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Setting Up an Optical Testing Station

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There are a lot of right ways to do optical testing. The gold standard is to put the lens on a $150,000 optical bench or run it through a well-equipped Imatest lab. But unless you have an optical bench or Imatest lab handy, that’s not practical.

We have to optically test around 400 lenses a day, which is more than our Imatest lab can possibly handle. So over the years we’ve learned a lot about practical ways to test lenses. We’ve constantly double-checked our methods using Imatest and an optical bench, refining our optical testing.

We’ve developed a simple set up that is about 98% accurate in identifying lenses that are decentered or optically misaligned. A lot of people could do this at home themselves. Certainly any camera club could make an identical setup. 

Judging from the emails I get, a lot of people want to be able to test their lenses optically and few know how to do it, so this should be useful for them. 

 

Post-rental testing bays at Lensrentals

But let me be clear about this is not, so I don’t waste your time if you wanted something else. This is not going to let you test 6 copies of a lens and determine which is the absolute sharpest copy on your camera. It’s doesn’t let you compare two different lens models and decide which is sharper. For that you do need Imatest, a bench, or just a lot of photographs.

But if you have a lens that isn’t performing like you think it should this will let you determine if the lens is optically aligned and centered properly. It can be helpful to know if the problem is with the optics of that copy, rather than the focus system, technique, or simply that the lens isn’t designed to perform any better than that. 

Nobody needs to do optical testing, of course. You can just take pictures and if you don’t like the lens send it back. But that’s not always convenient or possible. Testing is a lot faster than trying out 4 copies before you decide a lens just isn’t for you.

A Few Things Before We Start

You will need a tripod.

Some of my most experienced techs can test hand held. It usually takes about 6 months of testing 75 lenses a day before they can, though. So I recommend testing your first 9,000 lenses on a tripod. After that you can try it hand-held if you like, although you will lose accuracy.

Being Perfectly Square to the Test Chart is Required

This is the main reason a tripod is needed, although not the only reason. If you are tilted at a slight angle to the chart, you’ll get a lot of the same results you would get if the lens were decentered.

Center Sharpness is the Least Sensitive Test of a Lens

Most lenses can be pretty badly decentered before center sharpness is affected very much. Eight out of every 10 lenses we fail as ‘optically decentered’ would pass fine if center resolution was the only thing we checked. Those that do fail in the center always also fail off center.

You Can Learn a Lot About a Lens by Observing it Slightly Out of Focus

Of course, they’re blurry when slightly out of focus, but the way that they blur can be quite revealing.

Equipment You’ll Need

Here’s all you have to have:

  • Tripod
  • Test chart
  • Camera output to a computer monitor 

I don’t think I need to say anything about tripods, but I’ll go into a bit more detail on the other two requirements.

Test Chart

We’ve tried basically every type of optical testing chart that exists and by far the most useful is the ISO 12233 chart. A lot of people use AF1951 charts stuck in multiple places for testing. These aren’t completely useless, but they are very insensitive. Some fairly bad lenses look fine when you just use a bunch of AF 1951 charts to test them. Remember, they were designed to test things back in 1951.  Hopefully our standards are a bit higher today.

(As an aside, I know of several service centers that use only a modified version of AF 1951 bars to test lenses optically. Which explains why they send lenses like this back, saying they are optically fine.)

 

ISO 12233 test chart

The variable targets in each corner provide great corner-to-corner comparison, which is the most sensitive indicator of an optically decentered lens. The long gradual change in line spacing shows a lot more than the short bars of an AF 1951 chart. It also provides identical horizontal and vertical test areas in each corner. While not a true test of astigmatism, differences in the horizontal and vertical targets strongly correlate with astigmatism and other aberrations. The thick, slant-edge boxes and bars show chromatic aberration and blurring in a way an AF1951 chart doesn’t do.

High-quality ISO 12233 charts can be pricey. A good quality, 40″ wide ISO 12233 chart costs about $250. A top quality (photo paper) 60″ chart like we use in our test lab is about $700. But you can download a free version of the chart courtesy of Stephen Westin, enlarge it, clean it up in Photoshop, and print it yourself. It isn’t quite as sensitive as a professional quality chart, but it is good enough.

One thing you will want, though, is a thick black border, perfectly square, around the edge of the test chart. I’ll show you why later. If you’re printing your own, just add a rectangular border in Photoshop. If you’re buying one, it will almost certainly come with a border.

You’ll also want the biggest chart you can get. You need the chart to fill the photo frame completely when testing, so using a small chart to test a wide angle lens gets too close to minimum focusing distance for accuracy. I recommend testing at least twice the minimum focusing distance, and further away is even better.

There is one other test chart we find exceedingly useful, the Zeiss version of Siemens Star Chart, which you can buy for under $30. (Or download and print courtesy of John Williams, who has posted a pdf on Wikipedia Commons.) We only use the very center part: the black dot, surrounding white circle, and a bit of the surrounding star.

In order to keep things simple, we cut the center 2″ out of the Star chart and glue it over the existing center of an ISO 12233 chart. Sometimes we’ll add stars in the corner, too, just outside the vertical/horizontal line cross.

Lighting

Lighting isn’t critical for this kind of testing; you simply want to light the chart with reasonably bright continuous light. It doesn’t have to be extremely bright. Too much light can actually be a problem. We do a lot of this testing in live view mode and too much light will cause the camera to close down the aperture. Try your ambient room lighting before you set anything else up; it will probably be fine.

Industrial quality fluorescent fixtures will cause the usual banding problems and should be avoided if possible. If your testing area has standard fluorescent fixtures (like ours does) then you’ll need some additional lights to overwhelm the room lighting. In this case a couple of incandescent or photo-quality fluorescent softboxes are inexpensive and perfectly adequate.

A Monitor

The goal here is simply to be able to see the camera’s live view output on a decent sized, good quality monitor. For most cameras we simply run an HDMI cable from the camera’s HDMI out port to a freestanding monitor. No computer necessary. We prefer a large monitor for the comfortable working distance, but that’s just a preference, not a necessity. You could use a laptop or tablet with a high-resolution monitor, or a video monitor if you have those handy.

The HDMI output isn’t going to have resolution as high as an actual photographic image, but it’s good enough for this testing. We always confirm with an actual photographic image, of course, just to be certain. But it’s really rare that the photo shows something we missed in live view.

If your camera doesn’t have video output, or you don’t have a monitor around, there are lots of workarounds. Any tethered shooting setup will give you the same capabilities and can be run to a laptop or tablet. Built-in camera Wi-Fi or a Wi-Fi card may do the same thing, as long as it gives you live-view focusing capabilities. If your camera just isn’t capable of putting out live view to a monitor, you can try doing this using a series of photographs, but you lose a lot of information and it’s much, much slower.

Here’s a picture of one of our ‘portable’ setups, like the one I’ll bring to WPPI. (The chart is mounted in a non-portable light housing that we use for multiple purposes. We need the lighting to wash out the industrial fluorescent lighting in our building, but you probably won’t). Chart, camera on tripod, and HDMI monitor are all that is necessary.

Someone will ask if they can do this simply using the camera’s LCD. Yes, you can. But it will take a lot more time, be more prone to error, and you’ll go blind after a while.

Setting Up

Setting up square to the monitor is the final step, and it’s actually pretty quick to do. The first step is centering the camera.

1. Place the tripod and camera close to the test target, raise the camera so it’s the exact height as the center of the target and lock the column (or legs) in place.
2. Gaffer tape or draw a line on the floor at right angles from the center of the test target. Now as long as your tripod is centered over your line, your lens will be centered on the test target.

The second step is eliminating any tilt and rotation of the camera, which is also simple.

1. Center the tripod over the line you made at right angles to the test chart, at the spot where the test target fills the image on the monitor. (You should just see the black edges around the chart.)
2. Tilt the camera right or left, up or down so that the rectangle is squared. If the camera is tilted the rectangle will look like a trapezoid. (Obviously if the lens has pincushion or barrel distortion it won’t quite be a rectangle, but you get the idea).
3. Rotate the camera clockwise or counterclockwise so the top and bottom lines are perfectly horizontal

If you want to double check your final setup take a picture, download it in Photoshop and measure the length of opposite lines (they’ll be equal if the image is square) and their angle. A degree or two of tilt and rotation is fine for this work (unlike Imatest, where 0.5 degrees is critical).

If you look back at the image above you can clearly see from the picture on the monitor that we haven’t squared things yet (look at the white band outside the top and bottom of the test chart’s black box). The camera will need a couple of degrees of clockwise rotation and a bit of turning. We’re using a geared head here, but a ballhead or pan-tilt head works just fine.

Basic Testing

I’ll give a lot more examples of testing in the third part of this series, but the basics are quite simple.  The first point is that we test with the aperture wide open. Even a badly decentered lens may look reasonably good when stopped down.

For this reason you don’t want too much light on the target when testing in live-view mode: the camera will stop the lens down and override your aperture setting, making the lens look better than it really is when looking at it live. Then when you take a photograph of your test image, you’ll wonder why it looks so much worse. (If you have a question if this is happening, just walk around to the front of your setup and look into the lens barrel. You’ll be able to see if the aperture is stopping down.)

Focusing and the Center Star Chart

The star chart in the center of the test target makes it very easy to focus in live view, but first examine the pattern of the chart just out of focus at maximum magnification. On a well aligned lens the star should blur into a fuzzy oval like three of the images below do. A badly decentered lens will blur with a flare going in one direction or another, like the image on the lower left below.

If you look carefully, you’ll notice the image on the upper left has just a bit of flare going upward, toward 12 o’clock. This amount of flare can occur on some normal lenses, but the amount on the lower left is never normal.

When you get the star sharply focused, the pattern should be circular, like the image below. In some decentered lenses the gray circle, where the individual star lines blur together will be oval.  In other types of decentering, you may notice the more vertical stars are much sharper than the horizontal stars, or vice-versa.

 

I suggest taking a photograph with the center both in and slightly out of focus. Once in a while, examining the photograph will show an  abnormality of the star pattern or a flare that wasn’t obvious in live view.

Checking the Corners

Once the lens is perfectly focused in the center, it’s time to examine the corners. If you have a really good, large monitor and a camera that outputs good live view images you can  get a pretty good idea about the corners looking at the entire image in unmagnified view. Most of the time, though, you’ll be much happier doing this at 5X magnification and moving the cursor around the screen to look at the corners individually.

The idea is NOT trying to measure how well the lines resolve, especially in live view. It’s whether the lines all appear equally sharp in each corner. If all four corners look like the close-up of the ISO chart I posted above, you’ve got a great lens. No further testing is needed, go take pictures. It probably won’t, though. So let’s talk a bit about what you’re more likely to see.

Normal Field Curvature

Most lenses have some field curvature, so the corners aren’t at their sharpest when the center is in best focus. When you examine them, the corners all look a bit soft, but equally so. The second step is to zoom in on one corner and manually focus the lens to bring the corner into best focus. If you look at how far you have to turn the focus ring to get the corner in best sharpness you’ve learned something about the lenses field curvature: was the corner in best focus closer than the center, or further away? And by how much? That can be useful to know when you’re out taking pictures later.

Once any corner is in sharpest focus, move the cursor around to check the other three corners and see if they are all equally sharp again. Field curvature, which is a normal part of lens design, means the corners will have a different focus point than the center. But since our alignment is square and centered to the chart, the 4 corners should all focus at the same point. As long as they do, this part of the test is normal.

Abnormal Field Curvature (Tilt)

If some corners have sharpest focus at a different place than others, that’s not field curvature, it’s tilt. Until now I’ve been using the generic term ‘decentered’ for any lens that is optically out of sorts. In reality, there are three types of misalignment: decentering, tilt, and spacing errors. If you’re interested in the difference, I describe them here. A badly aligned lens often has more than one problem and the symptoms overlap somewhat, but we can make some generalizations.

A mildly tilted element often causes two corners to be different than the other two corners. (It can be side-to-side, top-to-bottom, or opposite corners.)

 

A lens with mild tilt. Even at 25% of actual size, the top corners are obviously softer than the bottom. In some cases, changing focus slightly you could make the top sharp, but the bottom soft. Most of the time that is not the case; even at best focus the top remains softer. Either case is abnormal.  The center of the lens usually remains quite sharp in this situation.

 

How do we tell this is simply tilt, rather than another form of decentering? With tilt, changing focus often makes the top two corners sharp, but the bottom corners will get fuzzy (or left and right, etc). With other problems, the top two corners usually never get sharp, they always remain softer than the bottom corners. But that’s a generalization that isn’t always true and really doesn’t matter unless you’re optically adjusting lenses.

More Fun with Corners

A mildly decentered lens may only have one bad corner rather than two like the example above. In that case center resolution is always still excellent, although on an optical bench or in an Imatest lab you might notice the sharpest point of the lens has moved slightly off center, away from the bad corner.

In other cases the problem affects only the horizontal or vertical line pairs, like the image below. It is subtler than the example above, but it’s still significant enough to cause a loss of sharpness on that side of a photograph.

 

A less severe problem may only affect either horizontal or vertical bars. In this image the left side vertical lines are softer than the right, but the horizontal lines are equal in all 4 corners. This lens would not be as bad as the one above, but you’d notice the difference in some images.

 

One other interesting finding that we sometimes see in this situation: by slightly changing focus you may be able to make either the horizontal or vertical lines sharp, but not both at the same time in the affected area. There are some lenses that will show this astigmatism-like behavior in all 4 corners. That’s just the way that particular lens is designed. But if only 1 or 2 corners show it, the lens has issues.

 

Changing focus slightly may change the blur from the vertical to the horizontal lines.

When All 4 Corners Look Bad

A badly tilted element, especially if near the rear of the lens, can make the entire image soft, even in the center. Spacing errors, and significant decentering of an element can have the same effect. Sometimes a decentered element leaves the center of the lens quite sharp, but all 4 corners very soft.

The question becomes how do you tell if a lens has a significant optical abnormality, or it’s just a bad design that is soft no matter what copy you have? Usually when this happens, the lens is so bad you don’t need any kind of testing to see the problem. There are halos, you can’t identify anything in the image, the camera won’t even autofocus with the lens, etc.

It’s rare, but there are cases where all 4 corners are bad, or the entire lens is somewhat softer than it should be, but not so bad as to be immediately obvious. A little common sense helps in this situation. You should expect 10X consumer grade zoom to be rather soft at the long end. An f/1.2 lens is probably going to have slightly soft corners at widest aperture. Even good telephoto zooms often have soft corners at the extreme telephoto end.

There are several things that help identify the ‘optically bad copy’ from ‘badly designed lens’ in this situation. First and foremost is the center star target. A lens decentered this badly will almost always have a significant flare, like we demonstrated above, when just slightly off focus. Some will even show flare at their best focus. If you examine the corners carefully they may all be soft, but one is usually quite a bit better than the others, and one quite a bit worse. Examining the thick black boxes will often show chromatic aberration at the edges and it will be of odd pattern: It might be away from center on one side and toward center at the other, etc.

If you’re still not certain, retest the lens with the aperture closed down 1 stop. Obviously all lenses will be a bit sharper stopped down. But with an optically decentered lens you’ll usually see some corners get much sharper stopped down than others, and the pattern will look like the ones we’ve described above.

I want to emphasize that this ‘all over’ or ‘all corners’ softer decentering is really rare. Out of every 100 decentered lenses,  we find 2 or 3 of them have this kind of pattern.

Limitations

Zoom lenses have to be checked at 2 or 3 spots. Most optically challenged zooms are bad throughout the range, but there are definitely some that only have a problem at the long or short end. Obviously you have to move the tripod to reframe the image at a different zoom range and realign the camera, but that shouldn’t take more than a few minutes.

Because of the limitations of chart size, testing at a given focal length is only done at one focusing distance. There are lenses, although they are rare, that have problems at certain focusing distances but not others and this test might miss that problem. But optical benches and Imatest have the same limitation; they only test at certain distances. You can overcome that to some degree by making charts of different sizes, but that’s a lot of trouble to go to for something you’ll probably never see.

One thing I should note: this test may over read a bit, particularly on wide-angle zoom lenses and large aperture, wide-angle prime lenses. Most of these have a little bit of flare in the center even when perfectly adjusted and all 4 corners will rarely be completely identical, although they should be close. If you look carefully enough, for example, you’ll see slightly softer horizontal or vertical lines in almost every copy of a 16-35 f/2.8 zoom or a 35mm f/1.4 prime shot wide open.

That’s one reason I suggest this testing setup for a camera club. If a friend brings another copy of the lens, you’ll feel a lot better comparing yours to his when you have a question, and you should be able to do that in 10 minutes.

Summary

A lens that’s optically awful, bad enough to affect sharpness everywhere, will generally show a lot of flare of the Siemens Star in the center when slightly defocused. All four corners may be blurry, but some corners will be worse than others, or the horizontal and vertical resolution will be different.

Less severely decentered lenses may look fine in the center and may, or may not, exhibit center flare. They will show differences in the corners that are readily apparent, however. If a lens has no flare in the center and the corners of the ISO 12233 chart all look identical, it’s optically fine.

We’ve been testing exactly this way for several years, identifying 60 to 70 lenses a month as decentered. We retest all of those on an optical bench and rarely find one that was actually OK. In other words, the test is nearly 100% specific. If it says a lens is decentered, it’s almost certainly decentered.

We also run QA checks using Imatest or the optical bench on lenses that have passed this optical testing. When we recheck these lenses, we do find that about 0.5% of  are actually decentered. However, if we repeat this optical chart test on those same lenses, they almost always fail the repeat test. In other words human error, not the test itself, let the bad lenses pass.

There are lots of other ways to test lenses, of course. But we’ve tried most of them and this is by far the most accurate in our experience, short of setting up an Imatest lab. And testing 8,000 to 9,000 lenses a month, experience is one thing we have a lot of.

The next article will be a few days in the making, but we’ll have a lot more examples of problem lenses, and will probably do a simple optical adjustment using nothing but this test system.

Roger Cicala

Lensrentals.com

February, 2012

 

Addendum:

If you read this post and thought, “Yeah, I know that,” Midwest Camera Repair is looking for an experienced Lens and D-SLR tech, mainly to service Nikon Lenses; knowledge of Canon lens would be helpful but not required. Someone who has experience servicing high-end lens would be best.  Most of our repairs are middle to high-end equipment to Professional customers.  We will train on use of Nikon & Canon test and adjustment equipment.  Our Nikon lens volume has more then doubled in the last year.  Knowledge of D-SLR repair would also be helpful.

Midwest is a Nikon Authorized Service Center and one of only four authorized, trained and equipped to service the VR-Series lens.  They are also authorized on Canon IS-Series lenses.

Send confidential resume to repairs@midwestcamera.com

 Again, this is a posting for Midwest Camera Repair, because they’re good guys and do a good job. It’s NOT a lensrentals job posting.

35 Responses to “Setting Up an Optical Testing Station”

Aaron said:

And now Imatest has put you on their crap list because you have shared the secrets that keep all* of us from buying their excellent test suite.

*And by all, I mean some rental shops or people with far too much money and free time

LensRentals Employee

Roger Cicala said:

Aaron, you know tons of people will still want Imatest because they want the numbers!

And, of course, I’m one of them :-)

Nqina Dlamini said:

Still digesting these article. Again thank you for this.

LensRentals Employee

Roger Cicala said:

Andreas, it’s too coarse and doesn’t have the black circle/white ring in the center. It would probably be a simple matter for someone to make a good vector image, but I don’t have the skills.

LensRentals Employee

Roger Cicala said:

John,

The largest charts from Imatest are what we use (exactly what you linked to). Semi-gloss is a bit higher resolution but in a lot of lighting situations will glare which makes the test difficult. If you’re going to light with some softboxes the semi-gloss is great but if you’re just using ambient light (or will be taking it to different locations) I’d go with the matte finish.

There are lots of other vendors but I think Imatest usually has the best prices and they always ship immediately. I’ve gone to backorder hell in a couple of other places.

Roger

Carsten said:

Recently, I used the following method for setting up the camera so that the sensor plane is exactly parallel to the plane of the test chart: position the camera on a tripod in front of a mirror and then adjust the camera so that the center of the lens is visible exaclty in the center of the image (using live view). Then tape the test chart onto the mirror.

What to you think of this method?

What I actually found in my test was that there was a severe amount of chromatic aberration, even in the center, especially on vertical lines, with differences between the left and the right of the image: cyan / magenta on the left, blue / yellow on the right. The amount of CA on the left was more severe than on the right, so that the image on the left really looked unsharp. The CA is even slightly visible in a nearly focused image of a Siemens-Zeiss test star (cyan flare to the right, magenta flare to the left of the small black drop).

I hope to learn about the reason for this kind of CA in your next posting (which you will hopefully publish soon, as I am close to returning this lens (Micro-Nikkor 105mm 1:2,8G)).

Mark K said:

Roger,

Great article… Thanks!

You state that you shouldn’t be using fluorescent lighting for this test, but then you test box obviously has florescent lights. What’s the difference between the house lights and the lights you use in the test box?

Mark

LensRentals Employee

Roger Cicala said:

Mark, the industrial fluorescents in the ceiling are low frequency and cause a lot of banding. The fixtures are high frequency and while they can still cause problems at certain shutter speeds, it’s a lot less of a problem. You can see in the image, too, that we keep the fixtures plugged into a power strip so we can turn them off or on as need be depending on lens aperture, etc.

LensRentals Employee

Roger Cicala said:

Carsten, back when we started I tried the mirror thing, used a laser, plumb line, etc. I never got very good results with any of them, even when I sent off for an ‘optical quality’, front surface mirror (using a glass fronted mirror is hopeless). The photoshop trick is a lot simpler, quicker, and more accurate. Imatest, where exact lineup is very critical, builds that check into the software.

While the 105 Micro Nikkor has some CA, the things you’re describing are pretty bizarre. Certainly sounds like that lens has issues!

Roger

Samuel H said:

Great article.

One question: why the hesitation to call it astigmatism? From my understanding, if horizontal and vertical resolution is clearly different, the lens has astigmatism, though not every lens with astigmatism will have different horizontal and vertical resolution (it can be aligned exactly at 45º). What am I missing?

Walter said:

I discovered something interesting with my Nikon 80-400 AFS related to the VR system that relates to this sort of thing (decentering).

I first did the test using my D7100′s phase detect AF. I set the lens to 400mm f/5.6 and focused on a test target (some high contrast printed text on a wall), then swung the camera left to right, taking an exposure using a strobe as the test target crossed the center of the frame. The image was extremely sharp with no problems. I then repeated this, swinging the lens right to left, top to bottom, and bottom to top. All images came out sharp.

Then I turned on the 80-400′s VR system (set to “Normal”) and repeated the test. Every time, there is asymmetrical yellow/blue chromatic aberration in the direction of motion: the black text has a blue fringe in the direction of motion, and a yellow fringe away from the direction of motion. For instance, moving the lens from right to left while taking the shot gives a blue fringe to the left and a yellow fringe to the right, while moving it from left to right reverses the fringes.

Clearly the VR system is doing something here to cause this. The obvious candidate is decentering (since it’s an asymmetric aberration in the middle of the frame), and the obvious explanation is that of *course* there are decentered elements: the whole point of the VR system is to decenter a couple of elements in such a way as to shift the image on the sensor opposite to the camera motion. But this isn’t perfect, and there are residual asymmetric aberrations resulting from the decentered elements in the optical path. The orientation of those aberrations ought to depend on the orientation of the decentering (tilt or shift) of the elements, which in a VR system will depend on the direction of the motion it’s trying to compensate for.

This is in no way a complaint about the VR on this lens, which is truly excellent: if I find an owl at dusk and I have no tripod a little fringing is a small price to pay for being able to get a shot at 400mm 1/30s handheld. But I think this explains the conventional wisdom of “turn your VR off if you don’t need it”, which is borne out by my field experience.

I should add that I shot Olympus 4/3 for years, and saw no such image quality penalty from the in-body IS, which is exactly what you’d expect: moving the sensor around doesn’t decenter anything.

LensRentals Employee

Roger Cicala said:

Samuel,

Technically, to test for astigmatism rather than having vertical and horizontal lines, we should have sagittal (from center to corner) and tangential (at right angles to sagittal) lines. We’ve actually cut up an ISO 12233 chart, rotated the corners so they were aligned that way, and could then say we did it right. The results were the same, so I feel this is the same thing, but I didn’t want someone to come smack me around for using the terms improperly :-)

Roger

Samuel H said:

Oh, the smackers… Thanks for the explanation :)

neuroanatomist said:

Great info, thanks!

The Imatest offerings are definitely economical (relatively). I use the Applied Image QA-77 charts, which are enhanced versions of the ISO 12233 chart that still meet all the criteria of the standard.

http://www.aig-imaging.com/mm5/merchant.mvc?Screen=PROD&Store_Code=AIIPI&Product_Code=QA-77&Category_Code=Imatest

I ran across Applied Image in my day job – they have some nice standards for testing/calibrating microscope imaging systems. Incidentally, I’ve used one of their microscope slide standards (ISO 3334/NBS 1010a) to test the resolution of macro lenses including the MP-E 65mm.

Lasse Beyer said:

Oops, didn’t notice that it’s actually linked already in the article. Didn’t check the link because of “enlarge it, clean it up in Photoshop” which made me think of a JPEG file. There’re a PDF and a SVG for download though, which are vector files and scale up pretty well, so no need for Photoshop at all.

Dave said:

Roger, it seems to me that you may be better equipped to evaluate and adjust lenses than the Canon service centers. Have you thought about adding lens adjusting as an additional service to offer to customers? Personally, I’d rather send my suspect lens to you for evaluation/alignment than to Canon.

LensRentals Employee

Roger Cicala said:

Dave,

I am considering an evaluation service. I’ve purchased some very high-level optical equipment that should be arriving in April and May (this kind of stuff is built-to-spec after ordering). When I get some large numbers run through them and an idea of how quickly and accurately tests can be done, I’ll probably offer testing as a service, but it’s at least 6 months away. The way we do things now is accurate, but so time consuming that it wouldn’t be reasonably priced (hence I try to put the methods out so people can do it themselves).

Roger

Dag said:

Dear Roger,
I am thinking to make a print via bayphoto with the iso Chart on it. The Price is good for a 40 x 30 Print 45 USD if you spend additional 33 USD you get it on a 2mm styrene board. Is there anycause why I should not do this ?? Thanks a lot Dag

Yohan said:

Bob Atkins posted a similar method to test for distortion. Instead of printing a large image he suggested using a peg board and pasting printouts in the center and corners (he used a modified AF1951, though one could use the ISO 12233 posted in the article).
I also pushed a long rivet/screw through a hole in the middle of the peg board as a means of determining if the camera sensor plane was orthogonal to the peg board (assuming the rivet itself was at 90 degrees from the peg board and the peg board is flat). I suppose you could do the same thing with a push-pin if your chart is mounted on a foam poster board–just make sure the pin is in the center of the live-view screen and that you can’t see the side of the pin, only the head. I’m not sure if that would be faster than confirming if the border is rectangular vs trapezoidal.

Yohan said:

Oops, I meant “parallel” above, not orthogonal. :(

LensRentals Employee

Roger Cicala said:

Dag, no reason I can think of. Sounds like a good plan.

Max said:

Roger, You guys are using a center column tripod extended that high up to Imatest?

Oh, the humanity and all the photographers screaming around here. I told you, I can’t even talk to people whose friends are on there. Ah! It’s–it’s–it’s–it’s … o–ohhh! I–I can’t talk, ladies and gentlemen.

LensRentals Employee

Roger Cicala said:

Not that high for Imatest, the Imatest charts are lower. We also lowered the tripod legs and raised the column to give a better shot of the ISO 12233 chart. But extended center column to some degree on Imatest? Sure unless it’s a big telephoto lens. I’ve done them on solid carts and tripods without center columns, run serial same lens tests and large batches of lenses. There’s no variation difference with a solid center column extended several inches. And without an extending column centering properly is impossible. Centering is too critical with Imatest to compromise.

Max said:

In my experience both the chart and the tripod need to be isolated from any environmental forces. As an example, some suspect results I had last summer were the result of running the tests while the AC cycled on and off. The vibration of the blower fan was transmitting to the floor for the tripod and/or walls where the test board was mounted. Since then, I turn off the HVAC while conducting tests. And of course the A7r shutter really throws wrenches into testing. I have felt the shutter activate through the soles of my barefeet at times.

LensRentals Employee

Roger Cicala said:

Max, I totally agree. We keep rubber dampers under the cart wheels, an isolating/leveling plate between the tripod and head, etc. And still get the kind of effects you’re talking about. I lost a day’s testing when someone 200 yards away was jackhammering and occasionally will lose a test when a large truck goes by.

The optical benches are all on air cushioned legs for the same reason. But we’re also set up on a 12″ concrete slab floor, so things like AC don’t have much effect.

BTW – you do realize the tripod / head in the picture is for this testing system, not for Imatest, right? This is much less sensitive to that kind of thing. I’d never get by with a simple Gitzo tripod for Imatest.

Max said:

Great post!

Peter Figen said:

Would there be an advantage, say, to print four 60 x 90′s on an 11880 and mount those to a wall in order to get further away from the target and still fill the frame. The problem I’ve always seen especially with wide angle lenses is that the testing is done at distances that are not at all close to how you’d be using the lens in the real world. And you have those floating elements coming more into play the closer you get as well. Printing large targets yourself or on a friend’s printer is ridiculously inexpensive.

LensRentals Employee

Roger Cicala said:

Peter,

I think if you printed the parts of the chart so that the proportions were similar, that would work. But the line pairs need to be in proportionate size. So a 60X90 of each corner and one of the center, etc. would work.

Peter Figen said:

If I understand you correctly, I would split the pdf into four quadrants and print each one of those at 60 x90, then attach all four to the wall together as if it was one giant version of the original. That should, also, if I’m not mistaken also minimize the effects of not being perfectly square, setting up against a ten foot by fifteen foot target. That should also minimize the effect of the (slightly) reduced resolution of an inkjet as opposed to an imagesetter output.

I’ll probably start with a single 60 x 90 print and see where that goes. I’ve actually got only one lens that I feel is not all it could be (Canon 24-70 2.8 II) and this will hopefully provide some good data for Canon to work with.

When I do get to taking this to Canon, do you have any idea if it’s better to drop it at the Hollywood CPS center or drive it down to Irvine. Hell, Hollywood might send them to Irvine anyway, but I don’t know.

Thanks again for all you do to educate us out here, wherever we are.

Peter

LensRentals Employee

Roger Cicala said:

Peter,

That sounds like it should work perfectly. I don’t know much about the West Coast Canon repair center, so I can’t help you with that, I’m afraid.

John Leslie said:

I was interested to just find I can easily download a service manual for my GH3 from the Internet (Google DSC1211041CE). As the GH3 comes in some kit options it includes info on pulling the included lenses apart (in considerable detail). Is this normal for manufacturers? Will there be Canon ones out there too?

Max said:

Roger, most of what I learned from Imatesting came from you.*

*Except the 100s of ways I figured out how to do it wrong.

LensRentals Employee

Roger Cicala said:

Max, LOL. I should have written the article “Why it took me 6 months to figure out how to use Imatest.” I went through way more than 100 wrong ways, that’s for sure. And now 4 years later, I’m still tweaking things.

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