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Old 04-05-2008, 11:01 AM
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Stacked dark frames?

I've read in many places that multiple dark frames should be taken during a photography session of DSO's. Some people even take an equal amount of dark frames as they do light frames.

I'm having trouble finding how these multiple dark frames are combined into one master dark frame that can then be used on the individual light frames.

Is that how it's done or should a light frame be shot followed immediately by a dark then that dark subtracted from the light frame that preceded it?

The stacking software that I have, and others I've read about online, allow for the subtraction of one dark frame, not multiple darks.
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Old 04-05-2008, 11:07 AM
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What program are you using to process your light frames Kirkus? The theory is the similar/same for most programs but how you implement it may be slightly different. Eg. DeepSkyStacker you just open all your lights, darks and flats and let the program go to work, ImagesPlus can be automated similarly or you can approach it in a step by step manner.

In the end though the outcome is the same. The darks are combined using an average, median or (rarely) mode combine to produce the Master which is then subtracted from your light frames.
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Old 04-05-2008, 11:43 AM
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Kirkus, Paul is dead right, as always, however if your camera is capable of ICNR, meaning, the camera will take a dark automatically each time you take a light, then there is no need to take individual darks at all.

However your the time taken to take your lights will be doubled whilst the camera is doing this ICNR, but your darks will then be perfectly matched to your lights regarding length and temp.

You then only have to take some flats, combine them and make one master flat, just load them all into your program, and you will end up with one combined image of the entire image run.

Leon
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Old 04-05-2008, 12:34 PM
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Thank you for the replies.

1ponders: I'm Macintosh based, so I doubt many (if any) members here would be familiar with the program(s) I use. I have a wonderful program called AstroIIDC that I use for capturing video and that eventually I'll use for tracking. It's also used for stacking, etc. But it only processes video files. I can use it to create a multiple frame video file from the tiffs off my camera then select 1 dark frame that it then subtracts from all frames in that video.

Actually, I do have a program called Lynkos that I've used in the past for planetary stacking and it does allow for multiple darks and flats to be used during stacking. However, the program is highly processor intensive and hangs up my computer on occasion. I thought if I could manually create a master dark I could then use it with the first program I mentioned, AstroIIDC, which isn't nearly has hard on my computer.

leon: Paul is dead, for sure. I have a Canon XTi (400D). Unfortunately it doesn't have ICNR. At this moment, the extra time involved allowing the camera to perform ICNR would be a welcome change.
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Old 04-05-2008, 12:46 PM
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Can you create a master dark frame the same way you create a multiple frame video of your lights and then use that master to subtract from your lights video?
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Old 04-05-2008, 04:45 PM
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Hi,
The Canon 400d does have ICNR, its in the custom menu function.

cheers, peter
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Old 04-05-2008, 05:11 PM
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The darks need to be median combined or averaged- not just added together.
Acrually ICNR has advantaged and disadvantages. Takes up valuable imaging time is the main disadvantage. Also there is a theoretical advantage to averaging the dark frames to reduce random read noise.
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Old 04-05-2008, 05:48 PM
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Quote:
Originally Posted by Kirkus View Post
leon: Paul is dead, for sure. I have a Canon XTi (400D). Unfortunately it doesn't have ICNR. At this moment, the extra time involved allowing the camera to perform ICNR would be a welcome change.
Hi,

I have a 400D as well; definately it does ICNR and I have used it in this mode. It's available from one of the in camera user functions. Two or three I think.

P.S.

I hope Paul isn't in fact dead

Cheers
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Old 04-05-2008, 07:59 PM
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After being up til the wee hours this morning I'm feeling a bit that way atm
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Old 05-05-2008, 05:28 AM
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Hi. My name is Kirk and I'm an idiot.

I read that part of leon's post as "Paul is dead, right?". I thought it was some reference to Paul McCarney being dead when you play one of their albums backward, and that there was some connection to astrophotography that I was missing. I didn't take the time to realize he was talking about 1ponders nor, apparently, to take the sentence with the punctuation.

And now that I read my explanation, I sound even more like a bloomin' idiot.

I'm just going to try and forget that this happened. Okay.
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Old 05-05-2008, 06:03 AM
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The 400D does, in fact, have ICNR. It's custom function 2 as Zuts said. That was a hard one to find, but I'm glad I did. I'll try that next time I'm out. Since I'm limited to 60sec. or less until I learn drift alignment or get into guiding, the extra exposure time shouldn't be a problem.

I still want to be able to do it manually however. I just like to know these things and want to get good at it.

The program I mentioned above that likes to mess with my computer will run better if it's the first program I use following a restart. I spent several hours last night experimenting with it (in between restarts ) and to my amateur eye seems to do a good job with multiple dark/light frames. It looks like that's the way I'm going to go.

Thank you all so much!

1ponders: Sorry for killing you off like that.
leon: Sorry for ignoring your punctuation.
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