I think this is an excellent tutorial to help anyone with their noise minimizing calculations in different settings.

Very interesting indeed. You have to see through the advertisement for SharpCap and fortunately there isn’t much of that

Some mathematical background info:

www.vikdhillon.staff.shef.ac.uk/teaching...y217_det_ccdeqn.html

And Craig Stark's very similar presentation on this topic:

I wanted to check if my noise calculation were correct so adapted my own spreadsheet to match the data presented in the first video.
Results are very similar, the only difference being the wavelength at which SQM is measured: reading the SQM documentation is should be about 500nm but to match the data in the video 300nm is to be used (well these data are not in the video but the video references to tools.sharpcap.co.uk/ ). Anyone have the same difference?

Too bad that the video ended before gain was taken into account. I have many doubts how to treat it.

The 300 nm in the SharpCap tool do not refer to a wavelength, but to the bandwidth of the filter used. It assumes a bandwidth of 300 nm for the luminance filter, it can be increased to a maximum of 350 nm.

I would say that’s about right, because the bandwidth of the spectrum generated by city lighting is probably around 300 nm.

I meant bandwidth, sorry. But the point was that for 'no filter' I would not assume 300nm bandwidth but a greater value as the SQM meter collects light on a wider range as far as i know.

but I was wrong: arxiv.org/pdf/1701.05019.pdf (page 4, figure 4): measured spectrum range is indeed 300nm, theoretical a little more.

Here is another informative (and at times spirited) discussion on the same topic. That one also addresses the effect of gain.

www.cloudynights.com/topic/573886-sub-ex...00-and-maybe-qhy163/

Basically, the settings I have gravitated towards in my extremely light polluted backyard is a gain of 240 on the ASI1600MM Pro and an exposure time of 8 seconds for luminance, 20 s for RGB and 120 s for Ha, O3 and S2 at f8. That keeps the median ADUs in the low 2000s with my dark ADUs around 800. That puts me just a little more than 1200 ADUs above the darks. According to the cloudnights discussion, that is the optimal setting at which saturation of stars (i.e. preservation of their color) is minimized while preserving maximal dynamic range possible under the circumstances.

I had basically empirically come to very similar values before being alerted to the discussion board by a friend in our Astrophotography group. Bottomline: In the city use short exposures and high gain settings, at a dark site use long exposures and low gain settings, because only there can you really get the return on dynamic range that longer exposures and low gain can provide. It is not possible in the city.

fenriques wrote: I meant bandwidth, sorry. But the point was that for 'no filter' I would not assume 300nm bandwidth but a greater value as the SQM meter collects light on a wider range as far as i know.

That is correct, the SQM meter collects photons over a wider range, but the bandwidth at which man-made light radiates is generally more limited to the visible spectrum and falls within the 300 nm range. Anything outside that range would be deep red or glaring blue/UV. Artificial light generally minimizes those parts of the spectrum.

fenriques wrote: Too bad that the video ended before gain was taken into account. I have many doubts how to treat it.

Exactly what I thought at that point! Too bad he did not elaborate on this topic which is poorly understood by myself.

El Corazon wrote: Here is another informative (and at times spirited) discussion on the same topic. That one also addresses the effect of gain.

www.cloudynights.com/topic/573886-sub-ex...00-and-maybe-qhy163/

Thanks, I read the thread (well ,not all 188 posts...), argumentations are solid but the data presented are mainly empirical. There's another useful thread on CN that discuss the theory behind the calculations:
www.cloudynights.com/topic/536809-conver...o-photon-flux/page-2 (#38)

Do you have an excel file with simulations of suggested exposure times to share? I would like to compare to mine