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  1. #1
    Fuzz's Avatar
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    Default Matching darks easily with Dark Library



    My biggest problem in imaging has always been trying to temperature-match my darks to my lights. I kept track of ambient temperature with a regular outdoor weather meter near my scope and try to match them as close as I could. As a result, many of my stacked images would come out looking very noisy. A common result of mismatched darks is noise in in the stacked image in a consistent streaky pattern (often diagonal).

    Most of the newer Canon DSLRs have an internal temperature sensor that you can read using EXIFTools (temp doesn't show up as part of standard EXIF data). However, reading the temperature one by one for hundreds of dark and light frames to match them accurately is not really very efficient.

    Thankfully, Steve (cdnbob) over on Cloudy Nights has come up with a fantastic solution. He has created a little software called Dark Library, using which, I no longer have to worry about matching my darks. The program:
    • Scans your dark library and read the temperatures.
    • For any set of light frames, it can find the match dark frames (you can set how close to the light temps you want to find (exact, +/-1C, +/-2C, and so on).
    • It can then create a filelist for the the lights + matching darks to use in DSS.

    It has made such a difference for me -- now I don't have to worry about how closely I am able to match my darks, because I know for sure. I no longer have to deal with the streaky noise due to mismatched darks. And without that noise, I can now stretch my images more than before. Here's a quick example of my M33 with manually matched darks and DL-matched darks:


    Dark Library works with most of the major Canon DSLRs. For more details, and to download the software, go to the CN thread here: Telescope Reviews: Dark Library V1.2

    The download link for the latest version (v1.5) is about 2/3rds of the way down (look for cdnbob's post). Instructions on how to use it are included in the download package.
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  2. The Following 5 Users Say Thank You to Fuzz For This Useful Post:

    AJin YYC (09-22-2010),alsetalokin (09-22-2010),astroval (04-03-2012),DaltonSkyGazer (09-22-2010),dmbryan (09-21-2010)

  3. #2
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    Fuzz,

    Thanks this is very good information! Was unaware such a program existed, and agree managing dark files can be tedious! Great find.

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  4. #3
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    FileShare Link Error
    The selected files or folders no longer exist. These items may have been deleted or moved by the object owner, since they shared the object to you. Please contact the sender to find out what has happened to these shared items: "CDNDOB""
    .......


    (Interestingly, the Meade Envisage software takes and stores and uses darks sorted by CCD temperature, which the DSI II Pro camera reports to the software in realtime. It complains if you don't have darks at your exposure settings that are within a couple degrees of the current chip temperature, and selects the correct master dark frame to apply to each subexposure. I wasn't sure what kind of difference it could make...until now. Thanks again for your scientific approach, Fuzz...you are opening my eyes to the subtleties of this process.)

    Cheers--
    --Al
    Last edited by alsetalokin; 09-22-2010 at 01:04 PM.

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  5. #4
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    Quote Originally Posted by alsetalokin View Post
    .......
    You are probably clicked on the download link for an older version. The latest version 1.5 is in post #34 on that thread -- it still works (I just tried it).

    Interestingly, the Meade Envisage software takes and stores and uses darks sorted by CCD temperature, which the DSI II Pro camera reports to the software in realtime.
    Yes, I think this is less of an issue with CCD cameras, which are designed for AP and therefore track/report temps.
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    It's nice with Astro CCDs since they're designed to record that information automatically in the FITS header, and most to keep the CCD cool. That sounds like a great program if you have a Canon camera, Fuzz. A good cloudy night project would be to buy a surplus peltier element with the heatsinks attached from a electric cooler at Princess Auto or Harbor Freight and make a small box with rigid foam insulation. You could then spend a few hours while you do other things getting 20+ darks at each level to average into a set of masters with 1 degree step size.
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  7. #6
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    Too bad my camera doesn't work with this. What a great program!
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    Fuzz and All--

    That is a neat program! It makes me wish I had a Canon!

    But, I'm stuck with a Nikon.

    What's wrong with setting/determining the temperature in your beer box and sticking the camera in and letting the wires trail out the seal and taking all the darks you want?

    Would that work?

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    Quote Originally Posted by seal killer View Post
    What's wrong with setting/determining the temperature in your beer box and sticking the camera in and letting the wires trail out the seal and taking all the darks you want?
    That would be pretty close for building a dark library (the only small complicating factor is that the sensor heats up as it's taking the exposures; even though the ambient temperature in the cooler might stay constant, the sensor temperature might rise). Since darks are taken under controlled conditions, you could build a library at exactly controlled temps (e.g. building a delay between each dark frame to let the sensor cool down).

    But then the main issue still remains: how do you know the temps of your light frames? You need to match the temps between your lights and your darks. The problem with the temperature of light frames (assuming you're not using a cooled camera) is that ambient temperature usually falls through the night and the sensor heats up over time (until it stabilizes) -- the two counteract each other through the night. So it becomes somewhat tricky to know exactly what temperatures the lights were taken at.

    Can you get close match without Dark Library? Sure. I used to make a note of the temperature range through the night of my imaging run, and then apply darks with the same range. It worked about 50% of the time and gave me good clean images. The other 50% of the time I had to aggressively process the noise out.

    The advantage with DL is that I can tell exactly what my light temps are and I can decide exactly what temp darks I want to calibrate with.
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  10. #9
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    Fuzz--

    If I had it to do all over again, I would have a Canon. There is no doubt. The support for Canon is almost overwhelming. All you have to do is hit the 'net and it's all about Canon. Literally.

    Canon's superiority has nothing to do with technical quality. It has everything to do with its market dominance among astrophotographers. I have been told by someone that modifies cameras for astrophotography that Nikon's proprietary attitude towards EVERYTHING makes it very difficult to work with those cameras.

    When I start to think about buying a Canon and having it modified, pretty soon I begin to think about just going the CCD route and be done with it! (Is it as "simple" as that?)

    But, in the meantime I have a Nikon. It does not have an internal temperature sensor. The best I can do is exactly like most people do; watch the ambient temperature and take darks in the middle of a session and at the end and maybe even in-between. (I THINK that is what most people do!)

    I have a beer box and sometimes it even has extra space. (If my LEO buddy switches to tea, I will have a LOT of space.) I can see placing the camera in the frig, trailing the wires out the door across the seal, duct taping the door, letting the temperature drop back to the desired level and taking darks at various ISOs until my heart is content.

    Then I would adjust the temperature by 5*F and do it all over again.

    Isn't the humidity in a refrigerator low? If it is, then I don't see how the camera would be harmed and you can always put the beer back in later.

    What do you (and everyone else) think? Is this just a hair-brained idea?

    --Bill
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    Anyone heard or seen any updates to Dark Library ??
    "cdndob" on CN seems to have gone dormant...
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