Quote:
Originally Posted by markas
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.
An wave/particle in an optical train is well charasterised 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
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All good. I've found many of the responses useful. Thanks to one and all for keeping the thread relevant and informative.
Now onto the subject of: life the universe and everything....