Just wanted to drop a line on the DLA. As long as you are not doing macro photography, the difference in DLA is irrelevant. The most common reason to stop down is the higher depth of field (if you're stopping down for longer exposure times consider an ND filter). Suppose you need f/11 on the 50D to get enough DOF. Framing and distance being the same, you will need f/(11*1.6) = f/18 on the 5D to get the same DOF. In both cases, diffraction limits you to effectively about 9 megapixels. if you would use a point and shoot with 1/1.8" sensor (crop factor 4.55), you would need f/4, again being limited to 9 megapixels by diffraction. There are only two theoretical solutions to overcome this physical limit:
  1. Focus bracketing. Shoot several photos with a bigger aperture and several different focal distances and cobine them with appropriate software. Of course only applicable when using a tripod for a non-moving subject.
  2. Make the sensor big enough to get in the domain of macro photography (higher magnification). Then the simple maths above will change a bit in favor of the bigger sensors. Of course, this solution is impractical and doesn't tell much about a difference between 5D and 50D.



So what do we learn from that? The better DLA of the 5D is only an advantage if you are doing macro photography at really high magnifications (say at least above 0.5 to be of pratical relevance). If this isn't be your main interest, don't care about DLA at all.
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