amp glow

Questions and answers about processing in StarTools and how to accomplish certain tasks.
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alacant
Posts: 146
Joined: Mon Jan 25, 2016 7:03 am

amp glow

Post by alacant »

I think this is what I have. In wipe, it says I need a mask. How do I tag all those red pixels and remove them?
I've put the tiff (at the same stage): https://drive.google.com/file/d/0B_uUt0 ... sp=sharing
ngc1502-1feb.jpg
ngc1502-1feb.jpg (240.72 KiB) Viewed 3302 times
TIA
LanFeusT
Posts: 42
Joined: Mon Jan 19, 2015 6:29 am

Re: amp glow

Post by LanFeusT »

It looks to me like you have a lot of artifacts on the edges. What was your process to get there?

You probably want to be doing an AutoDev first, then crop out the artifacts out (those red borders all around) and follow that with the wipe.
alacant
Posts: 146
Joined: Mon Jan 25, 2016 7:03 am

Re: amp glow

Post by alacant »

Hi
dss of 4 lights, +dark, flat and bias frames.
In st it was autodev then wipe with vignetting and amp glow
I can then work through the modules and get close to a black background but the red pixels are impossible.
ChrisLX200
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Joined: Tue Apr 22, 2014 10:25 am
Location: Macclesfield, UK
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Re: amp glow

Post by ChrisLX200 »

I don't see any evidence of amp glow just a general red bias which is commonly caused by light pollution. With a DSLR you need many more than 4 subs (start with 20), and you should also use dithering between subs (which means to move the FOV a few pixels each time in a random pattern) to even out the background noise. Although dithering won't reduce the red bias (colour blotching) it will smooth it out making it much easier to correct later.

ChrisH
alacant
Posts: 146
Joined: Mon Jan 25, 2016 7:03 am

Re: amp glow

Post by alacant »

Hi
OK. Thanks. Just to be sure:
subs: Is this 20 of everything or 5 of each. Or something else? What does 'subs' mean?
FOV: randomly hit the ra and dec nsew keys on the handset before each light frame?

Sorry if this is all rather basic, but I really appreciate your time.
ChrisLX200
Posts: 90
Joined: Tue Apr 22, 2014 10:25 am
Location: Macclesfield, UK
Contact:

Re: amp glow

Post by ChrisLX200 »

alacant wrote:Hi
OK. Thanks. Just to be sure:
subs: Is this 20 of everything or 5 of each. Or something else? What does 'subs' mean?
FOV: randomly hit the ra and dec nsew keys on the handset before each light frame?

Sorry if this is all rather basic, but I really appreciate your time.
'Subs' = Sub-Exposures which when all added together (stacked) create the final image.

'Dithering' is moving the scope slightly (a dozen pixels or so for a DSLR) in a random pattern after each sub. This is usually done automatically by the autoguider software (PHD2 for e.g.,) if you enable that option.

For lights then take as many as you can, if the subs are (for e.g.,) 30sec each then yes - 20 is a good starting point. The more you have the better signal-to-noise ratio (S/N) you will get when they are all stacked together. This in turn will smooth out the background enabling faint details to be revealed when the image is stretched later during post-processing.

For Bias you want at least 50 - they are quick to take and the 'master bias frame' that is created from them can be re-used for all your images.

For Darks (if you use them) then again, you want as many as you can - say 25 - 50. The problem here is that the DSLR is not temperature controlled and the noise is temperature dependant. My advice would be to not use them for now, and when you're happy with everything else then you're in a position to compare results with/without darks. You may find you get better results without them.

For flats again - you want at least 20 and preferably more, but if you are dismounting your camera and the telescope each time you use them then the flats become invalid for the next time so need be re-taken. That could be a problem! You see the master flat has to accurately represent all the changes in light intensity (vignetting, dust donuts, and so on) which can change each time you setup. The flats also need to be taken with the focuser in the same position that it is set at when taking the lights.

So that's a lot of stuff to get your head around, and some of it may not even apply if you are not autoguiding (like dithering for example). For starters just make sure to collect enough subs (also called the 'Lights' or 'Light Frames'), and enough flats and bias to create decent quality callibration master files (master bias, master flat - DSS will do that automatically for you when you run it). Forget the darks for now.

ChrisH
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