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 Post subject: M31 noisy image
PostPosted: Tue Nov 25, 2014 3:24 pm 
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Thanks for the comments Andy. I'm not sure what the black spots and the use of the calibration frames is. A bit of guidance at the next meet will be appreciated. The image is far too noisy. The TIFF is the same. I guess that's where IRIS scores over DSS in our polluted skies but I'm struggling to get a decent result in IRIS.
I did 16 10 minute frames but found PHD, after tracking pretty well for a couple of frames, then through a wobbly and was all over the place. I can't blame flexure now as Brian did an excellent job of locking the guider to the scope. Bill C


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 Post subject: Re: M31 noisy image
PostPosted: Tue Nov 25, 2014 3:47 pm 
Good effort Bill, nice image, I wouldn't say it was a noisy image but now the hard bit which is different for every image and every setup and indeed every eye..... The processing....it is very much an individual thing. the black spots are marks/dust on either your scope or your camera sensor...... This is why we take flat/bias/dark frames and why they are so important as they get taken away from the data in the image to get rid of the stuff you don't want in there, light pollution, dust spots etc etc
But your definitely on the rite track....


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 Post subject: Re: M31 noisy image
PostPosted: Thu Nov 27, 2014 10:07 am 
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Bill,
Firstly well done.

For your guiding issues I would always recommend watching the error graph (all night!). This will show whether you are over correcting (big zigzags) or under-correcting (errors take ages to return to zero). Aggressiveness is the setting you have to adjust accordingly. A slight imbalance in the mount also can help - drive working "uphill".

I guess the spots Andy referred to are dust shadows. These are inevitable and flats cannot always correct for them as dust can change from when the flats were taken to when the images were shot. I have seen dust shadows move across the image during a sequence - the DSLR mirror going up and down can move them.

As regards noise, it looks like you have been a bit aggressive on sharpening. This is most evident in the stars overlying the galaxy - they have dark halos. Sharpening always increases noise. Space Noise Reduction from Astro Tools is probably more beneficial than sharpening.

For colour balance - very difficult for us using light pollution filters - I have found Rogelio's White Balance filter (+ HLVG) for Photoshop can overcome some of our problems - see http://www.deepskycolors.com/ It does leave the image a bit darker so you have up the curves a touch afterwards. The HLVG one gets rid of any resulting green cast.


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 Post subject: Re: PHD Guiding
PostPosted: Thu Nov 27, 2014 1:35 pm 
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DRatledge wrote:
For your guiding issues I would always recommend watching the error graph (all night!). This will show whether you are over-correcting (big zigzags) or under-correcting (errors take ages to return to zero).

If you enable the "Logging" option in PHD Guiding, it will save a file containing all the measured errors and the correction-signals sent to your mount over the whole session. On my old WinXP laptop, these files are auto-saved in the My Documents folder.
This text-file (e.g. PHD_log_23Nov14.txt) contains Comma-Separated Values, so you can import it into a spreadsheet program and then plot the required graph for the complete session for analysis and debugging at a later date.


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 Post subject: Re: M31 noisy image
PostPosted: Thu Nov 27, 2014 4:13 pm 
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Looking at your image on my big screen I am not so sure you have over-sharpened it - apologies for that. It looks like general noise but the Deep Sky Noise reduction action in Astronomy Tools will certainly help. Try it twice - once all over and secondly on just the sky area and the very edges of the galaxy. Blend the noise reduced image with the original to taste.

If you use PHD2 Guiding you can watch the guiding graph live. Life doesn't get more exciting than this!


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 Post subject: Re: M31 noisy image
PostPosted: Thu Nov 27, 2014 9:02 pm 
It is a noisy image Bill, but you're confusing noise with rain - the by-product of flexure - something i can talk on as an expert as almost all of my images looked peed on at some stage. Dave has covered this in previous posts, sufficed for us mere mortals - all you need to do is carry on as you are. Work on eliminating whats causing it - could be all sorts- something thats worked loose, could be the camera adapter, the guide cam rotating, a cable snagging somewhere - it could be caused by anything. But the important thing is to keep practicing & refining.
There'll be no end of times you'll waste perfect imaging evenings because of something stupid you've not done or checked.
I do monitor my guiding graph - its a brilliant indicator, but its not the definitive solution for you at this stage - so worry about it - just not in front of everything else. Make sure everything is tight & crack on putting some photons down the barrel. Whackery isn't just related to mounts & its the enemy!!!


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