How to use bias frames?

[muletopia (Chris)]

After several years of pre-processing with Nebulosity I have now tried to use bias frames.


I want to apply them to 10 minute lights taken with a QHY8l at gain zero.
So I tried 20 bias frames of 0.001, 0.01, 0.1 and 1 seconds.
Each set stacked and used in four preprocessing runs of Nebulosity
(darks and lights both 600 seconds).


The result is a hideous mess,black background, no detail and prominent hot pixels.


Google has any number of entries on how to take bias frames but I could not find any on how to use them.


To ask a beginners question, I am obviously missing something. What?


Chris

[Startrek (Martin)]

I’ve learnt from entering the new world of Calibration last year that it’s not one shoe fits all. All cameras are different , all telescopes are different and stacking software is different so in my case it was exhaustive trial and error after a few months to finally nail the best outcome.
I use a 2600MC in various Newts and found that you need the right dark subtraction to calibrate your Flats correctly or else yes your image will be a mess.
I guess I’m lucky my 2600MC doesn’t require Darks as the dark current at -10C is negligible
Your Flats must be captured correctly too ( between 1/3 and 1/2 on the Histogram) based on your cameras ADU
I tried all calibration combos
Lights , Flats , Darks
Lights , Flats , Dark Flats
Lights , Darks
Lights , Flats , Bias

The calibration method that finally worked for my scope, camera and stacking software DSS was Flats and Bias. Eliminated vignetting, dust donuts and created a nice flat even field
I take my Bias frames at night with lid on the Newt , a black shower cap over the base to stop any stray light with the following settings
Exposure time - minimum exposure setting for my camera which is 0.000032 sec
Gain - same as Light frames
Off set - same as Lights
Focus - same as Lights
Temperature - same as Lights
Quantity - minimum of 50

My Flats are taken with a Huion A3 LED dimmering light panel and white T shirt stretched over OTA
My cameras 16bit ADU range is 0 - 65,536 so I try to set the brightness on the panel so I end up with an ADU range of say 8500 to 34000 on a flat frame
I use the Flats Aid in APT to capture my Flats and Bias frames
Without a filter Flats are usually 1 to 3 sec
With a NB filter Flats are usually 5 to 10 sec

Then I use Deep Sky Stacker (free) to stack my frames which is pretty much self explanatory and automatic
Lights
Flats
Bias

My stacked image when stretched in Startools works out spot on each time, no vignetting, dust donuts and a nice even flat field

Took me at least 2 months to sort out Calibration

To throw another curly one into the mix , guys with the same camera but say different scope find Flats calibrate better with Dark flats and Darks etc.. Not Bias just to confuse things

Hope the above helps in some way

Cheers
Martin