Pixel density - can the playing field be leveled???

Started Jun 6, 2009 | Discussions thread
Malcolm Practice Contributing Member • Posts: 593
Re: some more thoughts

cpw wrote:

So let's go with this a little more. Always interesting to guess what Canon's done, on the subject of lowering sensor read noise from 1DIII levels to 50D levels, I remember we discussed a little in the past:

http://forums.dpreview.com/forums/read.asp?forum=1019&message=32494547&q=impulse+read+noise&qf=m

Elimination of the impulse noise could explain it, but also you bring up the possibility of going to a smaller SF. So, if it is a smaller SF, like in going from 40D to 50D, you could possibly get to a lower read noise. However, if then they retrofit this newer SF design into the 5DMkII, wouldn't this camera also have the lower saturation capacity (as seen by D3)? It doesn't seem to (65,700 e- for 5DMkII, 6.4 micron pixels vs. 65,600 e- for D3, 8.5 micron pixels;

I'd guess that's a good indicator that Canon hasn't fitted a new SF into the 5DII pixel. There's a good chance that the 5DII sensel design is identical to the 1DsIII, at least so far as the silicon is concerned. If Canon had decided to put in the investment to come up with a new sensel design, my guess is they would have chosen some other MP count for the 5DII, either lower, so as to protect the 1DsIII a little better, or higher, to best the A900/A850 and any forthcoming D700x. So, my speculation would be that they have identified th cause of the impulse noise, and eliminated it. It could, however, be possible to shrink the transistor and leave the saturation capacity the same. In a CMOS sensor, the saturation capacity is primarily determined by the voltage swing of that transistor (unlike a CCD) if it's possible to produce a transistor with a bigger voltage swing for the same supply voltage, then the capacity can be preserved. I suspect that a large part of the Canon 'magic' is in the doping and geometry of that transistor - it's one place where their longer history of high quality CMOS sensors gives them an advantage over the competition.

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Mal

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