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Old 06-08-2013, 11:26 PM
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graham.hobart (Graham stevens)
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hot pixel advice

Hello, tonight I am imaging with a cooled 60da FS 60 whilst at the same time taking some shots through the RC 8/QSI combo. Both are being guided via PHD on a mini guide scope. So because I have them both going I can't dither in Maxim which is the only thing I can get to dither for some reason. So now have some nice shots with hot pixels. I have Star Tools and PS 5, I also have PI but I have yet to tackle that. Obviously I have Maxim.
The frames are Canon Raws.
What can I do to get rid of the hot pixels besides dithering, I have heard of hot pixel maps but have never used one.
Cheers
Graz
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Old 07-08-2013, 01:00 AM
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Joshua Bunn (Joshua)
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Im sure PI (probably maxim too) would have an algorithm for rejecting hot pixels during stacking. I know ccdstack2 does, dont know about star tools. sorry i cant provide more help.

Josh
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Old 07-08-2013, 05:54 AM
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Use darks, bias and adaptive dark subtraction. CCDstack may do it. Images Plus does it. Maxim probably does as well.

Take a shot of the same exposure details (length, ISO etc) with the lens cap on at night so no light leaks. Ideally take 16 but less would work.
Sigma reject combine these darks to make a master. Subtract a bias master from them during the procedure.

A bias master is same settings except the shortest exposure time. Its a picture of the noise from the electronic readout of the camera.

Take several, sigma reject combine.

Ideally you do the above at the same temperature you image at. Noise varies with temperature. Adaptive darks help overcome that but try to minimise the diffference.

Once you've made your dark master try to standardise your exposure and ISO settings so they are not all different to make the dark work best.

Work out what that is for your camera. A 60Da is probably around ISO1200 max and depending on your light pollution/ tracking accuracy of your mount maybe 5 or 10 minutes. Bad light pollution needs shorter exposure lengths and a light pollution filter.

Also, why can't you dither with them both going? There's only one guide scope and camera. Can't you dither that and it dithers both?

I hope this helps.

Greg.
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Old 07-08-2013, 08:41 AM
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RickS (Rick)
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In PixInsight you can use the CosmeticCorrection process to deal with hot and cold pixels.
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Old 08-08-2013, 07:52 PM
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graham.hobart (Graham stevens)
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hot pixels

Greg, was using different duration of lights for each camera so was worried when one was dithering the other was still exposing etc. Did lots of darks but no bias frames, will di this and flats this weekend. I am sure deep sky stacker automatically subtracts but will check. Cheers
Graham
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Old 11-08-2013, 07:37 AM
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Quote:
Originally Posted by graham.hobart View Post
Greg, was using different duration of lights for each camera so was worried when one was dithering the other was still exposing etc. Did lots of darks but no bias frames, will di this and flats this weekend. I am sure deep sky stacker automatically subtracts but will check. Cheers
Graham

I see. There are a lot of advantages to standardising the length of your subs otherwise you get this huge library of darks etc that becomes hard to maintain.

I usually only use a few different exposure lengths.

Tracking performance of your mount really determines how long you can go. Longer is usually better than shorter except in DSLRs. Narrowband needs longer to get past the noise.

Greg.
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Old 12-08-2013, 08:20 PM
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Quote:
Originally Posted by RickS View Post
In PixInsight you can use the CosmeticCorrection process to deal with hot and cold pixels.
Works well. I use it all the time. CCDStack also has an easy-to-use method of making a hot pixel map that works well.
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