Jump to content

  •  

CNers have asked about a donation box for Cloudy Nights over the years, so here you go. Donation is not required by any means, so please enjoy your stay.

Photo

Flat frames and Offset (CMOS)

  • Please log in to reply
3 replies to this topic

#1 nyx

nyx

    Messenger

  • -----
  • topic starter
  • Posts: 438
  • Joined: 11 Jul 2018
  • Loc: Germany

Posted 26 September 2021 - 02:31 AM

Quick question regarding flat frames using, in my case, a monochrome CMOS camera (QHY183M): does offset need to be the same as the lights?

 

Using NINA's there is no way one can set the offset within the Flat Wizard (except on the Equipment > Camera page). The Flat Wizard allows you to define a gain value but not offset. Does NINA automatically tweak offset behind the scenes (during flat frame histogram/exposure calculation)?

 

Similar story in SharpCap. If I use my light frame settings (gain, offset, etc.) I get a warning that Too many pixels are below 10% saturation, even if the histogram looks correct (peak at 50%). Only when I increase the offset value (and slightly decreasing exposure to compensate) do I get the Histogram: OK status from SharpCap.



#2 imtl

imtl

    Skylab

  • *****
  • Moderators
  • Posts: 4,088
  • Joined: 07 Jun 2016
  • Loc: Down in a hole

Posted 26 September 2021 - 06:15 AM

Gain, offset, temperature (with darks) should match your lights. Otherwise you won't be able to calibrate properly.

Don't know what camera you are using but you can set the offset probably in the camera driver


  • nyx likes this

#3 nyx

nyx

    Messenger

  • -----
  • topic starter
  • Posts: 438
  • Joined: 11 Jul 2018
  • Loc: Germany

Posted 26 September 2021 - 08:08 AM

I went back and checked the filename of the flats I shot with NINA and yes, you are right, NINA shot them with the same offset defined in the Equipment > Camera page. I will ask in the SharpCap forums how to get past this Too many pixels below 10% saturation warning without changing the offset. Thanks!



#4 jonnybravo0311

jonnybravo0311

    Mercury-Atlas

  • *****
  • Posts: 2,566
  • Joined: 05 Nov 2020
  • Loc: NJ, US

Posted 26 September 2021 - 10:06 AM

I went back and checked the filename of the flats I shot with NINA and yes, you are right, NINA shot them with the same offset defined in the Equipment > Camera page. I will ask in the SharpCap forums how to get past this Too many pixels below 10% saturation warning without changing the offset. Thanks!

This is one of the very few issues I have with NINA. If you're providing me with a nice wizard-based way to setup and take flats, and in that process you allow me to set the gain, exposure length, filter, light panel brightness, etc, why, oh why don't you let me set the offset as well? Why do you force me to go to the equipment page and change the camera's default offset there? I mean, you allow me to enter an offset when I'm creating a sequence, so I know the code has been written and implemented elsewhere in the product ;).


  • OldManSky likes this


CNers have asked about a donation box for Cloudy Nights over the years, so here you go. Donation is not required by any means, so please enjoy your stay.


Recent Topics






Cloudy Nights LLC
Cloudy Nights Sponsor: Astronomics