How does the D3 achieve such high ISO?

Started Feb 17, 2008 | Discussions thread
ohyva Veteran Member • Posts: 6,342
Re: 1D3 full well?

Marianne Oelund wrote:

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.

First it's good to remember the full-well capacity in Canon cams are reached at ISO100 while in D3 it's at ISO200. So comparison at ISO200 is apples against oranges. What's then more important, low noise in general or low noise at certain expo-time&aperture settings, depends then on the aimed use of the gear. I persponally prefer speed for sport photos, so the new Nikon would be tempting if I'd not be so committed with my current Canon gear.

Second I'm still sceptic about these well capacity "measurements". No direct measurement method AFIAK (unless you probe into the chip which I think has not been done (and would probably to some extend interfere with the masurement). If done indirectly based on noise figs, then I'd really love to know how all the different noise sources are separated. And how to ensure there is no in-sensor digital domain NR applied - which is reported by Sony to be one of the methods how they have reduced the noise levels in their new CMOS sensor technology.

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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