AstroBKK

Flats:

(1) Tablet screen flats is inspired by Thierry Leagault flash method (see ref ref below): a sheet of paper is placed on the scope aperture ensuring it is parallel to the front lame, and a large tablet (in my case Surface pro) displaying a full white screen (Paint) at max screen brightness is placed ~30cm from scope with both the tablet's and camera's sensor diagonals aligned. The sheet must be thin enough to reach 2/3rd of the histogram, whiteboard paper works well and size is great to cut a large piece that covers the 9.25" aperture well. First few captures are checked "live" while standing in front of the scope and slightly moving the tablet, no differences between flats should be noticed. Then actual flats are acquired, keeping this position trying to limit motion is not exactly comfortable, but it is more practical than fastening a T-shirt in daylight and allows to change optical train in the course of an observation session. Definitely a flatbox would be better, I need to make or buy one.

(2) Flats can be reused if the optical train configuration and camera rotation are well recorded and reproducible. Dust specks may move from one session to another, in such a case will not be wiped off by the flat.

 

Darks:

Lengthy to acquire but easy reuse especially if settings increments are defined for all sessions. With ASI294, I typically use:

Bin: 1 / 2

Exp: 10 / 30 / 180 / 300 / 500 sec

Gain: 120 / 160 / 200

Temp: -10 / 0 / 30 (ambient) deg.C

Darks should be renewed every 6 months or more, depending how often the camera is used.

 

Bias:

Easy to capture and re-use, using same settings increments as for darks apart from temperature.

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References:

Astrophotographie (2016) by T. Legault, p33.

https://practicalastrophotography.com/a-brief-guide-to-calibration-frames/

https://starizona.com/tutorial/calibration-images/

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