Noise... camera ISO sweet spots?

Started Dec 28, 2012 | Discussions thread
DSPographer
Senior MemberPosts: 2,277
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Re: The D800 is not ISOless
In reply to Great Bustard, Dec 28, 2012

The D800(E) sensor is not ISOless. If it was, then we would see the DXOmark dynamic range plot drop by 1 Ev for each stop increase in ISO. In fact it drops only about 1/2 Ev from 100 to 200 ISO and drops 2.7 Ev instead of 3 Ev from 200 to 1600 ISO. Above 1600 ISO the D800(E) is ISOless. Another way to check for an ISOless sensor is to check the read noise in e- derived from the full SNR data. For the D800E that is the noise n in the following table (m is full well count and g% is PRNU):

NikonD800E

ISO: 100 200 400 800 1600 3200 6400 12800 25600

m = 54924 26293 13414 6722 3483 1776 833 438 237

n = 5.16 3.25 3.27 2.95 2.72 2.78 2.41 2.81 2.83

g% = 0.30 0.37 0.42 0.50 0.51 0.74 0.00 0.49 0.00

Note: Data at 6400 and 25600 ISO is unreliable because of implausible g% value.

We see the read noise starts at 5.16 e- then drops by about 1.9 e- at 200 ISO. Then it drops about another 0.5 e- to about 2.75 e- at 1600 ISO and above.

Compare this to the Canon 1DX table below:

Canon1DX

ISO: 100 200 400 800 1600 3200 6400 12800 25600 51200 102400 204800

m = 90101 46728 23720 11969 6296 3072 1524 738 332 163 104 52

n = 38.51 19.23 9.98 5.28 3.58 2.19 1.89 1.62 1.27 1.70 1.65 1.17

g% = 0.44 0.43 0.52 0.59 0.71 0.83 0.84 0.76 -0.00 -0.00 5.92 8.38

Note: Data above 12800 ISO is unreliable because of implausible g% value.

Here the read noise starts much higher at 38.5 e- at base ISO, then steadily drops to about 1.6 e- at 12800 ISO. So ISO gain does have a much greater effect on read noise for this Canon camera than for the Nikon D800(E).

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