f-number equivalent between m43 and FF

Started Mar 25, 2014 | Discussions thread
D Cox Forum Pro • Posts: 18,298
Re: f-number equivalent between m43 and FF
2

bobn2 wrote:

D Cox wrote:

goshigoo wrote:

Just read the thread about the new 15 f/1.7; I see people saying f/1.4 is f/1.4 regardless of format

I do agree with this statement on the meaning of f-number, but it is confusing since it is the format + f-number which determines the amount of light captured by a picture, which accounts for the final Signal-to-noise ratio of a picture

The final SNR depends (assuming technology of the same generation) on the amount of light falling on each pixel.

This is not remotely right.

The shot noise varies with the square root of the number of photons. So the more photons a pixel (photodetector) captures, the more certain you can be that the output number is correct. The error bar in the measurement becomes absolutely larger but proportionately smaller.

If you take an array of numbers making up a digital image, the uncertainty of each number gives a random variation in the values, which combines with the varying levels that you want to record. This makes the recorded image noisy. (Spatial noise, not temporal as in a sound recording.)

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