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An interesting topic.
Longer exposures do collect more data.
As sensors do not have perfect QE, and while the rain gauge theory is not bad, it ignores the fact photons, unlike rain, fall at discreet locations, at which, enough photons have to collect to trigger the sensing pixel.
Pixels can also be "triggered" by thermal noise, sky noise, readout noise....well suffice to say there are lots of noise sources.
When using sub exposures, the trick is to make sure you can collect signal faster than noise....in which case you'll be happy. Begging the question how do you do that?
Things that help here are, more signal ( large aperture, longer exposure, quality optics, excellent tracking etc. ), high QE, low noise sensor ( cooling, low noise electronics etc. )
Hope that helps.
Last edited by Peter Ward; 19-10-2012 at 10:12 PM.
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