Need education on RGB stars with Mono

[Muzfox (Murray)]

Hi all, I've just moved to Mono and working on my first decent project. I'm getting some very nice narrowband data and I do want to also look at adding RGB stars to the final result.

I'm using the 2600mm Pro with Antlia pro filters (3nm Narrowband + LRGB). I'm bortle 5 skies.

For the stars would it be best to use 0 gain for the increased full well depth and then work out exposure time based on checking the histogram? What kind of integration time is recommended for star colour? Any other tips would be great. Scope is the Askar 107phq refractor so star shape is very good across the frame.

[Drac0 (Mark)]

For the 2600mm I suggest using 100 gain where the HGC cuts in - you loose about half a stop of DR but reduce read noise by more than half. I'm only new to mono myself, but I'm finding that you don't need a lot of RGB at all, especially if adding good narrowband data. I'm still working on it myself but I've been trialling a 1:3:6 RGB:L:NB ratio - so luminance equal to the total RGB & narrowband at least twice that, using 30min-60min each for RGB. More seasoned users will be able to provide better advice.

Not sure on the total exposure times - I've based mine on a lecture by Dr Robyn Glover of Sharpcap fame, using the scopes focal ratio, local light pollution, read noise & an acceptable level of noise. I haven't worried about the stars themselves yet, focused more on getting DSO right now.

Good luck, I wouldn't mind some more info myself, but I also enjoy learning by trial & error.

Cheers,
Mark

[Muzfox (Murray)]

Originally Posted by Drac0

For the 2600mm I suggest using 100 gain where the HGC cuts in - you loose about half a stop of DR but reduce read noise by more than half. I'm only new to mono myself, but I'm finding that you don't need a lot of RGB at all, especially if adding good narrowband data. I'm still working on it myself but I've been trialling a 1:3:6 RGB:L:NB ratio - so luminance equal to the total RGB & narrowband at least twice that, using 30min-60min each for RGB. More seasoned users will be able to provide better advice.

Not sure on the total exposure times - I've based mine on a lecture by Dr Robyn Glover of Sharpcap fame, using the scopes focal ratio, local light pollution, read noise & an acceptable level of noise. I haven't worried about the stars themselves yet, focused more on getting DSO right now.

Good luck, I wouldn't mind some more info myself, but I also enjoy learning by trial & error.

Cheers,
Mark

Okay awesome info thank you, that gives me a starting point. I'll hit narrowband again tonight I think and then give the LRGB a go tomorrow night. Moons coming in so don't want to leave it too late lol. I should be ~ 4 hours per HSO at the moment, another 3 tonight will help a lot.

[The_bluester (Paul)]

I have a 2600MM (And an MC as well)

What I have been doing with the mono is, for pure RGB images I shoot at gain 0 to get the best full well capacity, setting the exposure time the same for all RGB subs and setting it to have only a small number of saturated pixels (up to a couple of thousand, remembering that the sensor is 15 megapixels so still a really small percentage) Luminance will typically be shorter and I aim for a similar number of saturated pixels. As well as the number of saturated pixels I pay attention to the lowest values to make sure no pixels will calibrate out to black after a master dark and flat is applied. If they look like they might, I accept more saturated pixels to ensure no zero values.


For RGB-NB images where the RGB is typically just for star colours I shoot everything on gain 100 and use the same sort of values to work out the exposure times. IMO for pure LRGB, low gain produces a marginally nicer image.