Saturday, July 16, 2011

Strange 1D Mark III Phenomena with Manual Focus Lenses

I have never encountered this before, with any camera -- when I use manual focus lenses on the 1D III, focus shifts!  I even installed the EC-L cross-split screen on it, and the lines all lined up perfectly which should indicate correct focus.  But, it does not.  It back-focused.  Tried this with a few different lenses so it's not the lenses.

The strange thing is that it's not constant.  Sometimes better, sometimes worse.  And, my auto focus lenses all work more or less perfectly!

If you have encountered this problem, and know why it's happening, I would appreciate hearing from  you.  I am not really upset, since I won't be using manual focus lenses much on the 1D III, but I am a bit disappointed.

Red on Red -- NEX-5 & Rollei QBM 50mm f1.8. Click for larger.


  1. It's most likely an incorrectly shimmed focus screen. Simply put the viewfinder focus is slightly off from the sensor focus. The amount should shift with differing lenses as focal length and depth of focus vary (the later is the sensor side equivalent of depth of field and it changes with different lens designs).

    This is unusual on a 1 Series body as Canon calibrates this at the factory. 5D's are notorious for the problem though.

  2. @Adam: Thanks for the information. I also suspected it was the mirror, but it doesn't seem to affect auto focus. With auto focus lenses, when focus is achieved, the split lines do line up correctly. Very odd indeed.

  3. I agree about the focus screen being the issue. This is not part of the AF chain either IIRC. I used to tune that on film cameras (where one has access to the film plan + ground glass + a hand held microscope)

    I recommend using a good quality manual focus lens which you can tape down and determine how much its out. Then you know which way to shift the focus screen.

  4. As I understand it the AF system is symetrical from the viewfinder using the partially silvered region of the reflex mirror. Therefore its not surprising that you can have perfect AF performance while the focusing screen is slightly off. As other people mentioned it really seems to be a matter of shimming the screen until it is perfect.

  5. Thanks to everyone. Looks like the it's a mirror issue. I am disappointed this happens on a 1-series camera. All of my previous cameras, 1D, 1Ds, 1D II, 1D IIn were perfect and dead on with the split screen. This kinda re-enforces my feeling that Canon's quality control is going down hills.

  6. Any recommendations for Canon M and Samsung NX1000 mirrorless cameras. I have a 200mm and 50mm Rollei lenses. a Pentax 35-80mm and a Canon 75-200mm old zoom lens. Any issues with focusing to infinity?