[g__day (Matthew)]

I am just getting back to astro imaging after a long time off - I have two imaging scopes side by side using ZWO cameras (about 13km NW of Sydney centre).

I am using a ZWO 1600MM-c + 7 filter wheel and ZWO EAF into Williams Optics 132mm refractor and a ZWO 071MC-c Pro into a Moonlight focuser into a Williams Optics 115mm refractor.

Last few nights I am doing test runs on NGC 5139 - mostly I shoot 2 min subs for my testing purposes. I control the 71MC-c using APT and the 1600MM-c using SGP - all at 1x1 binning.

From SGP the 1600MM-c colour filters RGB recieved a gain of 240 - don't ask why - I know how to set the gain and offset (to 50) now per imaging event's sub. The shots were all usable though a tad overexposed. The Luminance shots were totally overblown and useless - I will try a gain of 100 or lower next clear night.

On the 115mm scope with the 71MC-c the results were:
1. 180 sec shots with 240 Gain = all shots fine - around 2,200 stars detected by Deep Sky Stacker (DSS)
2. 240 sec shots with 100 Gain = all shots fine - a bit dim, DSS detects 650 - 750 stars
3. 30 sec shots 240 Gain = 50 stars detected by DSS
4. 60 sec shots 240 Gain = 130 stars detected by DSS
5. 120 sec shots Gain 240 = 3,400 stars detected by DSS
6. 300 sec shots Gain 240 = 787 stars detects - image looks way to overblown at the core

So on the 71MC-c / 115mm refractor I would guess 2 min subs at 240 Gain is ideal - going past this longer subs at lower Gain detected far less stars (I guess the core starts to blow out and you loose individual stars). To me the goal with a OSC camera would be I imagine on this target - find the settings that give you the most detected stars and highest score in DSS. I must admit I never thought of using DSS in this way until now - to do a test scoring run to figure out what camera exposure and Gain settings will land you the best subs before you go for a real imaging run for your local night skies - but now I realise this it seems illusive obivious!

For the 1600MM-c I am going to try Luminance shots of 2 - 3 mins between 0 - 140 Gain and see what I get; for the colour filters 240 gain was usable but I will vary it down and bit and see what the results look like according to DSS #stars, FWHM and Score results!

Hope this helps - happy to share data as we are all learning some new things here!