Bad Times with Bad Filters

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A long time ago I wrote a blog post called Good Times with Bad Filters about how cheap UV protective filters are different from good ones. It was mostly in fun.

Today I’ve got a post about how cheap UV filters may hurt your lens. It’s not in fun.

Here at Lensrentals we see lenses come back with scratched front elements every so often. Not a big deal, it happens. But since the Canon 24-70 f/2.8 Mk II lens came out we’ve seen a whole lot of them come back with scratched front elements. The weird thing was it was always in the center of the lens and often circular in pattern like the one below. (Ignore the dust, this front element had been taken out for replacement and sat on my desk for an hour before we took the picture.)

 At first I thought maybe there was a problem with the new coating Canon was using, but it seemed a coating issue wouldn’t occur just in the center.

It turns out that the combination of the slightly bulging front element of this lens and a ‘less than best quality’ thin or ultra-thin filter is the culprit. Let me make this point first, though: The vast majority of filters do NOT touch the front element of this lens. I went through a number of filters before I found one that did. But it can happen and that’s worth knowing.

This 24-70 had a front element that was about to be replaced because of some scratches near one edge (which is why I didn’t mind putting filter after filter on it to see if any caused a problem), but the center was absolutely clear.

 I went through 8 filters with absolutely no issues. The 9th filter, though, seemed to come in contact with the front element. It’s hard to be certain about that by just looking and feeling. So I dusted on the back side of the filter with a little carbon black. Notice I covered a fairly large area of the filter with it.


Then I put the filter on the lens, took it back off the lens, and took a picture of the front of the lens. Notice the circular pattern of the carbon,which is fairly clingy. Other than a few specs, it doesn’t come off the filter except where there was glass-to-glass contact. This is a much smaller area than the large smear of carbon I put on the filter.

And when we blew the carbon off the lens, there were a couple of scratches that hadn’t been there before.


This is a good demonstration about what MIGHT happen. I will add that I’ve put another dozen brand name filters (Heliopan, B&W, etc.) on this lens with absolutely no problem and no sign of glass-to-glass contact. It seems that you need the proper combination of a thin-line filter with glass close to the back of the filter, and a lens with a slightly bulging front element (this lens has one, but so do lots of others) to even worry about it. I would also think that wider front elements (this is 82mm) might allow more play or sag in the center making this more likely.

For those of you who can’t wait to go post something about how the Canon 24-70 f/2.8 II has a problem, let me assure you that’s not the case. I had to try a number of filters and the one that I used in the demonstration is a ‘discount’ filter that someone sent back to us in place of the name-brand filter we sent them. The other name-brand filters I tried were all fine.

I’ve also seen this ‘center circular’ scratch pattern on a few other lenses and we’ll start watching for it now that we know what it is. But I don’t have enough records to go back and figure out which of the numerous front element scratches we’ve seen were of this type.

My suggestion, though, is that you stay away from ultra-thin filters on these lenses, especially discount ultra-thin filters. If you look across the front of your lens from the side, you can get an idea how far up the center of the lens bulges. Then look at the back side of your filter and see how far the glass is from the bottom of the threads. If those two distances seem similar – well, be careful!

Roger Cicala


October, 2013

There Is No Perfect Lens Test, Either

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In my last article, I wrote about the fact that every copy of a given lens has some bit of sample variation. This affects lens reviews, whether lab-based or photography-based, because the copy they tested will be just a bit different from the copy you buy. I suggested, that if you want to get a feel for what the lens you purchase is likely to be like, you had best compare several different reviews. That should give you an idea of the variation that exists.

Photographs are really the best way to evaluate a lens’ performance, but you have to look at a few dozen, minimum to do it. That takes a lot of time and a fair amount of bandwidth. Looking at online size jpgs is worthless unless all you do with your images is post online-size jpgs. You need to download at least full-size jpgs (preferably RAW files) and look at them at 50% magnification to get a good idea about a lens’ performance.

Lab testing, with its numbers, gives us nice, quick overviews of lens performance. It’s useful for lens reviews so that you can compare one lens to another. It’s useful for people like me who have to test lenses to make sure the optics are OK, since it eliminates some of the human variability that comes with looking at images of a test chart.

But each type of lab test has its own strengths and weaknesses that nobody ever talks about. This is important if we’re going to compare several different reviews of a lens, because we should have some idea of what the reviewers are actually analyzing. Like every scientific test, if you don’t have a grasp of the testing methods being used, you can’t possibly understand the results. Continue reading

There Is No Free Lunch, Episode 763: Lens Adapters

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Lens adapters can be useful things sometimes, letting you mount one brand of lens on another brand of camera.

One thing that has always bothered me, though, is the idea of doubling the number of lens-mount interfaces. When you look at the thick metal pieces on the front of the camera and the back of the lens, and then consider that they have to be lined up exactly parallel to the image sensor, it’s kind of amazing it works. Continue reading

There is No Perfect Lens

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The Three Questions

I get asked a couple of questions every time I publish a graph showing Imatest results for multiple copies of lenses like the one below. Most people understand that some copy-to-copy variation is inevitable in the manufacturing process. Most are surprised, though, at how large the sample variation seems to be. Heck, I was surprised at how large the sample variation was when I started doing this kind of testing.

The three questions I get asked over and over are the same questions I asked myself when I first started seeing these results:

  1. Are you sure the variation is that great?
  2. Can you really see the difference in a photograph?
  3. Can optical adjustment make the copies with the worst results better? Continue reading

Lensrentals is Coming to Nashville!

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We are happy to announce the opening of our satellite location in the Nashville area. Our Nashville office will serve as a pick-up center beginning on September 12th. There is no charge to pick-up from the Nashville location. Initially, all Nashville orders will be available the next day, although we hope to soon offer same-day pickup for our most popular items. Continue reading

What’s All This RAW Hack Business?

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You’ve more than likely heard about the Canon 5D Mk III RAW Hack. We too have been keeping a close eye on the Magic Lantern (ML) team as of late. In the last 4 months they’ve enjoyed their greatest triumphs since initially cracking the 5D Mark II’s code almost 4 years ago. It’s been a wild ride, and even though it’s far from over, we’re ready to join in. The LensRentals crew has been independently testing the various new firmware builds all summer long and we feel it’s now safe to recommend them to our customers.

Fig. 1: Artist rendering of what the Magic Lantern team might look like. Continue reading

Fun with Color Vision

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I’ve been doing a lot of technical things lately, writing up our repair data and investigating methods of reducing optical variation in lenses. So I thought I’d take a bit of a break and write a post about something fun. Human vision is always fun to me, since it’s an area where I can apply both my photography and medical experience.

Most of you probably know some of these things, but I bet most of you don’t know all of them. So I would recommend skimming along this rather long post to find the topics that interest you. Since it covers (among other things) carrots, advertising, Impressionist painting, evolution, optical illusions, and warship camouflage, there ought to be something of interest somewhere. Continue reading

Lensrentals Repair Data: 2012-2013

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Correction: Lenses called “Rokinon” in the “Weeks to Failure” rate incorrectly included Bower & Samyang branded products. Because of this error, data for lenses called “Rokinon” lenses has been removed. We apologize for this inaccuracy, and any confusion that may have resulted therefrom.

What Is This?

We have a unique opportunity: We own a very large number of lenses and cameras subjected to rather harsh conditions. Basically, we have a laboratory set up to stress test photography equipment and we share those results with you.

Our numbers reflect heavy and hard use. Your personal equipment shouldn’t fail nearly as often; it isn’t subjected to rental conditions. But this does provide some comparison about how fragile various pieces of equipment are.

It’s not completely scientific, but with data on over 12,000 copies resulting in over 2,000 repairs it’s a bit more useful than posts on a forum going back and forth between “mine’s great” and “mine sucked.”

This list is not a comment about how good a lens is. It’s simply data about how often it breaks under harsh conditions. Some of my favorite lenses and cameras are rather fragile. Continue reading

Good Vibrations: Designing a Better Stabilization Test (Part I)

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My name’s T.J. Donegan, I’m the Editor-in-Chief of DigitalCameraInfo.com and CamcorderInfo.com (Soon to just be Reviewed.com/Cameras). We recently wrote about designing our new image stabilization test for our Science and Testing blog. I showed it to Roger and he asked for the “nerd version.” He was kind enough to let us geek out about the process here, where that kind of thing is encouraged.


DigitalCameraInfo.com’s latest image stabilization testing rig. (In beta!)


Since the beginning of DigitalCameraInfo.com and CamcorderInfo.com, we’ve always tried to develop a testing methodology that is scientific in nature: repeatable, reliable, and free from bias. While we do plenty of real-world testing during every review, the bedrock of our analysis has always been objective testing.

One of the trickiest aspects of performance to test this way is image stabilization. Things like dynamic range, color accuracy, and sharpness are relatively simple to measure; light goes in, a picture comes out, and you analyze the result. When you start introducing humans, things get screwy. How do you replicate the shakiness of the human hand? How do you design a test that is both repeatable and reliable? How do you compare those results against those of other cameras and the claims of manufacturers?

Continue reading

Silent Changes

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Every so often I get an email asking me to jump in on some forum argument or other. I rarely do that because of the language barrier.

Two of the common languages spoken on forums are CAKWAF (Complete, Absolute Knowledge Without Any Facts) and AFIDAWAB (Any Facts I Don’t Agree With Are Bullstuff). Since I am not fluent in those languages, I tend not to get involved in the more, uhm, enthusiastic online discussions. But sometimes I can’t help myself, repeating the behavior of adding facts to a ‘vigorous’ discussion and always expecting a different result.

This happened recently when a discussion occurred about what the original poster called ‘silent upgrades’ to lenses. As someone who takes apart lenses and cameras for my day job, I did confirm to that person that over the lifespan of a lens, some internal changes may occur and the camera companies don’t make announcements about them. (I don’t like the term ‘silent upgrade’ because such changes aren’t always an upgrade, it may be something as simple as a new vendor supplying a slightly different part. There also seem to be times when the change is actually a downgrade.)

Most of the responses to my statement were written in CAKWAF and AFIDAWAB. Responses claimed with absolute certainty there were laws that prevented any changes once a lens was released unless they were announced (there aren’t). Other people, based on owning two different copies of a certain lens, stated with absolute certainty there were never any changes in the 10-year production cycle of that lens (there were, I’ve seen them). Rather than responding with words, I thought it would be simpler to just take apart a couple of lenses.

The Canon 85 f/1.8 is a very good, reasonably priced lens that’s been popular for two decades. Its external appearance and optical formula have been unchanged for that entire time. It also has a tendency to get dust under the front group, so (because we’re a rental house and people expect to rent clean lenses – not because the dust mattered to photographs) we take them apart to clean them quite often. So here are two copies of the Canon 85mm f/1.8 with the front group removed for cleaning. One of these things is not quite like the other.


A 6-month old Canon 85mm f/1.8 (left) and an 18-month old copy (right).


While identical on the outside, identical optically, and identical in function, the newer one seems to be missing a circuit board. Notice the slot that the connecting wires go through on their way to the main PCB (circuit board) on the back of the lens is still there. There just aren’t any wires going through it.

If we take the mount of the two lenses off, we can see other differences in the PCBs.


A 6-month old Canon 85mm f/1.8 (left) and an 18-month old copy (right).


Obviously the newer version doesn’t have the 5 soldered wires coming up from the accessory board (6 o’clock on the older version) because the circuit board isn’t there. The new PCB board doesn’t even have the solder points to attach those wires and there are some other minor differences in the circuit traces on the PCBs. I didn’t take the PCBs out to show you the bottom side, but if I had you would notice that all the functions of the DC/DC conversion board (the board missing from the newer copy) have been added to the main PCB in the newer copies.

Does it make any difference whatever in how the new copies work compared to the old copies? Nope. I suspect it’s simply that advances in electronics since the lens was first released make it simpler and more cost effective to eliminate the secondary DC/DC conversion board and incorporate those functions into the main PCB. It hasn’t been done to address any reliability issues (the 85 f/1.8 is a rock, it  hardly ever breaks), it doesn’t change function at all, it’s probably just more cost effective.

Sometimes changes like this that occur during the life of a lens (or camera) are done to address a problem. I can think of a half-dozen examples off of the top of my head; a few announced by the manufacturer but most not announced.

These aren’t always ‘secret upgrades’ as the paranoid among us like to think, but sometimes they are. Most often, though, they’re simply a change in subassembly supplier or a more effective way to manufacture a part, like this one.


Roger Cicala


July, 2013