f-number equivalent between m43 and FF

Started Mar 25, 2014 | Discussions thread
Great Bustard Forum Pro • Posts: 42,508
Re: f-number equivalent between m43 and FF

dwalby wrote:

What I'm saying also is that because the signal that the pixel is measuring is itself random, there is no clear 'expectation' of what it 'should' be. The best the sensor can do is accurately record the pattern of photons presented to it.

OK, I'll agree with that. But, if you know the theoretical per-pixel SNR of a given sensor, that should give you an expectation of the variance from pixel to pixel in a local area with consistent illumination and color, relative to another sensor with a different per-pixel SNR. So with that information you do have an expectation of how two different sensors should render a particular image even before you actually have the chance to observe and measure that difference.

Let's say we knew the value the pixel should read is 100, but it records a 90.  This singular measurement does not tell us the noise.  For example, we could repeat the experiment a hundred times, and if the pixel records a 90 every time, the noise is zero, but it's just consistently lower than what it should be (think of vignetting, for example).

So, we need multiple measurements to compute the noise.  Either measuring the same pixel over multiple exposures or measuring multiple pixels that should all record the same value for a single exposure.

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