Quantifying the Variation in Sharpness Between Copies of the Same Lens

As you might know, different copies of the same lens can vary in quality, and some people go as far as to purchase multiple copies to pick the sharpest one before returning the others. Roger Cicala over at LensRentals wanted to quantify exactly how much variation actually exists between copies of the same lens, so he subjected some to Imatest quality tests:

[…] while the Canon 100mm f/2.8 IS L lens is a bit sharper than the other two on average, not every copy is. If someone was doing a careful comparative review there’s a fair chance they could get a copy that wasn’t any sharper than the other two lenses. I think this explains why two careful reviewers may have slightly different opinions on a given lens.

That’s interesting to think about. Two highly objective reviews of the same lens could come to different conclusions about relative sharpness compared to other lenses, simply because there are differences among copies of that lens. Too bad reviews are usually based on a single copy of a lens, rather than the average performance of multiple copies.

Notes on Lens and Camera Variation [LensRentals]

  • Anonymous

    I am part of those people, using Imatest for comparison. I have indeed tested sub-par lenses. If you do not have two or more identical copies of the lens, it could be difficult to know that with certainty.

  • Blueeyedpop

    Variations in the melt of the glass lead to differences in dispersion and refractive index. 
    Variations in center thickness lead to slight variations in power of the individual elements.

    These variations are accommodated by changing internal air spacings to bring a lens within saleable tolerances. Some lenses just are that good, others not so much. Some will be rejected and likely scrapped. 

    In the motion picture industry, Zeiss primes have slight overall variations in focal length, and their focal scales are coded according to which focal length band they fall in, so that their marks come up accurately. Panavision will make custom mechanics to accommodate variations in the glass of a particular lens.

    In the end, there is still a lot of variability.

  • Anonymous

    Great article.
    I had heard a little about how different lenses produced different results, especially when used on different bodies. But I hadn’t heard much about autofocus variation.For those interested, the luminous landscape website recently posted an article about back focus:, I’d love to see the test results of the same lenses over time. It would be an interesting test to find out which lenses are better made and retain sharpness after heavy use.

  • Richard Ford

    And this has what to do with making iconic images?

  • Bakerman

    Thanks for the informative comment !

  • Anonymous

    This is comforting. Especially seeing how the Zeiss glass compared to the lower grade Canon glass….

  • Bob B.

    um…I very recently purchased the Canon 100 L IS f/2.8 macro.  Um..I have a lot of L primes and a Zeiss prime…and I have to say …even with its plastic barrel (@$1000!) it is to my eye…the sharpest lens that I own… I am not surprised to see the plots on the graph in this post!