Strange light pattern with telephoto lenses — A7

Discussion in 'Adapted Lenses' started by WoodWorks, Feb 1, 2014.

  1. WoodWorks

    WoodWorks Super Moderator

    Dec 12, 2012
    Ashland, OR, USA
    David
    I've recently acquired a couple of telephoto lenses, a Canon FD 100-300 f/5.6L and a Nikon 180 f/2.8 AIS, and both of them exhibit a strange pattern on the images, especially when stopped down. I've seen this on both the Canon and two copies of the Nikon, so it's not just an adapter issue, or a single lens issue. And I have no filters on the lenses, BTW.

    Here's what it looks like, a shot of the clear sky with the Nikon at f/22, with the contrast boosted in Lightroom to exacerbate the condition.

    [​IMG]

    Has anyone seen anything like this, or have some idea what might be the cause?
     
  2. Bimjo

    Bimjo Super Moderator

    Oct 28, 2011
    Washington State
    Jim
    Is there a baffle in either lens? That's the only thing I can think of that might cause that. Almost like the light is bouncing off the back element onto the sensor, but the baffle blocks part of the reflection or something.

    That's my one guess. What do I win if I'm right? :p
     
  3. quezra

    quezra TalkEmount Top Veteran

    916
    Aug 22, 2012
    Given the shape it actually looks a bit like a wrong-sized hood?
     
  4. WoodWorks

    WoodWorks Super Moderator

    Dec 12, 2012
    Ashland, OR, USA
    David
    No, I just checked, and neither lens has a baffle, and both have the OEM hoods. In fact the Nikon's hood is permanently attached. And the weird effect happens with or without a hood attached and/or extended. Is a puzzlement.

    The Canon doesn't really show the effect until you get past f/11 or so. But on the Nikon you begin to see it at any aperture past wide open.

    If any of you with A7s have a long lens you can try, I'd be curious to see if any other lenses exhibit this effect. I never noticed it until I started using my long telephotos, stopped down.
     
  5. Deadbear77

    Deadbear77 TalkEmount Hall of Famer

    Sep 14, 2012
    Northeast Ohio
    Kevin
    I'll try when I get home from work
     
  6. WoodWorks

    WoodWorks Super Moderator

    Dec 12, 2012
    Ashland, OR, USA
    David
    Here's the effect visible in a shot from the Canon 100-300. It's less noticeable than with the Nikon 180, but still fairly obvious, once you look for it. I think this was stopped down to f/11.

    [​IMG]

    It's not exactly a vignette either, since it occurs well in from the edge of the frame. It's almost like two lighter areas, shaped like brackets.
     
  7. f/otographer

    f/otographer TalkEmount Regular

    196
    Aug 20, 2013
    I would try shooting the sky with any other lenses you have, wide and normal as well. If it is happening on two different lenses and different adapters it looks like it might be a camera/sensor issue. If so it might show up to a lesser or greater degree with any lens.
     
  8. WoodWorks

    WoodWorks Super Moderator

    Dec 12, 2012
    Ashland, OR, USA
    David
    I did the same test with all of my other lenses, both legacy and Sony E-mount, this morning after I saw it with my Nikon 180mm images. None of them appear to exhibit the problem. It seems isolated to longer focal lengths.
     
  9. michelb

    michelb TalkEmount Regular

    197
    Oct 27, 2013
    Greater Montreal area in Quebec, Canada
    Michel Brien
    Page 259 of the A7/A7r guide

    e-Front Curtain Shut. (ILCE-7)
    The electronic front curtain shutter function shortens the time lag between shutter releases.
    1. MENU → (Custom Settings) → [e-Front Curtain Shut.] → desired setting.
    Menu item details
    On (default setting):
    Uses the electronic front curtain shutter function.
    Off :
    Does not use the electronic front curtain shutter function.
    When you shoot at high shutter speeds with a large diameter lens attached, the ghosting of a blurred area may occur, depending on the subject or shooting conditions. In such cases, set this function to [Off].
    When a lens made by another manufacturer (including a Minolta/Konica-Minolta lens) is used, set this item to [Off]. If you set this function to [On], the correct exposure will not be set or the image brightness will be uneven

    Can you try ?
    I only have A7r which does not have this EFCS
     
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  10. addieleman

    addieleman Passionate amateur

    Nov 13, 2012
    Netherlands
    Ad Dieleman
    It's good that we have someone among us who actually reads a manual! Thanks Michel.

    I tried to reproduce what David (Woodworks) is showing here but couldn't reproduce that peculiar pattern. I tested with the Minoltas MD Rokkor 200/4, MD Rokkor 200/2.8, MC Rokkor 300/4.5, MD 300/4.5 and Sigma 400/5.6. I noticed uneven brightness with electronic front curtain shutter on, shown here for the Sigma 400/5.6. Other telephoto lenses showed a similar behaviour. Left is electronic front curtain on; the upper part of the left picture is darker than the lower part. The effect has been exaggerated by applying tone curve correction.

    i-Zz95Qp8.
     
    • Like Like x 1
  11. WoodWorks

    WoodWorks Super Moderator

    Dec 12, 2012
    Ashland, OR, USA
    David
    I tried a fix suggested on a post from the Fred Miranda site, and though it did significantly improve the situation, it didn't entirely eliminate the problem. It did, however, confirm that the problem is caused by light bouncing around the interior of my adapter, and has nothing to do with the electronic first curtain shutter.

    I fashioned a baffle for the adapter, basing it on the baffle of my SEL35F28Z.

    [​IMG]
    [​IMG]
    [​IMG]

    The baffle was a trial and error affair, and I went through six different iterations before I got one that masked as much light as possible without causing any vignetting. But the best version I could come up with still left some of the light pattern:

    [​IMG]

    It's much better than before, and chances are no one but me would ever notice the flaws in the images. But I'd notice them. So in a last ditch effort to keep using these lenses with my A7, I've ordered a Metabones adapter for my Nikon 180mm, which I hope might perform better than the cheap ebay special I'm using now.

    But I'm not holding my breath. I fear there's something inherent in the A7 sensor box design that makes using long legacy telephotos problematic.

    I'll provide more info once the new adapter arrives.
     
    • Like Like x 2
  12. WoodWorks

    WoodWorks Super Moderator

    Dec 12, 2012
    Ashland, OR, USA
    David
    I wonder if the shorter flange distance on the Minoltas vs. my Canon & Nikon lenses may make enough difference to eliminate the problem. But thanks for testing your lenses, Ad.
     
  13. addieleman

    addieleman Passionate amateur

    Nov 13, 2012
    Netherlands
    Ad Dieleman
    I used a Novoflex adapter for all the tests, it has a small rim inside to act as a rudimentary baffle IIRC.
     
    • Like Like x 1
  14. dbmiller

    dbmiller TalkEmount Top Veteran

    777
    Mar 2, 2012
    New England
  15. WoodWorks

    WoodWorks Super Moderator

    Dec 12, 2012
    Ashland, OR, USA
    David
    I don't think so. I can hand hold the Nikon, so there's little to no stress at the lens/camera interface. And the Canon has a tripod adapter. Besides, the pattern is symmetrical. Light would have to leak around the entire perimeter on two different kinds of adapters. Seems highly unlikely to me.
     
  16. WoodWorks

    WoodWorks Super Moderator

    Dec 12, 2012
    Ashland, OR, USA
    David
    Ad, when you did your tests with your long lenses, was it a bright, sunny day, and did you shoot them with closed down apertures? I find the problem is much more obvious in bright light, and only becomes very obvious up above f/11 or higher.
     
  17. addieleman

    addieleman Passionate amateur

    Nov 13, 2012
    Netherlands
    Ad Dieleman
    I did. It was a bright day and I shot with apertures from wide open up to the smallest aperture (f/22 or f/32) and I used 1/1000 s shutter speed. None of the pictures showed something peculiar except for the unevenness shown earlier.
     
    • Like Like x 1
  18. WoodWorks

    WoodWorks Super Moderator

    Dec 12, 2012
    Ashland, OR, USA
    David
    Excellent! At least there's some hope for legacy telephotos on an A7, albeit not much hope for the telephotos that I currently own. :roll eyes:

    Thanks so much for taking the time, Ad!
     
  19. WoodWorks

    WoodWorks Super Moderator

    Dec 12, 2012
    Ashland, OR, USA
    David
    Problem Solved!

    I ordered a Metabones NEX-Nikon F adapter from B&H, which arrived last night. And though I won't be able to test it in bright sunshine for the next few days (we're finally getting some rain out here in SF), I did test it against a bright light and this morning against a grey sky. No matter which aperture I dialed in, I could not detect the strange light pattern when I checked the images in Lightroom. I can't say that the problem is 100% cured until I can test it again in bright sunshine, but I'm fairly certain that the problem was caused by internal reflections in my older, cheap ebay (Fotasy) adapter. The Metabones has a flat black interior with multiple ridges to keep reflections to an absolute minimum. Yeah, it's much more expensive. But at least I have use of this great lens again. Money well spent, as far as I'm concerned.

    [​IMG]
     
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  20. addieleman

    addieleman Passionate amateur

    Nov 13, 2012
    Netherlands
    Ad Dieleman
    Great, that's good to know! Crisis averted... :biggrin: