Nikon finally gets the noise down.

Started Nov 17, 2007 | Discussions thread
ejmartin Veteran Member • Posts: 6,274
Re: Read noise in ADUs greater w/small pixels

John Sheehy wrote:

ejmartin wrote:

John Sheehy wrote:

The FZ50 has 16.5 pixels occupying the same sensor area as a single
5D or 1Dmk2 pixel. All in 12-bit ADUs, the FZ50 has a blackframe
noise of 2.7 ADU, and the 1Dmk2 1.25 ADU, and the 5D 2.0 ADU. 2.7
ADU stacked 16.5 times becomes about 0.66 ADU; a stop better than the
mk2 and 1.6 stops better than the 5D.

Don't 16.5 stackings of 2.7 ADU of noise generate 11 ADU of noise?

Yes, but that would be in 16-bit values, which would be 0.66 ADU in
12-bit, our original frame of reference.

OK, I see the point. I was thinking in terms of electrons -- just a different frame of reference.

But I'm still confused. Is this the ISO 100 read noise of the FZ50? It would seem so since you're quoting DSLR values for that ISO. So there is an advantage at low ISO. For high ISO presumably the CCD FZ50 doesn't do well at all compared to the CMOS DSLR's, with read noise staying about the same in electrons, while the CMOS goes down dramatically. At high ISO it would seem the FZ50 is going to do much worse than the DSLR (though I haven't put in the numbers; running out of re-edit time), since the read noises of the FZ50 and the 1D3 for example are going to be comparable at ISO 1600, but you have to bin 16 of the former to make one of the latter and thus the FZ50 binned is going to have rather worse read noise in aggregate.

To realize this benefit of small pixels at high ISO, don't you have to do it in CMOS, and won't that take up quite a bit larger fraction of sensor space for electronics (16 times in your example) that will cause a bit hit in QE? It doesn't seem that there is a real-world exemplar to examine for that scenario.

One always has to wonder if they've done all the math right with this
stuff, before drawing conclusions, but if you actually do or simulate
this stuff, it is easy to see that the noise at the pixel level,
relative to the signal, divides by the square root of the number of
elements added together.

Some day, I hope to get my hands on something like an FZ50 and a
1Dmk2 or D3 at the same time, and take the same shot with the same
real focal length, and manual exposure parameters, and demonstrate
the difference from that. So far, I've done it with my 10D and FZ50
(biggest pixels I have vs the smallest): - for the text


This is ISO 1600; the benefit for the FZ50 is even better at low ISOs.

Nice demo. I noticed though that the test conditions were f4; that would put the FZ50 at or about the onset of diffraction, but still at the optimum sharpness for the image. Unfortunately the FZ50 won't go beyond f11, but if one is going to scale up the sensor to DSLR dimensions one will for many applications want to stop down to f11-f16 (or more for macro). Do you have a sense for what diffraction is going to do to the clarity of the FZ50 image at smaller apertures? I suppose it would be easy enough to simulate in IRIS by convolving with an Airy PSF, or rather deconvolving the f4 PSF and then convolving with Airy for the smaller aperture (which two steps amounts to a slightly modified PSF in a single step). Or redoing the test at f11 might begin to show what is going to happen.

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