Altair 26C dark frame settings

[Priesters]

Hi,

Hopefully postie will be delivering a 26C on Monday so I was wondering if any other owners could let me know about their dark frame library for this camera.  I know it’s a very broad question but just a few ideas of settings (black level, gain, exposure etc) that other people typically use would hopefully give me a good starting point to build my library from. I use SharCap as my capture software and have a couple of dual band filters - Optolong L’Extreme and L’Ultimate.  

Cheers

Andrew

[newbie alert]

Dark frames should be the same exposure length, temp and at the same setting as your lights, just with the lens cap on... Darks frames are to calibrate out the imperfections caused by the camera

The gain and offset will change using the extreme and the ultimate 

Edited March 4, 2023 by newbie alert
Added info

[Priesters]

Thanks for replying.  Yes I’m aware of the purpose of Darks 🙂.   It was just a case of trying to steal other people’s homework so I can start to build my dark frame library at a sensible point e.g. 5 min exposures work well with gain of ??, offset of ??.  Totally appreciate this will vary with conditions / targets and may well be a daft question but thought it worth asking anyway.

[Laurin Dave]

I have ZWO and QHY cameras with the same sensor and use matching Bias only for Flats and Bias plus Bad Pixel map (from a long Dark) for Lights. It works fine and saves a lot of effort.  The Dark current with these sensors is next to nothing as you can confirm when  you get it.

Dave

[david_taurus83]

I have both ASI533MM and ASI2600MC. I don't bother with darks anymore, just cool the camera and take a set of bias frames. There's hardly any dark current with them it's not worth taking darks. Dithering is a must though to remove hot pixels.

You'll always get differing opinions on this so see what works for you. 

[Priesters]

On 04/03/2023 at 10:14, Laurin Dave said:

plus Bad Pixel map (from a long Dark

Thanks for the advice.  It seems I can put Darks behind me 👍.  As others have said I will dither to remove hot pixels but I'm also interested in your mention of using a bad pixel map.  When you created this, did you use a high gain setting and what about offset?  Also was it a single dark frame or did you stack several?  

[Laurin Dave]

8 hours ago, Priesters said:

Thanks for the advice.  It seems I can put Darks behind me 👍.  As others have said I will dither to remove hot pixels but I'm also interested in your mention of using a bad pixel map.  When you created this, did you use a high gain setting and what about offset?  Also was it a single dark frame or did you stack several?  

I use a stack of 25 20 min darks taken at low gain ..  although this doesn’t matter as gain doesn’t change which pixels are bad..  I calibrate with Pixinsight and use the master dark in the Cosmetic Correction process with hot pixel rejection sigma set at 3..  Pixinsight then uses this to create the Bad Pixel map with which to correct the lights..  which it does very quickly..   

HTH

Dave

 

[gorann]

I have three ASI2600MC and use no dark or bias calibration frames (I initially made a dark library but using a master dark made no noticeable difference and I have repeatedly heard the same from others). And I do not dither. Still I rarely see a hot pixel. I think it has to do with the Image integration routine I use in Pixinsight (see below). In the rare case of a some hot pixels they are easily removed by the Dust & Scratches filter in PS (using a low setting that does not affect stars).