Darks, flats & bias settings for ASI2600 osc

[Ouroboros]

Just acquired an ASI2600 osc camera as an upgrade from my Canon 450D.  Yay!   I’m controlling it with an ASIair Pro (also new). 

What are the recommended settings for calibration frames?  I’m pretty familiar with doing these with my DSL, but I think maybe a dedicated cmos might be different.

Darks - ok, I’m pretty much ok with these. Same temp, duration and gain as the lights. Is it worth bothering if I’m going to dither?

Flats - what’s the optimum exposure length? I’ve read that ASI cameras don’t give the best image for exposures shorter than 2s. The ASIair has a nice routine for Flats using an automatic exposure, which can be up to 10s long. I assume I just set up the light intensity to provide an exposure for flats to be between 2s and 10s. Is that about right? 

Bias - should these be taken with as short exposures as possible in the same way as with DSLR? 

[smashing]

13 minutes ago, Ouroboros said:

Just acquired an ASI2600 osc camera as an upgrade from my Canon 450D.  Yay!   I’m controlling it with an ASIair Pro (also new). 

What are the recommended settings for calibration frames?  I’m pretty familiar with doing these with my DSL, but I think maybe a dedicated cmos might be different.

Darks - ok, I’m pretty much ok with these. Same temp, duration and gain as the lights. Is it worth bothering if I’m going to dither?

Flats - what’s the optimum exposure length? I’ve read that ASI cameras don’t give the best image for exposures shorter than 2s. The ASIair has a nice routine for Flats using an automatic exposure, which can be up to 10s long. I assume I just set up the light intensity to provide an exposure for flats to be between 2s and 10s. Is that about right? 

Bias - should these be taken with as short exposures as possible in the same way as with DSLR? 

So...i've been looking at this over the past couple of days.

1) Darks - A lot of people saying they aren't needed...I processed the image in my other thread with and without...didn't seem to make a huge amount of difference but it was only a quick edit to see what was in the data....tbh they are something to be done on a cloudy day so may as well

2) Flats - I believe the short exposure times were an issue on the other ZWO sensors, this one is apparently ok...that being said I went with 1.75 seconds in the end...they seem to have been ok but I may try for longer and see if that makes a difference next time.

3) Bias - Consensus seems to be either do Bias or dark flats....I went with dark flats...Bias I believe should be as quick as possible which in APT for this camera is basically 0 seconds.

Just my 2p worth, your results may vary.

[The Lazy Astronomer]

30 minutes ago, Ouroboros said:

Just acquired an ASI2600 osc camera as an upgrade from my Canon 450D.  Yay!   I’m controlling it with an ASIair Pro (also new). 

What are the recommended settings for calibration frames?  I’m pretty familiar with doing these with my DSL, but I think maybe a dedicated cmos might be different.

Darks - ok, I’m pretty much ok with these. Same temp, duration and gain as the lights. Is it worth bothering if I’m going to dither?

Flats - what’s the optimum exposure length? I’ve read that ASI cameras don’t give the best image for exposures shorter than 2s. The ASIair has a nice routine for Flats using an automatic exposure, which can be up to 10s long. I assume I just set up the light intensity to provide an exposure for flats to be between 2s and 10s. Is that about right? 

Bias - should these be taken with as short exposures as possible in the same way as with DSLR? 

Congratulations on your new camera!

As your camera doesn't suffer from amp glow, darks may not necessarily be needed if you dither, however as you now have the advantage of set point cooling, darks will be much more effective at removing hot pixels and such (than with a DSLR). You can reuse darks for ages, so it doesn't hurt to build a dark library in the daytime or a cloudy night (tip: take your darks somewhere dark to avoid potential for light leaks)

There's no optimal exposure length for flats so to speak, you may find that keeping the exposure length over 1 - 2 seconds yields better results, but just aim for a mean ADU value of somewhere between 1/3 to 1/2 of maximum. Use flat darks instead of bias (no need for bias frames at all). If you leave your imaging train intact between sessions you can also reuse flats and flat darks - you should be able to get several months use out of them unless you have a particularly dusty environment.

This next point may not be an issue for you, but with my ZWO camera (not the same as yours), I found that temperature matching lights and all calibration frames gave me much better results - I was having issues with my flats not properly correcting until l did this.

[Ouroboros]

Thanks @The Lazy Astronomer and @smashing.   I haven’t taken darks for years now with my 450D. I reckoned dithering did a good enough job for the time I had available. It always seemed a waste of good imaging time to take pictures of nothing. As you say, TLA, I can now build up a darks library at set temps and for different exposures. 

The Flats option in the ASIair has an auto exposure routine. It takes a few test shots to determine an exposure that gives about the right ADU value and then shoots and saves the set of flat frames at that exposure. I think that’s quite neat. 

To me it seems as easy to take bias frames as dark flats. But I am intrigued that they are equivalent. I use PixInsight to process. I am a bit unclear as to how you would use dark flats as bias. Presumably you use them to make a master bias. But then do you use them twice? Once when making a master flat and again when making a master dark? I seem to recall that PS is a bit fussy about using the same calibration files twice. I must say I’ve never used dark flats at all in the past.  

[smashing]

@Ouroboros unfortunately I am not sure how to work it in PixInsight...I just feed DSS the files and let it do it's thing  

[sterec]

You use the dark flats to calibrate the flats and then make a masterflat.  Then you use the masterdark and masterflat with no masterbias to image calibrate the light frames.

[tomato]

I agree the consensus is to use darks, flats and bias calibration frames with CCD and DSLR cameras, and flats, flat darks and darks for CMOS cameras.

The reasons behind this are discussed in this thread:

 

Edited August 14, 2021 by tomato
Link to thread added

[StuartT]

4 hours ago, Ouroboros said:

Just acquired an ASI2600 osc camera as an upgrade from my Canon 450D.  Yay!  

Me too! Though I have yet to actually use it! So this thread is super useful for me... thanks for asking the question!

[Ouroboros]

13 minutes ago, StuartT said:

Me too! Though I have yet to actually use it! So this thread is super useful for me... thanks for asking the question!

Good luck when you get the chance. I have managed a ‘first light’ with the ASI2600, ASIair and new guide camera - albeit under misty skies.  It was enough to check it all works anyway.  

[Ouroboros]

1 hour ago, tomato said:

I agree the consensus is to use darks, flats and bias calibration frames with CCD and DSLR cameras, and flats, flat darks and darks for CMOS cameras.

The reasons behind this are discussed in this thread:

 

OK - to summarise just to get me head straight on this. Looking at that pink chart above (which I’ve printed out) wherever it shows Master Bias MB frame we replace that with Master Dark Flat MDF frame.  The only exceptions being of course that we don’t subtract anything from the Dark Flat Frames (column 3). We just combine those to create a Master Dark Flat frame. And we only subtract the Master Dark Frame from the Light frames (column 5) because we don’t  have a Master Bias frame. 

[tomato]

1 hour ago, Ouroboros said:

OK - to summarise just to get me head straight on this. Looking at that pink chart above (which I’ve printed out) wherever it shows Master Bias MB frame we replace that with Master Dark Flat MDF frame.  The only exceptions being of course that we don’t subtract anything from the Dark Flat Frames (column 3). We just combine those to create a Master Dark Flat frame. And we only subtract the Master Dark Frame from the Light frames (column 5) because we don’t  have a Master Bias frame. 

Sounds good to me. For the QHY268c (same sensor as your camera) I use APP to calibrate the lights and enter a master dark, dark flat and flat.