D3X vs 5D2 - myth and reality

Started Jan 26, 2009 | Discussions thread
rhlpetrus Forum Pro • Posts: 25,859
full-well capacity Re: Demonstration

I didn't read the whole exchange, but I'm with you that one needs to know full-well capacity as well to actually compute DR, or am I completely off the mark here.

Can't understand how one measures DR by just looking at darker areas and computing noise there.

bobn2 wrote:

I'm not sure how you're inferring the DR from these SNR measurements,
perhaps you could give us the calculation? Usually, the sensor DR is
the ratio of saturation and read noise (or some multiple of it), i.e
the brightest feature the camera can resolve divided by the darkest.
Your measurements includes the photon shot noise in the sample, and
is also pixel referred (if your samples covered the same number of
pixels). Including the shot noise evens out the DR difference since a
big chunk of observed noise is in the photons and common to both.
Doing it per-pixel referenced tilts it a bit in the 5DII's favour,
because you're measuring a larger area of the image.

I suspect, if I've understood correctly, that the difference in your
measurement from others is because what you're calling 'DR' is
something different, namely the extra exposure that the 5DII needs
such that the resultant reduction in shot noise cancels out the
disadvantage in read noise, which unless I'm missing something isn't
the same thing (or maybe it is, need to think about this). In the
end, I can't see how you can calculate DR without knowing saturation.
--
Bob

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Renato.
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(after Ed Murrow)

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