Dusk Flats West of Merdian and Lights both E/W of Merdian

Discussion in 'Image Capture' started by Phillip Marshall, Dec 12, 2016.

  1. Phillip Marshall

    Phillip Marshall Cyanogen Customer

    Joined:
    Oct 12, 2014
    Messages:
    4
    Location:
    San Diego East County
    I have been using MDL for 8 years and using Flats for the past 5 years with good results.
    But I am wondering about taking dusk flats west of the merdian and taking Lights both East and West of the Meridian. I have been letting MDl apply my dusk flats to lights from both sides of the meridian during Stacking.
    Results have been good.

    All my night sessions are orchestrated by CCD Commander, along with MDl, FocusMax, TheSkyX. MDl does camera control, observatory control and AutoGuiding. CCDC also does my Flats, usually sunset flats

    When a Meridian Flip occurs, camera orientation in relation to the sky is reversed (I think). If I want to compare an image taken in the east with one taken in the west, to match them up, I must use Flip and Mirror commands.

    I am wondering, should I only apply flats taken in the west to only lights taken in the west with seperate flats taken in the east with lights taken in the east?

    I am quessing that I can apply flats taken in the west to lights taken on both sides of the merdian.
    But trying to figure out what is correct is a bit to much for my old thinker.

    What is the accepted and best practice?
    Thank you fellow night sky gazers.
     
  2. Colin Haig

    Colin Haig Cyanogen Customer

    Joined:
    Oct 27, 2014
    Messages:
    937
    Flats are flats, unless your optical train "flops" when you flip meridian side. e.g. if you have an SCT, the mirror may flop a bit from one side to the other, and thus the dust donuts may appear to move a bit. Why not compare a couple of flats you take on either side? If the weight of the camera etc causes a shift relative to the optics, then you might want to do so as well.
    Taking it to an extreme, do a flat at every possible orientation ;-)
    Realistically, I take one set of flats, at a standard position where I have a flat panel. I've pretty much locked down the main mirror, and don't have a lot of extra slop. So one flat works for me. The more talented folks who are truly OCD may wish to do more.
     
  3. Ross Salinger

    Ross Salinger Cyanogen Customer

    Joined:
    Oct 10, 2014
    Messages:
    143
    Location:
    Carlsbad Ca
    That's fine if the optical axis is perfectly centered or if the chip is so small that being a bit off center doesn't matter. Otherwise your object will shift and the fall off will give problems in your flats when you flip the mount. I noticed this when I went to a big chip camera and found that I wasn't perfectly centered. I never noticed it with the small 8300 chip because the edges of my optical train weren't involved.
     

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