>>3407008>The fact that a 600mm f/8 and a 300mm f/4 have the same physical aperture size is NOT the reason why the 600/8 on full frame gives you a picture with the same amount of noise as the 300/4 on four thirdsIt is though. See
>>3406984SNR(pixel) = S/N = (Ev * S * T)/N where Ev is illuminance, S is pixel area, T is exposure time and N is read-out and ADC noise that we assume to be the same between sensors built on the same technology.
Ev is proportional to 1/F^2 where F is the F-number, thus Ev = k/F^2 where k is a value derived from the luminosity of the scene that we don't care about.
F = f/D where f is focal length and D is physical aperture diameter.
Thus SNR = (k/(f/D)^2 * S * T)/N
Let's say we go from m43 to FF by making the pixels 4 times bigger, the lens 2 times longer, but we'll leave the physical aperture size D intact:
SNRff = (k/(2*f/D)^2 * (4*S) * T)/N = (k/(4*(f/D)^2) * (4*S) * T)/N = (k/(f/D)^2 / 4 * 4 * S * T)/N = (k/(f/D)^2 * S * T)/N = original SNR.
