Resolved Flat frames and Darks

Discussion in 'STX and STXL' started by Anders Hörberg, Jul 28, 2020.

  1. Anders Hörberg

    Anders Hörberg Cyanogen Customer

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    Hi Guy´s

    Have got my beloved 107 ED APO Refraktor with 520 mm FL and F4.8 up and running with the STXL 11002 and FW8 = nice :) ... lovely coverage even if it´s a bit bad pixel compensation :)

    Whats the suggestion for range considering Flats? some say 20-32000 others around 35000 etc, also when shooting these i always used sky flats, or that is.... a matte white board in 45 degree a meter or so from the lens wich is covered in a white cloth..

    However this means reasonably short exposures with the APO, around 1.4- 5 sek depending on filter, however if i´m gonna use darks to calibrate the flats with the same exposure in Maxim - if you go under approx 2 sec, the dark isent a dark anymore, its illuminated with the xtxl

    How do you guy´s approch this matter?

    BR

    / Anders
     
  2. Doug

    Doug Staff Member

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    Personally I tend to aim a little higher for ADU level on the flats. 30-40k is a good range. Less noise that way, but you're still nowhere near any linearity issues.

    Flat-darks are absolutely the way to go. You may see a vertical gradient on the dark frames, especially on very short exposures, because of the difference in dark time between the top and bottom of the image (dark current continues to accumulate after the shutter is closed). The effect will be smaller with more cooling. This isn't a problem because the light frame has the same gradient (usually it's just not obvious).
     
  3. Anders Hörberg

    Anders Hörberg Cyanogen Customer

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    Hi Doug, Thanks i´ll try to see what i can get :)

    Looking at the enclosed pic, this is a dark from the STXL with 1 Sek exposure, will this still work?

    BR

    /A
     

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  4. Doug

    Doug Staff Member

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    Uh... no, that's a mess. You appear to have a major light leak in your system...?
     
  5. Anders Hörberg

    Anders Hörberg Cyanogen Customer

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    Hi again, not sure, dont think so i covered the whole thing in black plastic, if i go for 10 sek cooled it looks like this.. Covered

    Also you guy´s had me do something to the camera back in 2013, loosen a cable or moving some jumpers, something to do with blooming i think
     

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  6. Doug

    Doug Staff Member

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    That "dark frame" is completely saturated at 65,535.
     
  7. Anders Hörberg

    Anders Hörberg Cyanogen Customer

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    Is there something wrong with the camera? - enclosed a 2min light frame camera covered
     

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  8. Colin Haig

    Colin Haig Staff Member

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    Any chance this is a shutter problem?
    Have you had a look down the nose of the camera to see if the shutter is properly closed when doing the dark?
     
  9. Doug

    Doug Staff Member

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    The dark frame with the camera covered looks just fine. Either there's a bad light leak somewhere or the shutter isn't working.

    FYI, these cameras are incredibly sensitive. If you're trying to take dark frames in full sunlight, the shutter won't be enough to make it completely dark inside.
     
  10. Anders Hörberg

    Anders Hörberg Cyanogen Customer

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    Hi guy´s updated the drivers, and rebooted, now a 10sek dark looks like this
     

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  11. Anders Hörberg

    Anders Hörberg Cyanogen Customer

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    does that seem right
     
  12. Anders Hörberg

    Anders Hörberg Cyanogen Customer

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    And a 10 sek dark in minus 20
     

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  13. Doug

    Doug Staff Member

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    Yes those look okay.
     
  14. Anders Hörberg

    Anders Hörberg Cyanogen Customer

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    Hi Doug and also Colin, Apperently it was the firmware in the camera that didint work properly, once updated and restarted it produced these results

    Thank you again for quick answers guy´s - it means alot when you need to discuss with someone..
    While you are online, what would you suggest for agresivness etc guiding with the built in FW8 camera?, my mount is a 10Micron HPS 1000 with my APO 522mm FL and F4.8 and are ofcourse running Maxim :)

    Thanks

    / Anders
     
  15. Doug

    Doug Staff Member

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    It really depends on the equipment, and I've not used that specific combination. It has little to do with the camera - more to do with the mount, image scale, weight loading, etc.

    I would use the lowest value that allows it to keep up with the periodic error and/or drift. Usual range is 3 to 8; try starting at 5.
     
  16. Anders Hörberg

    Anders Hörberg Cyanogen Customer

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    Ok Thanks guy´s

    BR

    / Anders
     

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