Flintstone Stargazing

January 31, 2009

M42-The Great Orion Nebula on 1/30/09

What a difference flat frames can make! Tonight I finally figured out how to take good flat frames that work with my images. This Orion Nebula image is maybe the best I’ve ever done and it’s only 7 minutes worth of data. The key difference is the flat frames let me get a lot more data out of the image. Well that’s all for now – I need to get to bed.



  1. Very nice image Ed. So what’s your technique to taking flats? Until now I thought they were more trouble than they’re worth.

    Comment by PierreS — January 31, 2009 @ 8:13 pm

  2. More specifically, I’d be very curious how you set your exposure settings for your D50 and how you figured out which flats were valid flats.

    Comment by Pierre — January 31, 2009 @ 8:16 pm

  3. Okay – here’s what I did: (I came across this recommendation on the Maxim DL site) After I had imaged M42, I parked my scope for the night (put it in the home position). I turned the telescope off. Then, I manually aimed it at a part of the Northern sky with not a lot of stars. Then I took 7 one minute images of the sky, letting the stars trail. I wound up with 7 images with short star trails in them, but then (and here’s the magic), in DeepSkyStacker, I used those images as my flats and told it to use “Median” when combining them. That way, since the stars don’t trail in exactly the same places in each image, the star trails are ignored since they won’t be the median color value for that spot on the image. Now I do want to take a bunch more – probably around 20, since I noticed when it stretches those flats, there can be a bit of trailing visible anyway, but if I have more images, I believe it should go away. The difference, though, was immediately apparent.

    Comment by Ed — February 1, 2009 @ 12:29 am

  4. Okay, so these one minute flats were taken in the dark with the same ASA setting as your subs? I’m just surprised because everything else I’ve read about flats seem to happen at dusk, have to be a flat white background, have to be in a certain part of the histogram, etcetera. Were they one minute flats because that was exactly the same exposure your subs were? Thanks for the info.

    Comment by Pierre — February 2, 2009 @ 12:58 pm

  5. Yes, exactly – I’ve read a large amount about flats as well and heard the same things. I even built a light box that fits over the front of my scope, but I could never figure out how to get them to work right. But in terms of what flats do, I think this method should work really well.

    Comment by Ed — February 2, 2009 @ 1:49 pm

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