[Shiraz (Ray)]

Originally Posted by glend

Thanks Ray, always great to see this sort of analysis from you. One question, in your previous sets of ASI1600 charts, as in the Optimum Broadband Sub Length chart (which included max electron count after stack at various Gain settings), your sub time recommendations were slightly different. Not sure I understand why they changed, and I am ignorant of the calculations required. In my experience the original chart times, were pretty good and usually I was able to adjust (for local conditions) to the recommended sub background sky ADU, which I think was 400 at the time. Can I still go by sub background sky ADU? It seemed a simple test that even I could manage.

Hi Glen. this does not take the place of the earlier sub exposure tables, but is an attempt to extend that analysis to provide an estimate of the total exposure time and the dynamic range as well. The original tables are objective and seem pretty reliable, whereas these total time and dynamic range estimates include a subjective assessment and are less reliable. Suggest that you continue using the original sub exposure tables if they are providing useful information.

I tried to ensure that there would not be any clash between earlier data and this - if there is, I may have used slightly different assumptions in this analysis. Apologies, will cross check. However, the results should still be valid. Cheers Ray

Originally Posted by Imme

Looks good Ray, plenty of work put in to that for the benefit of others!

A question for you - when applying these exposure time to the asi1600 OSC do we need to extend times to compensate for the Bayer matrix?
I've heard conflicting views. Your thoughts would be appreciated.

The Bayer filters absorb ~2/3 of the photons before they get to the sensor surface, so the OSC will need about 3x as long to get to the same result.

Originally Posted by billdan

Wouldn't aperture size vary these figures, e.g a 12in F4 will collect light faster than an 8in F4?

Yes, the aperture size makes a difference but it is directly compensated for by an equal and opposite sampling effect. To illustrate, consider the change from an f4 scope of a given aperture to an f4 scope of twice the aperture. The bigger scope aperture will collect 4x as many photons from any part of the sky. However, in the bigger scope also has 2x the focal length, so the area of the sky from which an individual pixel can collect light decreases by a factor of 1/4. If the pixel size remains the same, the only thing that matters in determining the number of photons in a pixel is the f/number (for an extended object).

Cheers Ray