Quote Originally Posted by asmodai


Wait, would it be 48%?


I just did out some of the math, but it's getting boring. Link me to where it's worked out?


48% comes from 6.4 microns divided by 4.3 microns, but that's not really the right number. There are two issues involved: difference in sensor size and difference in pixel size. Here's the math:


We'll compare 5D2, 1D3, and 7D. First, crop all the sensors to the same angle of view:


5D2 21.1 MP / 1.6^2 = 8.2 MP


1D3 10.1 MP / 1.26^2 = 6.4 MP


7D 18.0 MP / 1.00 = 18.0 MP


Right away you can see that the 7D has a huge advantage in resolution for focal-length limited situations. But for noise comparison, if you look at 100% crops, you may be misled to think it is noisier, so you need to downsample them to the same resolution, such as 6.4 MP:


5D2 8.2 MP crop / 1.13^2 = 6.4 MP


1D3 10.1 MP / 1.00 = 6.4 MP


7D 18.0 MP / 1.68^2 = 6.4 MP


Now you can take a 100% crop from each of the resulting images and compare for noise. You will find that the 5D2 and 7D are exactly the same, while the 1D3 trails more and more at higher ISO.