A long time ago, in a forum very very close.... Jon and I had a lengthy discussion [8-|] about comparing crop vs. FF sensors using lenses that correct for the crop factor (e.g. APS-C with 50/1.2L vs. FF with 85/1.8). The 'sequel' was a discussion with Rick, complete with example images reprocessed by Daniel, comparing the same lens on the 7D vs. 5DII, with the latter cropped to the APS-C angle of view. But, that didn't answer the question of comparing the two cameras with different lenses for taking the 'same' shot.


To satisfy my curiousity, I set up a simple test scene and shot it from the same distance with the 5DII + EF 135mm f/2<span style="color: #ff0000;"]Land the 7D + EF 85mm f/1.2<span style="color: #ff0000;"]LII (the latter having a FF-equivalence of 136mm f/1.92). One rationale for this is that these two combinations are two ways to achieve the same image (same FoV, DoF, and perspective). In our previous discussion (at which time I had the 7D and 85L, but not the 5DII or 135L), Jon's contention was that the FF body and the less expensive lens was the better choice (e.g. at current prices, 5DII+135L is $3600 while 7D+85L is $3850; the difference is more dramatic when comparing the 5DII+85/1.8 vs. the 7D+50L), and the FF body would deliver better IQ. He was right, and ultimately, that discussion was one reason why I added the 5DII to my kit.


Anyway, back to the comparison. Shots were taken wide open and at 2.5 and 5 stops narrower than the max aperture. The 5DII was shot as ISO 400, the 7D at ISO 200 (should have been ISO 160 on the 7D, actually, for the theoretical 1.3-stop difference to compensate for the effect of sensor size on noise - in practice, the 7D is relatively noisier than the 1.3-stop difference in sensor size predicts). Focus was manual with 10x Live View.


Minimal RAW processing was done in DPP to even out slight variations in color temperature and exposure - a custom WB was set using the dropper on a neutral square of theXrite ColorChecker Passport, andexposure was adjusted slightly so the clipping squares (brightest white on the ColorChecker) were all similarly exposed. Picture Style was set to Neutral, and all other corrections (ALO, peripheral illumination, etc.) were turned off.


The first composite shows the full image. The vignetting is evident wide open, and a bit worse with the 5DII + 135L, as you'd expect on a FF body compared to using an EF lens on a crop body.


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The second composite is 100% crops from the center. No scaling was done, so the field of the crop is slightly larger with the 7D, due to the 14% lower megapixel count of the 7D (it's close enough that I think comparisons are possible without upscaling or downscaling both sets of images to the same final resolution). Sharpness and contrast are better across the board with the 5DII+135L. Both lenses improve a bit with stopping down.


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The final composite is100% crops from the upper left corner, with a SpyderCube there to provide a specular highlight and some text to judge sharpness. Wide open, the 7D+85L suffers from softer corners (even on crop) and really noticeable chromatic aberration, which is still evident even stopped down to f/2.8. The 7D's noise is also evident, even at ISO 200.


[img]/cfs-file.ashx/__key/CommunityServer-Components-UserFiles/00-00-00-35-15/5DIIvs7D-Upper-Left-Composite.jpg[/img]


So what have I learned? I've learned that I'm glad I have a 5DII - the IQ is excellent! I do like the flexibility of having the 5DII for portraits and landscapes, and the 7D for more reach and better AF for wildlife and birds. The 135L delivers better IQ than the 85L (consistent with reviews) - still, the 85L on FF is really an amazing and creative tool.


The other thing I've learned is that I'm tired of the New England run of rainy weather! I'd rather be outside shooting the world than indoors shooting test scenes. To that end, there's a break in the rain right now, and I've got my camera in the car, so I'm heading out to take some pictures. []


--John