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ollypenrice

Tadpoles

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First I had a doddle of a time getting the Ha 2 nights ago. The autoguider was running at around 0.08 pixel average error and the sky was spot on. 3 hours in 8 min subs.

Then last night the sky was superbly clear but the seeing was bouncy early on when I had the scope to myself and the guiding was dodgy but randomly so, so the stars are round for the colour but not tight or small. I've processed them a bit. An hour per channel unbinned.

Cheers,

Olly.

post-15040-133877351764_thumb.jpg

post-15040-133877351771_thumb.jpg

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An excellent pair of images Olly. Well done.

I prefer the colour one, even if the noise might be a tad higher than the Ha. I find it's usually easier to remove noise from mono images than colour, so the slight difference doesn't surprise me.

8)

MD

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Great image Olly I like both images Hope you don't mind I ran the color version through Noise ninja to see how it dealt with the noise here is the result

Regards Les

large.jpg

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Thanks Les. As ever there's a price to be paid in noise vs detail. I don't have Noise Ninja but see that it has its merits. The noise came from the poor seeing, I think. The FWHM values were jumping around when I was trying to focus, which is always a very bad sign. It would be nice to have a mount that needed minimal guider input on nights like that.

Olly.

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Very nice image Olly, a lot of detail in the Ha version!

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Sorry for sidetracking;

I find it's usually easier to remove noise from mono images than colour, so the slight difference doesn't surprise me.

One trick I use from time to time is to do noise reduction on each channel separately. Sometimes each channel needs a little different treatment (especially the red...)

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Stunning Ha Olly.

When the seeing is poor it is the perfect time to do the RGB but bin it. You don't really loose much resolution because that is being limited by the seeing anyway. As far as noise goes that is always going to be limited by the weakest channel so although you have 3 hours of RGB your noise levels are going to be similar to 1 hour of blue data. That's why binning is so good.

I don't know if you tried using a longer guide star exposure. When the seeing is poor I think it is best to go for longer guide exposures (so long as you don't saturate the star) since this averages out the seeing variations and you get a more reliable centroid with less "chasing the seeing".

If you combine that RGB data with the Ha you should end up with a lovely detailed colour image. Here's something worth trying if you have Noel's actions. Duplicate the Ha then use noels Ha colour conversion using the black deep space version of the tool. Add that into the Ha luminence and RGB layers using methods of your choice.

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Thanks, Martin, for so much advice. Greatly appreciated. I have to say that I don't bin colour when aiming to combine it with Ha. I have always found the mismatch in star sizes to be too great.

It has never worked for me when I've tried it, though I do routinely bin colour when doing LRGB.

You find it works, though?

On the night I shot the colour I knew I was in for a problem because the FWHM values during focus were all over the place, jumping from 1.2 to 4.0 or thereabouts. I think it's a gonner on nights like that but I thought I'd give it a go. I can always shoot the colour again or get some other narrowband wavelengths when the moon starts to reappear.

Cheers,

Olly.

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The stars in Ha are always smaller than RGB even unbinnned. The thing with you colour on this occasion with the poor seeing was that the RGB looks like a binned image because of the poor seeing so my thinking was, you would have been better to bin, the stars wouldn't have been any more bloated but you would have had better s/n ratio.

Your situation is different to ours in the UK and I should think you can normally afford the time to be doing unbinned RGB!

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