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Newbie qu: How do i know if i have a 'good copy' of a lens?

Discussion in 'Native Lenses' started by agnieszka, Jan 4, 2016.

  1. agnieszka

    agnieszka Mu-43 Regular

    May 1, 2015
    Central Coast, NSW Australia
    Hi there,

    So i have seen on some occasions forum members mention that they received a 'bad copy' of a lens (say, Oly 17/1.8), sent it back and had it replaced with a 'good copy' (of the same Oly 17/1.8).

    How would i know if any new lens that i buy is a good or a bad copy? Are there 'test shots' i can do, and what am i looking for? As i begin to build my collection of lenses (and every so often a more expensive one) i'd like to make sure i don't get any 'duds'.

  2. SojiOkita

    SojiOkita Mu-43 All-Pro

    Feb 23, 2014
    I recently read some nice articles on lensrentals.com about this subject.
    These ones for example:
    LensRentals.com - There is No Perfect Lens
    LensRentals.com - Notes on Lens and Camera Variation
    LensRentals.com - "This lens is soft" and other myths

    Not all this is applicable to micro 4/3 (the parts where it comes to body AF / lens tolerances) but I think most of it is, and there are many interesting things discussed in these articles.
    (it's a rental site so they have very large amounts of lenses - and the guy is a test freak)

    Some defects are quite difficult to spot (for example decentring):
    LensRentals.com - Testing for a Decentered Lens: an Old Technique Gets a Makeover
    I recently found that a lens I had and that I used a lot was probably a bit decentered (it's a bit soft in one side)

    What I do is I make some shots from the same point, focused nearly at infinity and some other focused quite near, and compare with other lenses.
    I found that I have big difficulties to assess a lens sharpness on a brick wall or something like this, so I just shoot a normal scene from my window and the book shelves inside my home.

    If the lens is really bad (that happened to me once), I think that it will be sufficient.
    Is the lens is just "at the edges of the tolerances", however, I would not see it... but I don't think it matters.
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  3. mkallstrom

    mkallstrom Mu-43 Regular Subscribing Member

    May 3, 2012
    Stockholm, Sweden
    I had a decentered lens where almost half of the frame was quite soft. It was visible in normal shots wide open and very easy to see when comparing two shots of the same scene where one is taken with the camera up side down (with manual focus and same point in the center of the frame) and I got that lens replaced.
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  4. aphasiac

    aphasiac Mu-43 Regular

    Oct 18, 2015
    I think it's mostly in people's heads.

    Take a few pictures and pixel-peep on your PC. If you're happy with the sharpness, forget about it.
    • Agree Agree x 2
    • Like Like x 1
  5. Klorenzo

    Klorenzo Mu-43 All-Pro

    Mar 10, 2014
    Just to summarize the content of those article: you have good lenses and defective lenses. Defective lenses are really bad and you'll see that easily with simple tests.

    Between good lenses there is a small variation in performance that partially depends on the pairing on your specific camera. As usual you have many average ones, a few best and a few worst. To really look for a best one, or avoid the worst, I think the only option is to go into a shop and test 5 lenses or more, with the same shooting conditions, and pick the best one by comparison.

    To test a lens you simply take a few shots from a good tripod or with a high shutter speed (1/1000) in good light, at different apertures and focal lengths for zooms.
    Then you need to have a general idea of what you can expect from a lens. Look at the images in this thread for example:

    UPDATED: The Great 40ish Landscape Test (10 Lenses in 40MP HR Mode)

    First notice how small the difference is for all these lenses at f5.6 in the center. Then notice how much they differ in the corners. The 45-175 and the 12-32 are not defective lenses are just not on par with PRO lenses and primes.

    Notice that there are a ton of things that contribute to the final sharpness of the picture: steady hands or tripod, perfect/appropriate focus, aperture, focal length, good light, low iso, shutter shock, good post processing, stray light, correct exposure, etc. And finally that usually you'll notice all these differences only looking at a 100% version of the picture with the nose in the screen.

    My advice: don't worry, be happy
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    • Agree Agree x 2
  6. SojiOkita

    SojiOkita Mu-43 All-Pro

    Feb 23, 2014
    And he also says that there's no real point getting the "best" lens, and that there is no real way of saying which one is the best: several people will select two different lenses as the "sharpest one", and the sharpest one is not necessarily the "best" lens.

    That's right;) 
    The idea is to avoid a really defective lens (there are some, not much, but some).

    I would add that a defective lens can be sharp.
    I had a copy of Oly 14-42 Pancake that was very good on all MF tests, but the focus was always missed when in AF mode.
    I finally got an exchange from Olympus repair center, the new lens is worse in terms of sharpness, but the AF works.
    Last edited by a moderator: Jan 4, 2016
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