M101 and RGB imaging

[Robp]

Afternoon all,

This is my first attempt at putting together an RGB image and I'm after some advice on imaging M101 (and RGB in general).

So far I have gathered the following data of M101:
Ha 20 x 900 (5 hours total exposure)
RGB 24 x 300 (2 hours each filter at 1x1)

This was collected on a 130pds with an Atik 314L+

With some clear skies forecast for tonight and possibly tomorrow I need to decide what data to add to the above.

1. Would I be best off increasing the amount of RGB data or just start adding Luminance into the mix? I read somewhere that Luminance data can wash out the colour?
2. If I was to add Luminance data to this set, would it be best to match the exposure times of the RGB as a starting point?
3. Does anyone use a light pollution filter with LRGB exposures? I suffer from moderate light pollution and have a skywatcher LPF from when I used to image with my DSLR that I could use.
4. What amount of Ha data should I be aiming for? Is there some guidelines on what ratios to work to on Ha,L and RGB?
5. Is there a point where quantity of data no longer improves an image and its all about the quality instead?

I'm quite patient so don't mind building an image over the course of many nights (in case its relevant to the questions).

Thanks in advance!

Rob

[kalasinman]

"This is my first attempt at putting together an RGB image and I'm after some advice on imaging M101 (and RGB in general)." Love to see what you've done so far.

[Robp]

Hi Kalasinman,

I haven't had time to process the data yet apart from a quick stack and stretch to see what it looks like. I collected the RGB data last night so need to do some flats this evening.

With a clear night forecast tonight the processing will have to wait until its cloudy

 

[Robp]

Thought of another question as well, is it worth pushing the RGB exposure times higher and is there a way of telling if you are exposing to long due to lightpollution?

I used to see an orange gradient and saturation when imaging with my DSLR but don't see that in my individual RGB stacks.

[ollypenrice]

You should certainly shoot some luminance. The whole trick of mono imaging is that L catches (at least) 3x the signal of  a colour filter. Your colour should hold up under 6 hours of luminance. There are ways of applying your L layer iteratively while boosting the colour saturation at each stage but with two hours of colour per channel you might not worry too much about this.

Don't shoot the L in moonlight.

It's impossible to say anything useful about sub lengths in LP without seeing the data - and personally I know zilch about LP anyway, a case of ignorance being bliss!

Bravo for your approach to taking time and all the data you need to do something worthwhile.

Olly

[johnrt]

Yes, time to start collecting some serious amounts of luminance.

[Robp]

Cheers both, just in time to start the nights imaging.

Starting out without the LP filter and attempting the same exposure lengths as the RGB and see where that gets me.

Moon isn't up yet so will see how much I can manage tonight and report back.

Thanks,

Rob

[Robp]

Well it was a lovely night, stayed clear up until I went to sleep.

I managed to take 5 hours 15 minutes of Luminance and a little more Blue as this was the filter I had the least amount of data for. Flats taken this morning.

The moon did encroach a little onto the Luminance run but it was low in the sky and over the other side. I have given the data a quick stretch before I headed to work and there is a slight gradient. I can't be sure if this is from the moon or light pollution. I'll test restricting the Luminance subs to a few hours and see if the gradient is still present when I get home.

Clearoutside is showing a clear night tonight again but the MET forecast shows cloud. I think three clear nights in a row is an impossibility so I'll either be processing the data tonight or gathering some more.

Hopefully I'll have something to show you soon.

[ollypenrice]

The moon tends to rob you of contrast which is hard to sort out. Gradients, however, can be fixed.

Olly