D3 sensor efficiency

Started Nov 18, 2007 | Discussions thread
OP ejmartin Veteran Member • Posts: 6,274
Re: So...

PIXmantra wrote:

...What kind of full well (and corresponding ISO) and actual Unity
Gain ISO did you find on the 1D3?

If I may ask, that is?

The only thing I measured was the "gain" at ISO 100, which is about 20.4 electrons per 12-bit ADU. This translates to a tad over 78,000 electrons at raw saturation at ISO 100. I did not impose upon my friend to do any measurements at lower ISO to see the sensor actually saturate and get the full well depth.

Unity gain, to the extent that it is a useful concept (which I doubt), can be inferred from the ISO 100 measurement; since electrons per ADU is inversely proportional to ISO gain, 20 electrons per 12-bit ADU at ISO 100 is one electron per 12-bit ADU at ISO 2000. But oops! The 1D3 is a 14-bit camera! So is unity gain at ISO 400? This is why I think the concept of unity gain is ill-posed. Change the bit depth and it changes, even if there is no extra information in those bits. If the camera were 16-bit tonal depth (but still with the same DR), would you never set the ISO above 125? I think you would probably want to; there are definite image improvements that result for many shooting situations.

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