1. Reminder: Please use our affiliate links for holiday shopping!

Decentering -- Sony 16-70

Discussion in 'Sony Alpha E-Mount Lenses' started by scott0487, Feb 25, 2015.

  1. scott0487

    scott0487 TalkEmount Regular

    25
    Jan 9, 2015
    I have read a little about potential decentering issues with the Sony 16-70, but I am not sure that I am very good at seeing it in a photo. I understand that it means that the lens elements are slightly off center and that the sharpest area of a photo isn't at the center where it should be. When a lens copy is decentered, how obvious is it in resulting photos, and does the effect of decentering remain constant throughout the zoom range? What are the best ways to quickly test a lens for decentering?

    Thanks very much,
    Scott
     
  2. WoodWorks

    WoodWorks Super Moderator

    Dec 12, 2012
    Ashland, OR, USA
    David
    I used to test for it by taking a shot of some flat surface with a lot of detail (brick wall, etc.) with a camera in an upright position, and then again with the camera upside down. You can then easily compare the sides of the frames to see if there's any difference.

    But I don't really bother any more. I mean, if the flaws of the lens aren't visible in the photos it's used for, why go through a lot of trouble to go looking for them?
     
    • Agree Agree x 2
  3. scott0487

    scott0487 TalkEmount Regular

    25
    Jan 9, 2015
    I agree and am not really a fan of testing other than to see quickly whether it's a big enough issue to have to return the lens within its return period. So, I'm guessing a decentered lens has the same effect across the zoom range? I'll look for samples others have posted. I just wanted to be sure to be able to spot any issue that would be obvious to everyone else when looking at a photo. Thanks.
     
  4. shnitz

    shnitz TalkEmount Regular

    26
    Jun 15, 2014
    I had a Nikon 18-200mm VR on a D80 that was decentered. I noticed it because one day I took a torso-shot of someone, stopped down pretty decently in good light, and when I was editing the photo, the guy's hand was blurry, like it was out of focus. When holding my camera in landscape orientation, the bottom of the lens towards my left hand would just be blurry in certain situations (i.e. at a certain zoom range and focus distance). Didn't always appear.
     
  5. Dan Euritt

    Dan Euritt TalkEmount Regular

    191
    Jan 11, 2014
    i test lenses by shooting equidistant objects, at medium landscape distances, using wider aperture settings... stopping down hides defects.

    with decentering, one side of the frame is usually blurry... you need to test zooms at several points along the focal length.

    another problem to look out for is out-of-focus areas in the frame... instead of one entire side being blurry, it might be one-quarter of the picture that looks like it's out of focus.

    i have a bunch of decentered lens examples on my website, but here is a good tutorial on decentering... check out the example of what happened when nasim dropped a lens, and failed to check it afterwords... he went through the hassle and expense of going to utah to shoot, and ended up with ruined images:
    https://photographylife.com/what-is-a-decentered-lens

    there are a lot of camera owners who wouldn't have a problem with that failed picture.
     
    • Informative Informative x 1
  6. WoodWorks

    WoodWorks Super Moderator

    Dec 12, 2012
    Ashland, OR, USA
    David
    I suppose there are some. But I can't imagine missing that softness on the horizon if it were one of mine. Even at forum-posting size.

    But it's an excellent example of what I meant when I wrote: "...if the flaws of the lens aren't visible in the photos it's used for..."
     
    • Agree Agree x 1
  7. Dan Euritt

    Dan Euritt TalkEmount Regular

    191
    Jan 11, 2014
    that's what i ended up doing... i tried brick walls and imatest charts, and there is a place for that, but if i can't see it with medium landscape infinity test shots, it's probably not a big enough problem to matter.

    the important thing is to look at a lot of different lenses, so that you can recognize the problems, and then use that knowledge to evaluate glass that you want to keep.
     
  8. scott0487

    scott0487 TalkEmount Regular

    25
    Jan 9, 2015
    Thanks everyone -- there is some very helpful information for me here. Thanks also for the link; it provides a good explanation and practical guidance for doing a quick test. Thanks.

    Scott