[markas (Mark)]

I'm buying into this one quite late, but here goes anyway;

Firstly, the "f-ratio myth":
The amount of light entering the telescope is a function of aperture. Hence the number of photons arriving at the sensor plane is basically a function of aperture.

BUT, the concentration of photons hitting a pixel is also a function of focal length.

If you take Steve Moore's own equations for Signal and S/N you can arrive at a relatively simple relationship that pixel S/N ~ (pixel size/f-ratio)*sqrt(sub time) - all other things such as quantum efficiency, optical efficiency etc being equal.


Similarly, the Signal per pixel ~(px/f-ratio)^2 .

These are very useful rules of thumb in estimating exposure times and signal intensity for your system based on images obtained by other systems of known (px/f-ratio).

Secondly, photons and waves.

Very hard to comprehend, but the quantum mechanical reality is that if you interrogate a wave/particle with wave instruments, you'll get wave answers. If you interrogate the same wave/particle with particle instruments, you'll get particle answers.

A wave/particle in an optical train is well characterised by wave behaviour, but the sensor asks particle questions and the particle explanation works.

Confused? We're not Robinson Crusoe - quantum mechanics is plain hard to understand. As the great quantum theorist Richard Feynman said "if you think you understand quantum theory, you don't"

With apologies!
Mark