Leo's Triplet last night

This is last nights image composite of Leo's Triplet. It is shot thru my TOA-150 at F/5.8 (.8 reducer). I started with my FS-78 but after the first sub I realized that it would fit in the FOV of the TOA so I started over. It consists of; Lum= 75min.,1X R,G,B,= 15min each 2X binned. Flats were used but for some reason the blue channel never seems to match the flat or something? It always leaves gradient which messes up the balance. I am taking several 1X flats and meridian combining them and then again the same with 2X, I don't think that I need to take separate flats for each color channel, Do I???? Anyway... any advise would be greatly appreciated. Thanks,
Tom

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Tom Osterholt said:
I am taking several 1X flats and meridian combining them and then again the same with 2X, I don't think that I need to take separate flats for each color channel, Do I???? Anyway... any advise would be greatly appreciated.

Although darks must be taken at the same binning as your subexposures, flats do not. It is okay to take flats unbinned and resize them for your binned exposures. In fact, these flats will work better than a binned flat.
Do you have Ron Wodaski's first book? He covers this topic well.
How are you taking your flats-light box, T-shirt, or sky? You want to get up to about 50% of your full well capacity and take at least a dozen flats to combine into a master flat.
In most cases you will need to take separate flats for each filter. Dust motes will be in different places on the different filters.

dan

Thanks Bill, Dietmar! I'm still having trouble with the color channels due to gradient from some vignetting caused by the reducer. But I have to use the reducer to fit everything into the frame. I am working on flats to try to help correct each channel, we will see! Thanks again, Tom

Hi Tom,

You've captured some very nice details there! The color balance can use some tweaking, but that comes with time and experience. And Photoshop

And flats? Don't get me started on them... well, I'll say that taking flats is probably one of the strangest dark arts of imaging. Taken incorrectly, bad flats can ruin otherwise terrific data.

An instance of this was when I shot my recent M31. I initially shot flats for that using my once-trusted light box. On examining that flat, I discovered a big bright spot in the blue-filtered flat that did not correspond to anything in my blue-filtered light image. Needless to say, using that flat in my blue data corrupted the image horribly. Fortunately, I also experimented with sky flats that session. With the sky flats, there was *no* such artifact!

Not that sky flats are immune to artifacts: I'm working on a new imaging project (I still need to collect more green and blue data before I feel I'm ready to take on processing, if the skies ever clear without the moon!). On playing with some of the luminance data, I found a dust shadow that did not flat out properly. Sigh.... and so it goes....

Eric