Steve Spencer
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 p.3 #19 · Image Quality: 7D vs 5D original ? | |
alundeb wrote:
When you compare that way, at pixel level for hi/lo res cameras, and same ISO setting for large/small sensors, you get those results, no doubt.
For normalized pixel count, the 7D leads the 40D by a mile again.
For ~equivalent~ images (Same perspective, FOV, DoF and shutter speed), both 500D and 7D give me better print quality than the 5D at 16x24". Not by a mile, but a baby step for the 500D and two small steps for the 7D.
For time and time again, I see comparisons between different sensor sizes at the same ISO setting. That is biased because even if the framing is the same (that is good, for once), the DoF is narrower or the shutter speed is slower for the full frame sensor. For a comparison of apples to apples, adjust FL * 1.6, f-stop* 1.6 and ISO * 2.5.
Like if you show me an image taken with the 5D, at 135 mm, f/8, ISO400, and say it is better than the 7D image taken with an 85 mm at f/8, ISO 400. I will then answer that those images are different, and I can replicate how the 5D image looks by changing the settings on the 7D to f/5 ISO 160.
The IQ of the 5D shines at lowest ISO, or narrowest DoF, or with wide angle lenses. Those are the cases where the ~equivalent~ on a crop camera is impossible to acheive.
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Interesting method of comparison (by the way I think you mean FL times 1.6, f-stop divided by 1.6, and ISO divided by 2.5), but I think a couple of things follow from this analysis, or are an extension of your last sentence. Any time you shoot at f/2 or faster on a FF the results can't be equalized with a crop camera--even shooting an f/1.2 lens at f/1.2 won't quite get you there. Second, any time you shoot at ISO 200 or 100 on a FF the results can't be equalized on a crop camera. Third, any time you shoot at 15mm or wider on a FF the results can't be equalized on a crop camera as 10mm is pretty much the widest that is available for a crop camera. Of these limitations it seems that the first on--the DOF difference--poses by far the greatest limitations. Even if you shoot at f/2.8 on a FF there are not many lenses that have good performance at f/1.6 and almost all of them are quite expensive and all of them fit in a fairly narrow range of focal lengths (i.e., 24-85mm). This means that in practice it will be quite hard for a crop camera to ever equalize the performance of a FF at f/2.8 or narrower. For many shooters this will occur fairly often if not for the majority of their shooting. For others who always shoot at low ISOs that will be an issue too. What is interesting is that the FL difference which seems more obvious is likely to have a relatively smaller impact. There are only a small number of pretty specialized lenses that are wide enough to not have equivalents on the crop camera.
Thanks for the analysis.
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Or better yet, just use a film camera and lose yourself looking at slides on a light table! Ok, I'm ridiculous, I know. I love my EOS 1-N 
