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06-29-2014, 11:06 AM   #1
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Lens quality variation?

Is it common for some lenses to be better than others that are seemingly identical? I read in many posts about getting a "good copy" of a certain lens and it makes me wonder why one particular lens would be better than another one. I suppose I've answered my own question when I compare lenses to cars coming off an assembly line, but you'd think the QC would be much better in a lens factory. Hmmm.....

06-29-2014, 11:25 AM   #2
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QuoteOriginally posted by Dewman Quote
Is it common for some lenses to be better than others that are seemingly identical? I read in many posts about getting a "good copy" of a certain lens and it makes me wonder why one particular lens would be better than another one. I suppose I've answered my own question when I compare lenses to cars coming off an assembly line, but you'd think the QC would be much better in a lens factory. Hmmm.....
QC at the factory is just fine. It's what happens between the factory and the consumer. Even then most lenses sent in for adjustment are found to be within specification.
06-29-2014, 11:34 AM   #3
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Copy variation is a much discussed topic and I've no doubt it exists. How much difference between copies can depend on a number of things including:
  1. The quality of the lens. Kit lenses for example are made as cheap as possible so it is likely there will be more variation. The Limited line or the * line should theoretically have less variation.
  2. The manufacturer's quality control. Theoretically OEM's like Pentax, Nikon, Canon should have tighter standards than third party makers. Not sure if this is actually true, but many reports of people returning 3 even 4 copies of a Tamron before getting a good one. Sigma also used to have a reputation for wide variability between copies but based on comments that seems to have improved recently.
  3. The design of the lens itself. Some lens designs are easy to get aligned correctly, some have design issues that inherently make QC more difficult.
  4. The camera the lens is mated to. The way I understand this is that both camera and lens will have a tolerance specification. Say +/- 10. If the camera is at zero and the lens is at zero then, wow, you have a great copy of that lens. But give it to someone else with a camera that is -10 and suddenly it is a crap copy. It also works out if for example your camera is at +5 and you get a lens that is at -5, again, wow you have a great copy but put it on a camera that is -5 and now you have a crap copy.
  5. Age / use of both camera and lens. Both might be perfect from the factory but knocked around for a couple of years? Things can get miss adjusted.
  6. Shooting style. If you are shooting wide open with a lens most of the time you will see slight variations that someone who mostly shoots stopped down will never notice.
  7. Individual shooters skill. Let's face it there are folks out there you can hand a poor kit lens to and they will find a way to make a good image. And you can hand me a perfectly hand tuned camera / lens combo and I will still shoot garbage.
  8. How the test was conducted. I don't give much credence to claims when the shots are hand held, in poor light or just not conducted scientifically. Put the camera on a tripod, in good light with a proper test target and then we will talk.


There is copy variation and that's why most of the newer and higher end bodies allow in camera adjustment for lenses. This allows fine tuning in the field to make up for any variation from the factory.
06-29-2014, 12:17 PM   #4
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QuoteOriginally posted by jatrax Quote
Copy variation is a much discussed topic and I've no doubt it exists.
Yep. There is QC, transportation, how the sellers/distributes handle it, etc. But there is also what is also user error. Sometimes people get a nice lens and expect all their photos to look like National Geographic. Then they blame the lens when it doesn't do that for them. Sometimes they ruin the lens themselves, without realizing it.
You need a good lens, but you also need to know how to use the lens and camera, how to capture the scene, tell a story. That's the hard part. Ive taken very sharp photos with great contrast and details with my DA 35mm f2.4 (which can now be found for ridiculously low prices), but they were still boring photos. But when I first got the lens, my photos with it weren't nearly as sharp. So even to get the most out of the optical quality of a lens you need some time and practice.

06-29-2014, 02:55 PM   #5
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Copy to copy variation does occur but I feel most of it is from mishandling in the used market. The variation from the factory is caused by deviations in the glass grinding process, lens barrel machining and camera body lens mount face. Even Leica rejects lens elements at the end of the grinding process. I have been there and have seen it. No optics company seems to be able to control their manufacturing processes so well as to not need inspection after the fact. So, a really tight inspection process becomes necessary. Companies with average process controls and an average inspection process will have escapes of product that is unacceptable to the customer. The reliance on inspection in the world of QA has never been the solution for high quality. The solution is to have all of the manufacturing processes under strict control via statistical control charts that can be used to flag any special causes that need to be corrected. The difference between a high quality optics firm and an average one is the degree of dimensional variation accepted by management.

Last edited by desertscape; 07-01-2014 at 10:04 AM.
07-01-2014, 05:42 AM   #6
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The only issues I've ever had have been with what I assume to be centering, as in equal sharpness across the frame. Unless you have two of the same lens models, it's difficult to recognize minor sub-par overall performance, but every sensor has four corners, and finding a lens with even approximately identical performance in every corner is amazingly difficult. Somewhere around 50% of the digital-era lenses I've owned (at least briefly) have obviously failed in this regard, and not just with Pentax, but other brands too. Obviously most of us have better ability to test now than we did years ago, so to what extent the problem is worse or we're just seeing it more now, I'm not sure. I think most purchasers just assume their lenses are ok and never reject defective lenses, because they don't test them thoroughly enough. Sometimes it's just that last 10-20% at one edge or corner that fails, and you really have to look for that, especially if you normally don't care about the edges of a frame.

I'm not buying the shipping damage story; I think this is purely a quality control issue, especially with lenses that aren't optically stabilized.
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