First time posting here, although I've been a lurker for a long time. This is my current setup:
- zwo 1600 mm-c with zwo filters
- zwo 290 mc as guide camerea
- TS Photoline 130mm f/7 Apo
I've tested it once already, everything appears to work as intended and I've managed to get 10x30sec Luminance of m81 and m82 before clouds rolled in.
I'm going to have a proper clear night soon and there's two things were I'm not quite sure yet.
Ideally I'd like to go as deep as possible on m81 and m82 and catch some of the IFN. Am I thinking correctly that the 0 gain preset in the ASCOM driver is ideal for this? My line of thought here is that with a lower gain it will take longer until stars are overexposed, therefore allowing me to expose longer and deeper.
My intention is to use a 3:1:1:1 ratio (i.e. 3 hours Luminance, 1 hour RGB each). Should I use the same exposure times for the subs of RGB as for L, or should I use different ones?
Keep in mind that usage patterns for CMOS aren't the same as for CCD. Most of the recommendations so far in this thread are fine for CCD, but not optimal for most CMOS cameras. Binning simply doesn't apply with CMOS, there is no good reason to use it (at least, not driver or hardware binning.) Stacking smaller numbers, such as 15-20 subs, is not really optimal in any case, CCD or CMOS...it is just the bare bones minimum you can usually get away with and have the outlier rejection algorithms function at minimal capability. It is always recommended for ideal statistical rejection that you stack more subs...the more subs the better in general.
For this camera at f/7, you could probably be using longer than 30 second subs, unless you explicitly want the benefits of short exposures. Especially at gain 0. If you want to use short subs for the resolution benefit, then I would recommend using a higher gain...either 76 (half unity), or 139 (unity). For L, you might want to use 76, and for RGB unity, and use the same exposures for each. You could do 30 seconds at a higher gain and stack plenty of them (with this camera, you definitely want more than 20 subs at gains lower than unity to average out the quantization error...and if you are using short exposures, then getting lots of subs should be very easy...I recommend stacking 80 or more to get the cleanest results. And for an hour of RGB each, at 30 seconds, you need 120 subs, which would be great IMO! For L, you would end up with 360 subs.)
If you are averse to stacking lots of short exposures, then you might want to consider using Gain 0 for L and Gain 76 for RGB. You could 2-3 minute exposures for all channels. You would then be able to stack only 20-30 subs per RGB channel, and 60-90 subs for L. As long as your L subs were very well exposed, thoroughly burying the read noise in background sky shot noise, then that should be fine. I would try to avoid stacking fewer L subs than that, though, as it is not ideal with Gain 0 on this camera. At Gain 76, 20-30 subs is a bit low for RGB, but you can more easily apply extensive NR to the RGB channels without having a large impact on the final results when combined with L in the end.