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Old 28-10-2013, 03:40 PM
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I used to use dark flats and subtract them making the master flat.

I talked to Don Goldman and he said he just subtracts a bias and does not do dark flats.

I then tried that and I noticed better results. My CDK17 and 16803 camera vignette quite a bit so good flats are essential. I got the best results this way.

My procedure (not saying its the best) is about 6 darks into a master (my cameras are very low noise anyway) some are made from more like 15 darks. Its hard to do more than that as 1x1 binned files are 32mb each and CCDstack fails at about 15.

I take 3 flats for each filter and use the default combine in CCDstack.

I have a separate bias. I think I can up the number in it. I think some I use are only 3 biases so I should see if more makes a meaningful improvement or not.

Dark subtraction importance probably varies with camera brands. Some are cleaner than others. We should start a thread posting examples of 10 minute darks to get an idea of which are the cleanest.

My FLI Microline 8300 is the cleanest camera I have used. Amazingly perfect at -40C.

Greg.
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  #22  
Old 28-10-2013, 03:49 PM
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Jay,
the use of flat darks has been around all the time...certainly in the AstroArt manual way back to very early versions.
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  #23  
Old 28-10-2013, 06:09 PM
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Greg you need to expand out the Virtual memory in CCDstack. I stack out over 50 frames easily once I changed the settings. I made my VM setting to 4000mb, but will change this again soon. Having heaps of RAM helps control this. Currently have 16gig on board.

It would also help you to do the calculations in something like CCDAP which tells you how many darks you need for any given set of subs. Using dither helps too, so you will not need as many darks.
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Old 28-10-2013, 06:28 PM
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Darks only compensate for the bias and thermal noise....also handy to suppress the hot pixels....
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Old 28-10-2013, 07:20 PM
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[QUOTE=Paul Haese;1028391]Greg you need to expand out the Virtual memory in CCDstack. I stack out over 50 frames easily once I changed the settings. I made my VM setting to 4000mb, but will change this again soon. Having heaps of RAM helps control this. Currently have 16gig on board.

Good tip. Thanks Paul I'll check that out. Its still quite slow to load and do an action once you do have several images up though. You'll find the 11002 slow compared to your 8300 images which are small. Its just file size and is unavoidable when using these bigger chips.

Are you able to post a 10 minute dark at say -30C?

Greg.
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