completeness, here’s what we have at each station, using the numbers in the picture to give you location:

1: Large yellow chamois, Zeiss individual lens cleaning cloths in box, and blue microfiber cloth.

We use the chamois for cleaning barrels and cases. We don’t usually use microfiber cloths on front elements: you never know when there might be a piece of grit in them which could scratch the elements. We use fresh Pec Pads for that. But microfiber cloths are more absorbant and we will occasionally use a new, clean one on front elements.

2: Lint removing brush (red) and two size lint rollers above it (Sensor Loupe above that doesn’t count in this article).

Used for cleaning bags and the inside of lens hoods (the ones that have a felt lining).

3: Giottos Rocket Blower. The one thing everyone should already own.

4: Cleaning solutions — Eclipse, ROR, Purosol Lens Cleaner, Purosol Sport and Marine cleaner. Two canisters of premoistened electronic cleaning wipes behind them.

Purosol cleaners and electronic wipes are used for the outside of lenses, hoods, and caps. We occasionally, but not often use Eclipse or ROR on lens elements. ROR is especially good when there are oily deposits.

5: DataVac Electric Blower. The greatest invention ever made, but you probably don’t need one.

We avoid canned air: it can have propellants or other liquids that can stain glass (and it’s relatively expensive in quantity). The DataVac Electric blower is the only thing we know of that uses no propellants or lubricants plus it’s EXTREMELY powerful. Many times greater airflow than canned air. We use the Rocket Blower for sensitive places like front elements, the DataVac is too powerful. But for about $50 it keeps us all from getting carpal tunnel syndrome from pumping the Rocket Blower all day.

6: 8 different sizes and types of Lens Pen. Notice the large rectangular LapTop LensPen just to the right of the chamois, just to the left of the “6″. More on LensPens later.

7: Two toothbrushes and in the lower right corner Pec Pads.

Soft toothbrushes are the only way to get dust and grit out of the cracks and crevices of front lens caps (Canon caps are particularly prone to gather it). A toothbrush and Purosol cleaner does a wonderful job of cleaning the grooves of rubber zoom and focus rings. We use Pec Pads instead of microfiber cloths on front elements: we know a fresh Pec Pad doesn’t have any grit on it. That’s hard to say about a previously used microfiber cloth.

Cleaning Overview

Our basic method is cleaning from outside in: Case or pouch, then outside of the lens, the caps, and finally glass. There’s no sense cleaning the lens barrel and then putting it back in a dirty case, or cleaning the front element and then putting a dust filled lens cap back on it. Cases are the easy part, of course. Simply blowing them out with an electric blower or vacuuming them takes care of dust, and a lint brush or roller handles anything left over. Canvas type cases, in particular, look much better after a good vacuuming.

The Lens Body, Hoods, and Caps

Obviously cleaning this doesn’t make the lens work a bit better, but it’s nice to have a clean lens. And it’s definitely worthwhile for a lens you plan on selling. The plastic and metal on the outside of the the lens barrel, hood, camera bodies, and caps are easily wiped clean with a chamois dampened with cleaning fluid. We generally use Purosol. It’s not the strongest cleaner but it leaves no residue and doesn’t seem to cause any adverse effects on the rubber zoom or focus rings, or plastic distance windows. Tough areas are spot cleaned with a premoistened electronic wipe or a bit of eclipse.

The inside of hard plastic hoods can be cleaned in the same manner, but lint rollers or brushes are the best way to get dust and dirt from the inside of felt-lined hoods, particularly supertelephoto hoods. The inside of clip-on front element caps get the dust blown out of course, but dust tends to hide in the nooks and crevices of many caps, and inside the spring loops of Canon caps in particular. Brushing with a dry toothbrush usually dislodges it so it can be blown away, or a toothbrush sprayed with cleaner used to get the tough dirt out.

Front Elements

This is what most of you want to know about. The key to front element cleaning is to avoid damage. Blowing is always done first. You can’t scratch an element by blowing and most large particles can be blown off using a Rocket Blower. (Canned air or a DataVac is really too strong, and as mentioned earlier it’s possible to get some residue on the element using canned air.) Brushing (we use the brushes on the LensPens) is always done second to dislodge any particles, followed by blowing again to remove any particles loosened up by the brush. If further cleaning is needed after blowing and brushing, that’s fine, but blowing and brushing is always first.

Our next step revolves around LensPens. We like several things about them: no liquid residue, simple and easy to use, gets into the edge of the lens better than most other methods. And out of the office, they’re small and easy to carry around. They come in a variety of types and sizes and we use a number of different ones. Smaller ones are perfect for camera viewfinders, angled edges are great for lenses with deep edge recesses like fisheyes, etc.

A variety of LensPens sizes and types. On the left is the Laptop Lenspen, which we find perfect for supertelephoto front elements. Notice the two on the right: when you start to see them look like this, it's time to throw them out. Actually the one that's next to the Laptop LensPen is about ready to go. When you see rubber instead of felt around the edge, the LensPen is used up.

The key to using a Lenspen is that you charge it (put the cap all the way on and take it all the way off) with each use so that the tip gets more cleaning dust. Also after using the lens pen, you should go back to blowing and brushing: if you look carefully with an angled light, you’ll see a little fine grain dust has been left after the Lenspen use.

The most important point, though, is to not overuse a Lenspen. Once the felt on the tip gets worn, the rubber underneath doesn’t clean, and can leave marks if used with too much pressure. We get, at best, 100 cleanings from a Lenspen, but that varies by which brand we’re using and how big the lenses are being cleaned.

Lenspens do a great job on routine dirt, streaks and grime, but they won’t get more stubborn “stuck on” gunk off of the front element, and aren’t great with oily residue either. A wet cleaner is required for this stuff. We use Zeiss disposable lens cloths — individual sealed pouches with a lens paper moistened with cleaner inside. We like that these are single use. Like I said, we’re more paranoid about a piece of grit on the cleaning cloth damaging the lens than anything else. They’re also convenient to toss a couple in your camera bag. But Eclipse on a PecPad works just as well, and ROR is what we reach for when we see obvious oily residue on an element.

PecPads are single use, too, and we like that, but they aren’t as absorbant as a cloth. When we’ve had to use a fair amount of wet cleaner, sometimes a microfiber cloth is used to wipe off the cleaner simply because it’s easier to get the streaks off than PecPads are. You may have noticed a microfiber cloth on the desk in my first picture: that cloth wouldn’t be used on a lens element, it would be for less critical things like LCD covers. Only a clean, been-kept-in-a-pouch microfiber cloth should touch a front element.

Many of you know we don’t get freaked out about tiny front element scratches. We test to make sure they don’t cause flare or contrast loss and otherwise don’t worry with them, they won’t do anything else. But a lot of people, including perhaps the future buyer of your used lens, will care a lot, so it’s worth trying to keep the element as pristine as you can.

Rear Elements

Cleaning rear elements is certainly more important from an image quality stand point than front elements, but since rear elements aren’t exposed to the environment it’s rarely necessary to do more than blow off dust. Many lenses are “rear focusing” so before cleaning the rear element turn the focus ring to bring the element up to the surface of the lens.

If more than blowing and brushing is required, be careful to keep your fingers away from the electrical contacts on the lens when cleaning. Just a bit of skin oil on the contacts can interfere with electrical signals transmitting between camera and lens. If you do find an ERR message after cleaning a lens, you can lightly rub a clean pencil eraser over the contacts to remove the oil. There are people online who give longwinded warnings about this eroding contact metal, and it might if you do it every day, but every factory repair service we know of uses that technique, so we do to.

Is All This Necessary?

Absolutely not. Those of you who wear glasses just take them off and look at them. They can be fairly filthy and not interfere with your vision. The front element of your lens can also be fairly filthy and not affect image quality at all. If you don’t believe me go put a a couple of 1/4 inch wide piece of post-it note on your front element and take some pictures. You won’t be able to tell it was there, any more than you can tell a fair amount of dust is there. Or look at our example or Kurt Munger’s. That being said, very wide angle lenses at small apertures may be the one exception to the rule: the depth of field in that case may come close to bringing front element dirt or scratches into the plane of focus. Maybe.

Oily films or haze or thick coatings of dust can definitely affect image quality, though, and probably should be cleaned as soon as possible. However, lots of small scratches can affect contrast and deep scratches can cause lens flare, so the key is to keep your lenses reasonably clean but avoid putting multiple cleaning scratches on the front element. So we believe blower, brush, and meticulously clean (read single use) cloths for cleaning are the key.

But that’s just our opinion. We know breathing on the lens and using the corner of your T-shirt usually works. Almost any cleaning method usually works and has it’s advocates. Just letting the lens be incredibly dirty usually works, too. But most of us (and as best I can tell all of our customers) like their gear to look as good as it did when they first got it, and these are the methods we use to do that.

A note on comments

With a bit of hesitation, I’m leaving the comments section open in this article. Thoughtful comments, questions, and suggestions are welcome. What I’ve written above is the way we’ve performed some 120,000 cleanings, but that doesn’t mean I know it’s the right way. The only thing I know for certain about cleaning lenses is that sandpaper and chisels should be used, at most, sparingly. Everything else is open for discussion.

But this isn’t a forum, it’s our clubhouse, and we don’t find the “anyone who doesn’t do it my way is an idiot” type of comment acceptable. There are already plenty of forum threads about cleaning lenses that are full of those posts, there’s no need for more. Of course, anything that hints of “selling a product”, even the ones we’ve recommended, in the comments will be deleted immediately. Our readers are big boys and girls, they know how to use Google to find what they want.

Roger Cicala

Lensrentals.com

May 2011

I don’t mean to suggest we’re lens reviewers, dissecting and measuring every possible aspect and index of a lens. That takes days, tons of equipment, and a mindset that I don’t have: full-blown obsessive-compulsive nitpicking disorder. I’m glad there are people who do that. I’ll never be one of them.

(Don’t get me started on the whole are-lens-reviews-worthwhile thing. I find it very similar to measuring the height of one third-grader and then saying “all third graders are 4 feet, 7 inches tall and weigh 52 pounds.” Someday someone will start evaluating 20 copies of a given lens, include the copy-to-copy variation in their reviews, and in a short time will own the lens review business. But that’s another topic.)

Why Bother?

When we get that shiny new box home, we expect it to be perfect. And it probably will be. But after opening some 8,000 shiny new lens boxes I can assure not all of them are. Whether its quality control at the factory or getting knocked around in shipping our experience is about 2% of new lenses need to be exchanged. It varies by brand and it varies by lens complexity (an autofocus zoom with image stabilization is more likely to have problems than a manual focus prime). But every lens needs at least a basic checkout when you first get it home. Used lenses, of course, require it even more.

There are several levels of testing and examination one can do. The simplest is go take some pictures and see if they look okay. This works well, and has the advantage of getting to take pictures, but has some shortcomings, too. First, you may not notice a problem until it is too late to return or exchange the lens. Second, if something is wrong, simple photographs don’t usually determine what kind of problem the lens has. This lens is soft is a good article title, but not a good description of a problem.

(BTW – if you send a lens in to factory repair with “This lens is soft” as the only description of the problem, chances are extremely high that it won’t be fixed. Trust me on this. We have 20 lenses a week go in to factory service. We’ve learned.)

At the other end of the spectrum is Extreme Tester Guy (and you are a guy, there are no Extreme Tester females) who will spend 16 hours testing a lens in every way possible including the laser collimator he keeps in the garage. He’ll send back 6 copies to get the perfect lens which he won’t take pictures with because a new lens has just been released and he’s too busy getting a perfect copy of that one. This article will just bore Extreme Tester Guy, he really wants to be a lens reviewer.

But without taking it to extremes, a little basic testing does several things. It will let us know the lens we bought is what we expect it to be, that its assembled properly, functions as it should, and provides a reasonable match for our camera (if you don’t understand what I mean by that last statement, you might want to read the two “This Lens is Soft” articles).

Testing will also show us some important characteristics of the lens that weren’t listed on the B&H blurb or the manufacturer’s website. The marketers are quick to tell you it has +Supermicrosecretformula coating_, 4 aspherical, and 2 ultra-beyond-low reverse distortion elements. BUT do they ever tell you if it focuses using internal, rear or front element groups? If it is parfocal (if you zoom in on the subject is the lens still in focus, or does it need to be refocused)? Is the plane of focus flat or curved? How soft are the corners wide open and at what aperture to they get sharp? Does it have barrel or pincushion distortion? These are things a bit of testing will show us about the lens. And they are good things to know that will let us use the lens more effectively.

The manufacturer goes to great lengths to show the aspherical and low dispersion elements, but don’t show you which ones zoom or focus.

Step 1: Examining the Lens

But before we start optical testing, we need to do some basic hands-on, touchy-feely examining. Some of this is to make sure the lens is in good shape, some to make sure we know how it is going to work. More new lenses fail my touch-and-feel tests than actually fail optical testing.

The Barrel

If the lens is poorly assembled now, its not going to be better after a year of use. The lens barrel is made of several different cylinders assembled together. There’s usually a joint under the rubber zoom and focusing rings and often another near the end of the lens just under the filter ring. Gently move, rock or extend each segment of the lens and ask yourself the following questions:

• Are any sections loose from the next?
• Can you rock the filter ring?
• Do all the screw holes (including the ones at the lens mount) have screws in them?
• If there’s an extending internal barrel does it slide back and forth easily when you zoom and focus?
• Does the front ring accept a filter easily (more important to check in a used lens, but we’ve seen a few new ones with defective threads).

While we’re here, gently shake the lens and make sure there’s not a loose screw rattling around inside. Yes it happens. (If the lens has an image stabilizing/vibration reducing mechanism, this may rattle a bit when you shake the barrel. Don’t freak.)

The Focusing Mechanism

This isn’t for accuracy. That comes later. Set the lens on manual focus and run the ring back and forth a few times (even if you’ll never use manual focus).

• Does it move smoothly with no catches or gritty sensation? This is also the time to note what part of the lens moves when focusing: front element, rear element, or internal group (neither the front or rear elements move when focusing).
• If it’s a zoom lens, check the focusing at both extremes of the zoom. On the Canon 70-200 f2.8 IS II lens for example, the rear element doesn’t move during focusing when the lens is at 70mm, but moves a great deal with the lens at 200mm.
• If the front element moves, does it also rotate (makes it very hard to use polarizing filters) or is it nonrotating?
• Does the distance scale rotate properly when you move the focus ring?
• Is there a clutch for manual focus, a switch, or is the manual focus ring always active?

Then switch to autofocus, mount the lens to your camera, and repeat.

• Does it autofocus smoothly?
• Does the focus motor sound like your other lenses?
• Finally, autofocus on something close and then immediately on something at infinity. Then reverse the process. How long did it take?

A slow autofocus system doesn’t matter when you’re shooting Macros or portraits, but it can make a lens useless for sports or street shooting.

(For those of you with too much time on your hands, if you want to quantify focus speed do the near-far autofocus test right next to a microphone plugged into your computer. You can open file in an audio editing program and see exactly how long the lens motor was buzzing.)

Zoom Mechanism

Of course you want to test to see if the zoom mechanism is smooth, both going out and coming back. If the lens zooms by extending the front element (or extending an internal barrel) make sure there are no sharp, sudden catches or areas of high resistance. If there is an extending barrel, make sure the internal barrel is clean with no scratches that might indicate rubbing when zooming. Also check that the barrel isn’t loose when extended, it shouldn’t rock back and forth.

If the front element doesn’t extend, look at the rear element during zooming. If the rear element is part of the zoom mechanism it will move into and out of the barrel during zooming. Why is that important? Rear element zooms tend to have shorter than advertised focal lengths when focusing on near subjects. It may be 300mm at infinity, but only 240mm when focused 9 feet away.

Glass and internals

Look at (not through) the front and rear elements for scratches, coating defects, etc. Front element flaws are of minimal importance, but anything wrong with the rear element (scratch, coating flaw) may have a great impact. Then look through the lens while moving the focus and zoom rings. A bit of internal dust, even straight from the factory, isn’t unusual and is of no consequence. Things like a loose screw, piece of cloth, scrap of metal, or a broken internal element (yes, we’ve seen all of those in brand new lenses) probably are.

Mounting Ring

Mount and dismount the lens several times on the cameras and ask yourself the following questions:

• Does it go on easily but firmly?
• When seated is it firm with no looseness?
• Does the locking pin catch properly and then release easily when you push the camera’s dismount button?

Principles of Optical Testing

There are several principles to testing that are all too often ignored, but each is true (and obvious if you think about it a bit).

1. If the fixed elements or mount of a lens are out of spec the lens will be bad at all parts of its zoom range and when focusing both near and far distances.
2. With some lens designs an element 1mm too far forward or back will cause the lens to never focus sharply.
3. An element tilted as little as 3 degrees from the plane of the lens can cause side-to-side or top-to-bottom issues sharpness differences.
4. An element just a bit off center can cause chromatic aberration, astigmatism, coma and edge softness.
   Modern lenses may have 15 or 17 elements, each of which could possibly be out of spec.
5. If the zoom elements are out of spec the lens may be excellent in one portion of its zoom range and horrid at another focal length. (But every zoom is usually slightly better at one end of its range than the other. I’m not talking about that, I’m talking about really bad in one part of the zoom range.)
6. If the focusing elements are out of spec the lens may work fine on close objects but not at infinity, or vice versa.
7. If the autofocus electronics and algorithms aren’t accurate or camera-lens communication isn’t good the lens may front or back focus.

The primary point of this is that you must test zoom lenses at least at both ends of the zoom range (and probably in the middle too), and test all lenses focusing on both close and distant targets. And a key point in testing your lens is comparing each quadrant to the other quadrants, not just “is it sharp”. In fact, center sharpness is probably the least important thing to consider when testing a lens.

Step 2: Front- and Back-Focus Testing

We start by testing autofocus accuracy because if the lens is not focusing accurately the other tests are meaningless. Even a manual focus lens should be tested for focus accuracy on an SLR – the viewfinder and sensor may not be exactly calibrated in the camera, and if the lens has “focus confirmation” electronics, that is, in our experience, more likely to be inaccurate than standard autofocus.

Set Up for Depth of Field and Focus Testing

This requires regularly marked surface set up at angles to a focusing object. We use a LensAlign Pro because it’s quick and very accurate, but its not necessary. The marked surface can be a ruler or yardstick set at angles to a focusing target for near testing and a fence (board, chain link, brick, doesn’t matter) with some obvious focusing target for the far testing.

A lot of people use computer generated moir� targets for autofocus microadjustment, and they are fine for that, but they don’t give all the information we need for lens testing so I don’t recommend them for this purpose.

Focus accuracy

Focus accuracy testing is done with a single focus point selected (center point unless you have some very odd reason to do otherwise). We begin with the lens at widest aperture and then repeat with the aperture stopped down a bit.

The process is quite simple: we autofocus the center point at the test target and then check to see where the sharpest focus actually is on the ruler or marked diagonal line. They should be very close. There are several things that need to be taken into consideration:

• Every lens can focus differently at near and far distances. Test at several distances.
• A zoom lens usually focuses slightly differently at the minimum and maximum zoom ranges (and sometimes in between too).
  
  This 24-70 f2.8 focuses perfectly at 24mm (left) but backfocuses slightly at 70mm (right).
• Some wide aperture prime lenses exhibit focus shift: they may focus accurately wide open, but then backfocus or frontfocus slightly as the lens is stopped down.
  
  A wide aperture lens with no focus shift: note that the lens is a bit backfocused wide open (f1.2) and remains that way as the aperture is decreased.
• Autofocus accuracy is an interaction between the camera (every copy of which is slightly different) and the lens (every copy of which is slightly different). Get over the fact that your camera is perfect because it is perfect with some other lens. Below are 5 focus checks done with the same Canon 85 f1.2 on 5 different 5D Mk II bodies, for example (look at the number 4s to see that no two are exactly the same).

The same 85mm f1.2 lens tested on 5 different copies of the same camera body. Notice there are slight differences in front / backfocus with each body.

The summary of all this is we first have to check the lens at widest aperture and at least at both ends of the zoom scale and several different distances from the test target.

If our camera has autofocus microadjustment we then adjust it for the best compromise, getting it perfect where we want to use the lens. If I’m going to use my 24-70 zoom usually near 70mm for portrait shots 15 to 20 feet away, I’ll zero the adjustment there. If I’ll be shooting my 300mm prime lens on distant wildlife, I’ll zero it there.

If the lens is a wide aperture (f1.8 or lower) I’ll also do some sequential shots at various apertures to check for focus shift. When a lens has focus shift, the point of focus changes slightly as the aperture is stopped down from wide open. Eventually the larger depth of field from reducing aperture overcomes the focus shift, almost always by f2.2 or f2.8. This isn’t something I can correct, but its good to know that I can shoot my Sigma 50mm f1.4 either wide open, or at f2.2 or higher, but in between because it won’t focus accurately.

One other thing to check with a wide aperture lens is spherochromatism (also called secondary longitudinal chromatic aberration or longitudinal color shift). Spherochromatism occurs in many wide aperture lenses because while the lens is corrected for for chromatic aberration in the in-focus area, the out-of-focus areas in front of and behind the plane of focus can’t be corrected and will have magenta or green tints. There’s nothing to be done about it, but its good to know how severe it is. In problem lenses you can avoid large white areas if the foreground or background when framing your shot.

Example of a wide aperture lens with significant spherochromatism. Note the purple tinge in the forground and green tinge in the background.

Once we have the lens focusing as accurately as we can, we move on to Flat Field testing. Of course there is an occasional lens that needs so much autofocus adjustment that you don’t have to test further: if you have to set your camera to +/- 15 or more, it may be better to exchange for another lens. And of course if your camera doesn’t have microadjustment you have to decide what is, or is not, acceptable.

Flat Field Testing

This is the part of testing that will give you the most information about your lens, so its important to set it up correctly. The key to flat-field testing is that everything is flat (duh) and lined up accurately. How flat and accurate depends on depth of field of the lens, which changes with the aperture and the distance from the target. If you’re testing an f/1.4 prime lens at near distance it has to be very accurate. An f/5.6 lens at far distance, not quite so much.

Flat Field Set Up

A fairly large building (windows are great for detail) makes a superb far-distance target. You can assume the building side is perfectly vertical so using a bubble level to set the camera on tripod to vertical is very straightforward.

Any wall can be used for near-distance testing. I recommend downloading and printing some USAF 1951 test charts (they can be found online, including here ) You want one in the center of your image and at least one in each corner. A few pieces of cut up newspaper will work too.

If you want to be more complex, I recommend the simple Resolving Power chart from Edmund Optics that you can buy for less than $20. It may not be worthwhile to test one lens a year, but is certainly not a bad investment for a camera club. There are lots of other test targets available online and most do the job just fine.

Edmund Optics Resolving Power Test Chart

Setting up the Near Distance Flat Field

1. Assuming your wall is vertical and straight make sure your test targets are placed smoothly and tightly on the wall. If they’re lumpy and bumpy, they aren’t accurate.
2. Place your camera on tripod so the center of the lens is level with the center of the test target. A laser pointer held along the lens barrel can be used for targeting and to confirm centering. A bubble level (built into the tripod or a more accurate hardware level) confirms the lens is lined up vertically.
   

   Camera centered on tripod for testing

3. Make sure the camera is not pointed at an angle right or left: this could make one side of the target out of focus compared to the other. The simplest and fairly accurate way is to measure an appropriate distance from the wall (say 15 feet, but whatever is appropriate for the lens focal length) from either side of the test target. Then draw a chalk line between those two points. That line should be parallel to the wall. You can line up the camera with that line using a yardstick and drop string if you want to be a bit obsessive.

But let’s be honest: most of us are going to line up the lens so its centered on the tripod, use the bubble level on our tripod and eyeball judge the rest of it. And that will work just fine 95% of the time. If your results look bad, then you can always go back and measure carefully to make sure it’s the lens with the problem, not your setup.

Flat Field Optical Testing

Most people want to jump in and see how much resolution the lens provides at its center point, but unless the lens is horribly soft that isn’t going to tell us much. Photographing a centered resolution chart gives you almost no information about the lens.

• Center resolution is pretty good and fairly comparable on most lenses. A more expensive lens usually gets you more aperture or better resolution away from center.
• A wide angle lens won’t resolve as well as a standard or telephoto.
• A wide aperture prime doesn’t necessarily resolve better than a good zoom, although most do, at least when you close the aperture a stop or so.
• By f5.6 most lenses resolve well, by f8 some actually are losing resolution to diffraction(depends on your camera) and by f11 most are losing resolution.
  But I realize everyone wants to know how well their new lens resolves. The AF1951 target you can find online and print for free, or whatever you are shooting, should give you a decent idea of how well the lens resolves.

AF1951 Test Chart

If you want more detail, Norman Koren has posted some downloadable test charts along with detailed instructions for using them. Or you can buy detailed (and pricey) mutiple test charts like the Edmund 58940.

Edmund Optics 58940 Test Chart

The only real necessity is to have an idea what you expect from the other lenses you shoot and compare your new lens to them. Be reasonable, though: if you think your new f1.4 prime is going to be as sharp at f1.4 as your old lens is at f5.6 you may be rudely surprised. And that new f2.8 zoom may not be any sharper in the center than your old variable aperture zoom, but it will probably toast the old one on the edges and corners. If all you are interested in is how sharp the center of the lens is then just buy Macro lenses and don’t worry about it anymore.

The bottom line, though, is checking center sharpness doesn’t help too much with testing a lens. What really helps is comparing the quadrants of the image to each other. If they elements are all aligned and centered properly the different quadrants should be similar. If the corners are soft wide open, they should all be equally soft and begin softening a similar distance from center in every direction. Similarly any chromatic aberration should be equal on all sides, not worse on one than the other (assuming your target is equally lighted).

If you look at the 4 corner targets from the lens test below, its obvious that the right hand targets are softer than the left. If you look more carefully you’ll see that the right upper is even softer than the right lower and has a bit more chromatic aberration. This is the kind of thing that will show up if the lens has an element out of center or at a slight angle. The center sharpness on the lens, though, was excellent.

The four corner quadrants of a misassembled lens. Note how much softer the upper right quadrant is than the lower left.

When you see an image like this you want to make sure the effect isn’t caused by the camera not being square to the test target, which could cause some of this effect (probably not the CA). You might try shooting the camera in portrait mode: if its alignment the quadrant in the lower left will now be in the lower right and less sharp, the upper right quadrant will now be in the upper left and more sharp. If the image looks the same in both portrait and landscape mode, its probably the lens.

Once we’ve determined that all 4 quadrants look equivalent on our fist test shots its time to run the lens through a battery of fairly quick tests:

• Near distance widest aperture. Zooms should be checked at their widest, middle, and longest focal length.
• If your zoom is variable aperture, be sure to mark down at what distance the aperture changes. You know your f4-5.6 zoom is f4 at the wide end and f5.6 at the long end, but do you know when it changes? Its good to know that shooting at 160mm instead of 170mm will give you f4.
• At each location the lens should be checked with aperture wide open, and stopped down in incremental (1/2 or 1 stop) steps to f8. You can assume the lens has reached maximal sharpness by f8. Some may sharpen further in the corners at f11, but they’ll usually start sacrificing center sharpness there.
• The same tests should be repeated at far distance.
• Testing distances will vary depending on the lens, but I find it logical to test at the distances I’m likely to shoot at. I don’t shoot the 16-35 f2.8 at 4 feet away so near testing may be 10 or 12 feet for it.
• Unless you’re going to really shoot at the minimum focusing distance, don’t test there. The lens will usually be sharper a few feet away.

Vignetting

Is really part of flat field testing but can be more obvious when the target is a smooth, evenly lit light colored wall. It doesn’t require critical line up like the other parts of flat field testing, and you simply take exposures at various parts of the zoom range and several apertures. Any vignetting should be even in all four quadrants, of course. It is often more severe at one end of the zoom range than the other, and usually less severe when as you decrease the aperture.

Distortion Testing

You can buy accurate optical distortion targets, but they’re pretty expensive ($200-$300) and for all but quantitative work there are plenty of square things you can take pictures of to detect distortion. Squarely laid brick walls work (although most aren’t as square as you’d like), big windows or doors, basically anything that gives you parallel vertical and horizontal lines. You want it to be at your level, though: angling the shot up or down (or side-to-side) will cause its own distortion. You need the camera lined up near the center of the object you’re using to check distortion.

Barrel distortion is most common at the wide end of zooms and pincushion at the long end. More complex moustache distortion may be less evident, and is less common.

The common types of distortion (above) and an example of barrel distortion (below)

More Advanced Testing

Flare Testing

Flare testing simply requires some bright sunlight. You don’t shoot directly into the sun, but have it shining at an angle from one corner of the field of view. Examine the image for ghosts and flare, and to see how badly contrast is reduced. There are no standards here, but its good to know how the lens performs with the sun in the field.

Star Test

This one requires no more than a tripod and a clear night sky. Basically you simply take a long exposure of the sky in an area with fairly uniform stars. A few second’s exposure should give you fairly pinpoint stars and several minutes to an hour will give you star trails. Observing these you can see very quickly if the lens exhibits coma or severe astigmatism, which will show as blurry stars or star trails that fatten in the corners. With such a long exposure camera sensors and noise will play a part but you can get some simple information you might not otherwise.

Image Stabilization

This is difficult to standardize for a lens reviewer, but it’s a good thing to test with your own hands and shooting style. Simply shoot a test target using different shutter speeds (making sure some of the speeds should be sharp and some blurry when handheld) with the stabilization system on and off. See how many stops YOU get with your hands. Remember IS does not work equally well on every shot so repeat several shots at each range and speed with the IS on.

Don’t try to hold the lens to a made-up standard like “if its 4 stops of stabilization I should be able to hand hold a 1/20 second exposure”. Just see if it helps and how much. Every person gets slightly different results from the same IS system. The important thing is to see how much YOU get.

What Did We Learn Today?

When buying a new or used lens, its worth an hour of time to make sure it’s a good copy and to find out a little about how it works.

My absolute requirements for an acceptable lens are:

1. Construction and function pass “look and feel” testing.
2. Front / backfocus can be corrected with microadjustment of 2/3 of the camera’s range or less (leaving a bit of margin of error for future adjustment).
3. Front / backfocus is similar throughout zoom range and at near and far focusing. How similar is a judgement call, but if it changes less than +/- 3 for a 4x zoom and +/- 5 for a 10x zoom throughout the zoom range, then I’m pretty happy.
4. All 4 quadrants of the lens are equally sharp, vignette equally, and have similar chromatic aberration at maximum and minimum zoom, near and far focus.
5. The lens doesn’t have severe loss of sharpness at one end of the zoom range or one end of the focusing range (20% decrease in resolution isn’t too unusual from the sharpest to softest part of a zoom, but 50% certainly suggests something is wrong.)

Most other things are going to be characteristics of the lens, not evidence of a good or bad copy. When you go examine your testing pictures on a monitor (no you can’t use the camera’s LCD) make yourself some notes on that lens. My notes for a made-up zoom might look like this:

• Maximally sharp at f/5.6 in center at wide end, f8 at long end
• Corners maximally sharp at f8 throughout the zoom range
• Wide open sharpness falls off at 1/2 of the distance to the corner in most of the range, but 1/3 at extreme telephoto end.
• Zoom is sharpest at wide end, begins to loose sharpness at the last 1/4 of its range.
• There is barrel distortion wide open, gone by 24mm. Slight pincushion at maximum zoom.
• The lens vignettes mildly wide open at the wide end of the zoom range, but not the long end. It disappears at f5.6.
• Image stabilization lets me handhold at 2 times the shutter speed expected from 1/focal length X crop.

The notes are specific for each lens. A wide aperture prime lens may have notes about when spherocromatism disappears. With a Macro lens, writing down at what aperture diffraction starts to cause softening may be the most important note I make, since I’m often shooting at high apertures to increase depth of field. If you only have a couple of lenses, you’ll probably throw the notes away after a few sessions with the lens, but if you shoot with a lot of different lenses like I do, its nice to have that note card to refer back to on a shoot.

Good photographers take advantages of these lens characteristics or learn work around them. They also are the fuel that feeds so many online arguments about lenses. For example, I love wide aperture primes and expect to see spherochromatism or soft corners wide open. I use them for center compositions and have learned to compose my shots to large light colored areas out of the foreground and background. But about once a week I get my feelings hurt when a renter tells me my recommendation of that lens stinks because the foreground looks magenta and the corners are soft.

Oh, and one last note. You’ll notice that nowhere in my testing do I say how to calculate “is my copy sharp”. It’s a meaningless calculation unless you have dozens of copies of the same lens like we do and are using some standard measurement of sharpness. I know, for example that on our test charts, at our standard distance of shooting, on the 5D II bodies we test with, that the 70-200 f2.8 IS II Canon lens should resolve about 20 lines/mm. The 16-35 f2.8 will resolve about 16 and the 300 f2.8 about 22 or 24. But these numbers are meaningless to your testing unless you had exactly the same set up as we do.

I also know that one copy of a lens may resolve slightly differently on one camera than another. My only point in all this is instead of worrying about “sharpest possible” just make certain its “sharp enough”. And you do that by examining your prints, not 100% magnification on your monitor. No one ever won a photo contest or award for owning the sharpest possible lens.

The copy is sharp if it resolves the detail you want to see in the prints you make. After you’ve tested the lens and know that its not defective and what its characteristics are, go take some pictures. That will tell you if the lens is sharp enough for you.

http://www.youtube.com/watch?v=iRW9AmDPqr0