Results 1 to 5 of 5
  1. #1
    Join Date
    Sep 2006
    Location
    I live in Massachusettes; Observatory in New Mexico
    Posts
    448

    Default Flats at ambient temp

    Hi!

    I recently had a discussion with a fellow concerning flats. He is of the opinion (and the tests to prove it) that flats can be taken at any temperature and need not be taken at the temperature of the target lights. Have I been wasting time these past years taking flats with a cooled CD? Is anyone out there not using cooled flats? and can you explain why this works?

    thanks

    ..george

  2. #2
    Join Date
    Oct 2005
    Location
    Strongsville, OH
    Posts
    1,548

    Default

    Hi George,

    I've read that dark-subtracting flats isn't a very good idea. Flats are already pretty short so there's very little dark-current noise to subtract out. This would be true at all temperatures. For these short exposures, the read noise dominates. As I understand it, in these conditions you actually end up adding to the noise when you dark-subtract versus reducing it. It follows, then, that the camera temperature when the flats are taken is pretty irrelevant since temperature-induce dark current is very low with short exposures.

    I set my camera temperature to what should be OK when it's imaging later in the night and don't really care whether the camera has reached that temperature or not when the flats begin. I don't see any difference in results if the flats end up being taken at a higher temperature (say 5 to 10 degrees C) than the lights.

    FWIW.

    Jim

  3. #3
    Join Date
    Sep 2006
    Location
    I live in Massachusettes; Observatory in New Mexico
    Posts
    448

    Default

    Thanks Jim,

    So no darks for the flats. Sounds like you do bias calibration. Your argument makes sense. Will make dusk flat acquistion much easier.

    George

  4. #4
    Join Date
    Nov 2005
    Location
    Scottsville, Virginia
    Posts
    1,104

    Default

    With the usually short exposure times of flats, I've never used darks for them. In fact I'd expect the flat to be noisier if you did use a dark.

    I usually do my flats like I do darks. I build a library for the season. I know from having a rotator that ACP will do East/West flats dividing the number needed in half to give both but have yet to use anything more than my East flats. Now maybe my system is really clean but I can't say that's true as I do have dust doughnuts but the flats work fine. And I use them for several months. Usually till I take a new series of darks. For summer, I usuall do darks at 0, -5, -10, -15 and winter, -20, -25, -30, and -35. It's always worked well for me and reduces the amount of work.

    Your milage may very.

    Best,
    Steve
    http://www.astral-imaging.com

    Scottsville, Virginia
    ACP Expert
    AP1200GTO
    Tak EM200
    AP 92mm Stowaway
    OGS 12.5" RC
    TAK FSQ-106ED
    STL-11000M/CF8
    ST10XME/CFW8
    Pyxis 3" Rotator

  5. #5
    Join Date
    Oct 2005
    Location
    Mesa, AZ
    Posts
    27,936

    Default

    Great suggestions, Steve. Thanks for the inputs!!
    -- Bob

 

 

Thread Information

Users Browsing this Thread

There are currently 1 users browsing this thread. (0 members and 1 guests)

Similar Threads

  1. Maxim dl sensor temp
    By George Sjoberg in forum Hardware/Software/Driver Topics Not Directly Related to Our Software
    Replies: 3
    Last Post: Mar 7, 2013, 15:22

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •