I have since verified that this problem does not occur when shooting in infrared, thus establishing that the problem is a form of chromatic aberration, and an excellent example of how real and theoretical depth of field are often at odds when chromatic aberrations are present. Though the color (visible light) image was shot with the 1Ds Mark II, and the infrared image was shot with the 5D, I think the results can be trusted (besides, I’m not going to convert a 1Ds Mark II to infrared!).
More than likely what’s going on is that by shooting in infrared, a narrower spectral band is used, and thus the color fringing seen in visible light (due to the broad spectral range) simply doesn’t occur. A common misconception is that infrared images are not sharp as sharp as visible light images; this is simply untrue and will be explored in a future article. Both images below are well out of focus at f1.2.
|EF 85mm/1.2L II USM on EOS 1Ds Mark II
f1.2 @ 1/160 sec
65mm behind plane of focus
80% of the way from center to right edge
|EF 85mm/1.2L II USM on Canon 5D
f1.2@ 1/100 sec
80mm behind plane of focus
85% of the way from center to right edge