How does the D3 achieve such high ISO?

Started Feb 17, 2008 | Discussions thread
Marianne Oelund Veteran Member • Posts: 7,788
Re: 1D3 full well?

ejmartin wrote:

Marianne, where are you getting your figure of 22K electrons at
saturation for the 1D3 at ISO 200? Mine has 71K electrons at
saturation for ISO 100 and about 38K at ISO 200. 22K seems awfully
low, more like the value for the 1D2.

Can you reconcile your values to Roger Clark's 12-bit unity gain ISO value of 1000 for the Mk III? That would imply 20,500 electrons full-scale at ISO 200.

As for the change in Clark's data, he had measured the gain at ISO
50, not realizing that ISO 50 is really ISO 100 overexposed by a
stop. So values for gain above ISO 50 are double what he intially
reported, and read noise in electrons consequently also doubled for
all ISO's above 50. (There was clearly a problem, since if you took
the original figures seriously, the 1D3 had the worst photon
collection efficiency of any Canon DSLR since before the 10D).

Thanks for the explanation - I was wondering. Has this also caused an error in his unity-gain ISO calculation?

If the Mk III unity-gain ISO is actually closer to 2000, then the D3 and Mk III would be back to rough parity regarding read noise, with the D3 retaining an advantage in shot noise.

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