f-number equivalent between m43 and FF

Started Mar 25, 2014 | Discussions thread
Great Bustard Forum Pro • Posts: 40,760
Still incorrect.

dwalby wrote:

OK, let me reword my statement a bit. A pixel contains an analog signal value prior to A/D conversion. Every analog signal has some sort of noise associated with it, and the A/D conversion itself introduces read noise. So each pixel, when sampled, has a signal level, and some uncertainty due to the noise.

The amount of light falling on the pixel during the exposure is subject to uncertainty, due to the nature of light itself.  This is known as photon noise.  Then the sensor adds additional noise, which is called read noise.

Bob is saying that a single pixel does not have noise, because he is computing the noise by taking the average value of a patch of pixels that should have uniform values and computing the standard deviation.

However, we could compute the noise of a single pixel by instead taking several identical exposures, recording the values of a pixel, computing the mean, and then the standard deviation.

Regardless, it is *crucial* to understand that noise comes from the light itself (photon noise), and that this noise is an inherent property of the light, having nothing, whatsoever, to do with technology.  The sensor and supporting hardware then adds in additional noise (read noise).

Except for the portions of the photo where the light is very low, the photon noise is the dominant source of noise.  Thus, for deep shadows and/or very high ISO photography, the read noise becomes an important factor, but until that point, it is the photon noise that is dominant.

Either way, it is not per-pixel noise that matters, but image noise, and this is a function of the total amount of light falling on the sensor (and sensor efficiency), not the amount of light falling on a single pixel.

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