The mirror is just grazing something and getting slowed down enough in its travel to be caught by the shutter in the frame - hence the shadow at what would be the bottom of the frame.
The reason not everyone sees it is the infamous variation in mirror box tolerances/mirror placement between 5D/IIs. Also why not seen with Canon lenses or with FF 1 series. Depending on lens, the problem may only appear as you focus towards infinity and lens mech extends rearward.
You\'ll get the same effect if you mount say a Leica 19 Mod2 that isn\'t shaved enough on a FF 1 series, mirror slows at top of arc as it JUST grazes rear element shroud (remember lens projects upside down) and just gets caught in frame as shutter trips. Mirror will return as if no issue - you won\'t hear the difference in shutter movement.
Try the same lens on a 1 series FF and you\'ll not see the vignetting - tighter manufacturing tolerances. Same goes if you try them on a cropped body.
Shave the mirror (a hair from the looks of it) or thicker adapters and risk giving up infinity. Many adapter makers typically run their product a little skinny to \"guarantee\" infinity focus. On a 5D/II this can cause problems.
Mar 20, 2009 at 10:03 AM
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