For those worried about diffraction.......

Started Nov 17, 2009 | Discussions thread
John Sheehy
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Re: I give you up pixelpepper
In reply to Steen Bay, Nov 22, 2009

Steen Bay wrote:

Yes, bigger pixels (on the same sensor-size) have better per-pixel sharpness/contrast than smaller pixels (everything else being equal), and as the very nice graph posted below (by pixelpepper) shows, we won't gain much in resolution going from 6mp to 20mp on a APS-C sensor, if we're shooting at f/22 (caused of the diffraction), which is a very nice/relevant thing to know, if that (for whatever reason) is what we do.

Regardless of the lack of gross difference between the RAWs, the higher-MP will still be sharpenable, limited practically by noise levels (and artifacts such as mazing). The 7D has resolution frequencies with medium and low contrasts which do not exist in the 10D at all.

The 7D at f/22 still samples a bit on the lean side, according to the rules of proper sampling, even if it doesn't have the popularly-desired eye candy. IOW, density isn't quite high enough to properly sample f/22 with a CFA, with the 7D.

Just did a quick test with my 7D and 90mm Tamron at f/22 and 1/160 out my window at a power cable against a blue sky. The red channel had the "proper sampling" transition of about three pixels exclusive from dark to bright, but the blue channel had only 2 pixels exclusive. Now, this includes the effect of blue light bending around a distant edge, and the influence of the AA filters, and without them, the transition would be faster yet. So, for the rules of "proper sampling" in the blue channel, we might be looking at APS-C pixel counts of 40MP or more to "properly" sample the blue channel at f/22; pixels about the size of those in 10MP compacts.

For a grayscale sensor, the 4.3 micron pixels of the 7D should do the trick for proper sampling at f/22.

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John

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