NEX-6 PDAF problem with 55-210mm?

Discussion in 'Sony Alpha E-Mount Cameras' started by addieleman, Apr 13, 2013.

  1. addieleman

    addieleman Passionate amateur Subscribing Member

    Nov 13, 2012
    Ad Dieleman
    So I rebought the 55-210mm to use on my NEX-6 again, this time a somewhat better sample.

    I updated the firmware of the lens immediately to enable PDAF. And now I get erratic focussing, irrespective of whether I set the "Phase Detection AF Area" to On or Off in the menu. This is only logical as I have learned from another thread that this only makes the PDAF grid visible or not and that PDAF is always active.

    It looks like PDAF looks at a larger area than indicated by the focussing spot (I use flexible spot). In the example below I focussed on our dog's eye and the spot was completely filled with the dog's head. You can see that the photo albums behind are nice and sharp and the dog's head is not.


    Looking for a confirmation of this theory I did another test. First picture was taken at f/6.3, the second one at f/8. Both are focussed with the spot fully located within the lamp, incorporating the brown-to white transition in the bottom to have ample contrast for reliable focussing.
    I also switched Live View Display to On, which effectively takes care that the lens focusses at the aperture set, not its maximum aperture. And because PDAF only works at apertures of f/6.3 and larger (wider opening, smaller f-number), the lens uses PDAF for the first picture en CDAF for the second one.

    The first one at f/6.3. Lamp is not really sharp, optimum sharpness is somewhat behind." >

    The second one at f/8. Lamp is as sharp as it gets.

    It's a bit erratic, I feel like it's unpredictable where PDAF picks the target to focus on. I've done this testing after using the lens for a day or two and getting unexplainable focussing errors. The Sigma 30/2.8 and 19/2.8 behave perfectly as well as the Sony 10-18mm; the latter also uses PDAF but due its large depth-of-fields small errors apparently go unnoticed so I haven't these issues with the 10-18mm.

    Has anyone else discovered anything similar? Any known solutions? I'm pulling my hairs now that I've updated the lens' firmware, according to the Sony support pages there's no going back. I've read a very long thread on dpreview discussing these kind of issues with the 16-50mm on the NEX-6, pointing a bit in the same direction, although there didn't seem to be a conclusive insight. Please don't tell me to stop pixel-peeping or go take pictures or similar comments.
  2. Poki

    Poki TalkEmount Hall of Famer

    Aug 30, 2011
    We're not on dpreview here, so the last line is kinda pointless ...

    To the point: It seems like with PDAF we also get front- and back-focusing issues back in our NEXes. This usually is a problem of a specific lens, not the camera.

    Problem only is: The contrast detection AF that takes action after the PDAF marked the distance should completely avoid such problems, so I can only explain this issue to myself in so far that the PDAF is off by too much to be corrected by the CDAF, which is supposed to only correct in very small margins. Because of this, Sony probably doesn't bother too much with correcting back-focus issues in E-Mount lenses - it simply is not necessary with CDAF systems.

    What can you do? Well, for the moment, trade your lens for another copy that might be better. For the future, Sony hopefully adds better quality control for this issue and maybe even a firmware update that allows the CDAF to correct in bigger margins (which would slow down AF speed, unfortunately).
  3. addieleman

    addieleman Passionate amateur Subscribing Member

    Nov 13, 2012
    Ad Dieleman
    Point taken, sorry. :eek: 

    My exact same feeling: I left the DSLR world mainly because of all this focussing cr*p, backfocus, AF fine tune, all that, and now I get it back :mad: .

    I hope that Sony extends the PDAF setting menu with one extra option: PDAF off. That would simply solve my problem. I'm going to ask Sony support if it's in any way possible to go back to the firmware 1 version for the lens, you never know.

    For now I can think of these workarounds:
    1. Set Live View Display to On and use the lens at f/7.1 or smaller; will give focussing errors if you forget to stay at f/7.1 or smaller.
    2. Trade the NEX-6 for a NEX-7 which doesn't have PDAF. Problem is, I like the 6 a lot!
    3. Trade the lens. Again? Yuck. So far I've had four Sony lenses two of which were real duds, and this one is at least optically decent.
    4. Use (D)MF. Defeats the purpose for which I bought the lens. I can do MF just as well with my Minolta legacy glass, although I won't have OSS then. Trade-off is higher image quality, even with a Minolta zoom lens.

    All else that's left is to wait for Sony to fix it, if and when that happens.
  4. WoodWorks

    WoodWorks Super Moderator Subscribing Member

    Dec 12, 2012
    Ashland, OR, USA
    For what it's worth, Ad, I was one of those who had the PDAF back focus problem with my first SELP1650. I sent it in to the Sony service center in Laredo, Texas, and they promptly replaced it with a new one. Though it was fairly easy to see the problem with my first copy (AF on a high contrast target, click the shutter, and then sharpen focus using DMF, click again), try as I may, I can't get my second one to miss focus. Clearly Sony has some QC problems with their lens design/assembly, but if you like the lens, it's worth trying to get a new one.
  5. Bimjo

    Bimjo Super Moderator Subscribing Member

    Oct 28, 2011
    Washington State
    Ad, I'm curious- you're using flexible spot. Does it do the same thing if you use the center spot and focus/recompose?
  6. addieleman

    addieleman Passionate amateur Subscribing Member

    Nov 13, 2012
    Ad Dieleman
    Thanks, Woodworks, I had just enough time to return the lens to the store. I opted for store credit, I don't have time now to try out other samples until I hit a good one by accident. Buying lenses is like a lottery these days and I haven't been lucky with lotteries so far.

    Bimjo, I didn't try the center spot because it's too large for me. Can't try now, no lens anymore. :) 

    This whole thing drove me mad. I've had 4 Sony lenses now, three of which had a problem and the fourth one, a 10-18mm, is just about acceptable although not perfect. I'm getting quite frustrated with these manufacturers that screw me by delivering junk like it's the most normal thing in the world. I don't think I'll buy another Sony-branded thing with glass in it, at least not in the near future.

    It's not only Sony either. I went through 4 telephoto zooms for my Panasonic ยต4/3 outfit to end up with a Minolta MD 75-150mm as the most decent option. I've been an amateur photographer for more than 35 years now and all this time equipment gave me problems, from my first camera that had the wrong flange distance (!) until now. Can't remember how many times I've had to return stuff. I'm seriously starting to ask myself if I want to spend time in my life to deal with this cr*p, giving up on this hobby starts to become a serious option.

    Had to get this off my chest. Maybe I'll recover. :) 
  7. Bimjo

    Bimjo Super Moderator Subscribing Member

    Oct 28, 2011
    Washington State
    I can certainly understand the frustration. I've gotten much more deliberate in taking photos sine I got my 5N and started using legacy glass. I seldom use AF lenses unless I plan to be out of town and not sure what I'll be shooting, or can't reasonably use a tripod.

    I've been fortunate with my E-mount AF lenses though. With the exception of the 16, I've gotten good copies on the first try. It almost seems that Sony quality has dropped as the NEX bodies get more popular. It's like they can keep up with demand, but not at the previous quality. Sad on several levels.
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