Microadjustment of Canon 100-400mm IS II

Discussion in 'Canon EOS' started by http://www.photo-net/chrisd, Jun 2, 2017.

  1. When checking this lens at 400mm it appears to be spot on at f/8 but back focusing at f/16.

    Camera is an EOS 7d mk II

    Is there any way of telling the camera this.

    I know you can microadjust on camera for different focal lengths but that's NOT what I'm asking.
     
  2. Focusing, and I assume, MFA adjustments are made wide open unless you're focusing in live view. I'd suspect that what you are seeing would then by default be focus shift.

    I'd contact Canon and see if focus shift is a known issue with this lens.

    JD
     
  3. No way to fix this unless you focus at working aperture in Live View. I seriously doubt that focus shift is a real issue in this lens, so I would stop doing the test and take some worthwhile photos.
     
  4. If it's not an issue how come it is apparent in shots taken at f/16? I first suspected a problem after a safari in Meru last year - I was photographing small birds and almost all of the shots were not quite as sharp as they could be. This was annoying as the AF was focusing right on the eye. I was prepared to accept that some wouldn't be perfect, due to slight movement of the birds and vibration caused by me not having mirror lock up and not having the camera in a tripod, by expected at least 50% would be good. It was nearer 20%. On larger mammals it's not so obvious anyway.

    The test was run to eliminate the possibility of a lens focus problem, and indeed it has convinced me that at f/8 things are fine. However it was obvious that the sharpest point of focus in the photo did not correlate with where the camera thought it was when focusing at f/16. It's not often I use f/16 in wildlife photography anyway, but I was curious to know if there is a way to fix it. I won't lose any sleep over it, and will certainly be out there taking shots whenever I can.
     
  5. On a 7D2 at f16, diffraction would be a concern to me - at f8 it would be nonexistent. I don't have either of these, ideally it should be pretty easy to determine whether the softness is due to misfocus (perhaps (but unlikely) resulting from focus shift), or due to diffraction setting in as your f stop increases (due to aperture decreasing, and the light having to 'bend' more), but the two are cumulative problems. I've got to admit, I would first do an MFA at working distances, then analyze the images and do a test shoot with static subjects at working distances to see if the diffraction is also contributing.
     
  6. Yes, I agree. At 100%, f16 may well show a reduction in quality compared to f8 and that may indeed be what you are noticing. For maximum resolution at the plane of focus, and if you use apertures smaller than say f5.6 or f8 this is to be expected. I would expect f8 to be better than f5.6 only because the lens will perform better stopped down. Below this, diffraction will start to have more and more resolution-robbing effects.
     
  7. I don't think I'm explaining myself too well here. At f/16 the photo IS in sharp focus when I use a target 20m away but the focus is about 2 cm beyond the point where I am focusing. So for instance, if I was focusing on your nose, your eye might be sharply focused but your nose wouldn't be quite in focus.

    I appreciate that there is more diffraction at f/16

    If I did the same test at f/8 and focused on your nose, your nose WILL be in focus as expected and your eyes would be slightly softer as expected.
     
  8. Thanks Robin. Please see my reply to Marcus Ian
     
  9. That doesn't quite make sense to me. The DOF at f16/400mm/20m for your 7D2 is ~1.5m. @f8, the DOF is ~0.75m. The total DOF doubles, so a change of 2cm for 'peak' focus should be utterly in-perceptable. If you can perceive the transitional zone (which you imply you are), then the difference is WAY more than 2cm...for practical purposes, you should expect at least a foot on either side of peak focus to be perfectly sharp at f16.

    In your shoes, I'd send Canon the lens and camera to calibrate the two together, and see if that resolves the problem (of course I would provide them with details on the 'fault')
     

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