Background Value of Darks from my Library

[Martin Dowd]

This is a question for Han
Using ASTAP to check the background values of my Dark Library by loading my Darks ( exposure sets at a time ) into the Darks tab of the Stacking program , resulted in all exposures from 10 sec up to 300 sec having a background value of 501 in the Background column.
Is this normal as I would have thought exposure times in a Dark frame would change the value slightly ?
In addition , my Flat Darks irrespective of exposure time 0.1sec up to 4.0 sec had a background value of 501 as well.
Maybe Im not understanding what the Background value represents in the Stacking program ( I assume it represented the ADU value of the specific frame )
My camera is a 2600MM
All Darks and Flat Darks same Gain 0 or Gain 100 and temperature -10C
My Dark Library consists of 10 sec up to 300 sec ( 40 darks each set )
Gain 0 and Gain 100 sets
All temperatures -10C

Thanks and await your advice

Martin

[han.k]

Hi Martin,

I see the same for my ToupTek camera having the same Sony IMX571 sensor. The dark value of short exposures and longer 200 seconds have all the same value 101 due to the very low dark current. The dark current is something like 0.003 e-/sec. So for unity gain you maybe see an dark value increase if you exposure longer then 300 seconds. Or if you raise the sensor temperature. Then the dark value will increase by time.

For these Sony sensors the dark exposure duration doesn't matter as it used to be in the past except for maybe the hot pixels. So it is still a good practice to use the same exposure time for lights and darks.

You could test your camera sensor with SharpCap or CCDCiel program:

Dutch language:
https://www.astroforum.nl/threads/new-sensor-analysis-tool-in-ccdciel.1477031/#post-1559484

Han

[Martin Dowd]

Thanks Han,
I assume you mean't 501 not 101 ???
I dont usually expose longer than 300 sec in Narrowband ( only 30 sec to 120sec in Broadband ) so the Background values will probably be 501 all the time.
I always match my Darks to Lights in regard to exposure time , temperature and Gain.
My Flats and Flat Darks again are matched for exposure , temperature and Gain.

Clear Skies
Martin

[han.k]

I operate my Touptek at unity gain so I have the full 16 bit range. This is nice for object with a very bright center. The darks have then a value of 101. ZWO has probably decided to set the pedestal of their 2600MM camera at 500. It is just a design choice.

[Martin Dowd]

Han,
Thanks for clarifying
Yes Ive just read the specs on the Touptek
At first glance I thought the ZWO2600MM and the Touptek 2600 were the same , obviously not.
Both excellent cameras in any case

Cheers
Martin