Flats and Bias setup

[bluesilver]

Hi, So just another question on getting up and running with flats and bias and how to put these into live stacking.
The camera is asi2600mc ( Colour camera )
I see the camera tab that there is the capture flats tab, this is what is used.
It reads like you set the exposure so that the white histogram is around the 60% mark and the green histogram is around the 90% mark and not clipped at the right hand side.

But am i correct in saying that with flats, you should always use the same gain as what you are using for your light images? ( + same focus and temperature )
So with my camera it is either gain 0 or gain 100 nothing else really, I have seen some youtube videos where they are winding the gain up or down wildly for their flats compared to what their lights were taken at, I could be wrong, but i think that is wrong and gain is suppose to be the same from lights, flats, bias.

So after i get the flats setup and take say 50 of them, how are the bias taken?
I have yet to see a video on this.
The flats capture tab just says: Capture and subtract bias frames to correct for black level offset in flat.
Or is that just it, click this and it captures my 50 flats and automatically dose the bias frames?

After all this, Is there a way to add these flats and bias to the live stacking, or is this done automatically also?
I can't really find an answer for that one,, but everyone appears to be taking he flats / bias and then staring the live stacking, but no mention of what happens to the Flats/bias or how it is added o the live stacking

Sorry for all the questions, but very keen to try this out, always finding new things with SharpCap and that is great.


I do use the program Astrophotography Tool for plate solving and autofocusing, + pretty much everything else, but really want to move more into SharpCap as it appears to be more user friendly + has in my opinion better tools.

But any advice on these questions would be greatly appreciated.
Thanks.

[calan]

You don't need to use the same gain for your flats as you do for the light frames. In fact, I usually shoot one master flat after I get focused, and then use that same flat for various gains and exposures during the night, depending on the target and conditions.

I have a profile set up for flats that I use every time, with an LED light panel. I have the gain and exposure set to give me a nice signal at about 60%, and just capture a quick 50 frames.

Or is that just it, click this and it captures my 50 flats and automatically dose the bias frames?

Yep, that's it. If you check the bias option, SC does everything for you.

To use the flats, there is a drop-down list under the pre-processing section where you can select the master flat that you create. Same area where you select the master dark.

[admin]

Hi,

let's see...

Flats do not need to be taken at the same settings (gain or exposure) as light frames. Probably helpful to keep the offset/black level/brightness settings the same for all images though for simplicity. Flats should be taken with the same settings as dark flats (if using those) and the same settings - except exposure - as flat bias frames. Both of those will be dealt with automatically if you use the 'capture flat' option and tick the appropriate boxes.

The key thing with using flats (particularly for deep sky) is to use them with dark frames (taken at the same settings as the light frames) and with either dark flats or bias frames. If you miss out either the dark frames or the dark flat/bias then the flat correction will be wrong. (as an aside, you can sometimes get away with missing out both when using flats for solar/lunar/planetary to remove dust shadows if you expose your flats to roughly the same brightnes level as your target).

When you capture a flat frame, it is (by default) immediately added to the SharpCap 'Apply Flat' processing control, so it will be used to process each new frame from then on, including live stacking.

Hope this helps you get started,

cheers,

Robin

[bluesilver]

Thanks heaps for all these detail instructions and advice, it is very much appreciated.
Just got to get my head around this new way of doing things.
I am planning on doing 37 second exposures as that was what was recommended at 100 gain with my asi2600mc when i did that smart histogram test, i will run this evetime from now on i think.
And run it for about 2.5 hours.
From what nearly everyone is saying, with this asi2600mc camera, i only need to take Flats and Bias, no need for Dark Flats or Darks.
I will set up the Dither option as that will help to reduce any access noise also at maybe 5 minute intervals.

I will have to go back a try to find this drop-down list under the pre-processing section where you can select the master flat that you create.
I think that is one of the key things that i couldn't find information on.
This is the option under the Camera tab - pre-processing correct?
The just select apply Flat, correct?

It could be worth doing a Dark Frame also possibly, but from what people are saying, it is not needed with this camera.

So far i think i am understanding it all, definitely taking notes from when i do get a chance to put this into practice when i get a clear night
All advice is greatly appreciated.
Thanks.

[calan]

I'm not familiar with the 2600, but I have two other ZWO cameras... the ASI224MC cooled, and an ASI294MC-Pro.

In my experience, it never hurts to use darks. And it's so easy to capture and use them in Sharpcap, it's really a non issue IMO. Just cover the scope (or even the camera if it's not in the scope) on a rainy day or whatever... and create a dark library with every gain and exposure (and optionally color balance, offset, cooling, and flip) that you think you will use, and you are done. Then just include the appropriate dark in each camera profile that you set up.

NOTE: Robin has some very useful info posted somewhere about how to properly set the camera cooling based on sky conditions, but I always just lock it to -10C and roll with it. But if you want to really "do things right", I would suggest reading his info on that. It's actually a small part of a very much larger excellent conversation on managing noise, so it's a mandatory read regardless. (or maybe a watch... I forget if it was an article or video. ).

As for the gain, etc. ....

SC's histogram smart brain is very usefull, but you will find that given your particular location and sky conditions, you can generalize things and settle on a fairly simple set of parameters that will give best results. As an example, I usually end up using either 5 seconds or 10 second subs at 125 or 150 gain... depending on whether the moon is up or not, and how much wind I have.

It's always windy here, so I'm not going to get 3 hour subs; 10 seconds is usually pushing it. So, I have to work within that. Fortunately, SC and the latest generation of cameras have the tools and ability to make use of that.

[bluesilver]

Appreciate your reply and advice, I think i am getting my head around it now, just been going over a few more videos.
It appears that the darks are taken the same way as i have been doing them, so that is good unless i am mistaking it.
Basically the darks are taken at the same exact settings that you have for your lights, some exposure, gain, temp, time all that, but just with the cap on the scope.

Yes i did read through the article and video on the the temperature and how it effects the noise, for my camera, at around -10 seams to be the sweet spot for this.

So far all good with writing all this down.
Very much appreciated.

[calan]

Basically the darks are taken at the same exact settings that you have for your lights, some exposure, gain, temp, time all that, but just with the cap on the scope.

Correct.

I always just use the Capture Dark tool in SC, to create a master dark for each camera profile I'm going to use and I'm done. But you can also cover the scope and save the individual dark frames, and then stack them externally to create a master dark if you want. Set the drop down at the top middle/right to "Dark frames", and they will be tagged properly. Personally I don't see the point in all that, and just let SC do the work. YMMV of course.

One other point on darks, that was critical for me. SC has a banding suppression feature, that can help to remove bands and streaks in the noise, which is apparently caused by small voltage variances within the camera (this is a different animal than bias or walking noise). In order to get rid of it, I found the best settings for the banding suppression, and then ran my darks with it turned on. (in my case, banding threshold = 1, banding suppression = 50). That way, when I set those values in the camera profile for light frames, the dark master matches it. It made a huge difference in smoothing out the background for me.

Just be sure to capture as many individual darks as possible, to allow the banding to average out. I usually collect 100 frames for each master; but since I use short exposures not greater than 30s and rarely change any settings, it's not a big deal to create them all on a dead night.

[bluesilver]

Thanks heaps,
Very well layed out and easy to understand.
Will be giving all this a try next time i get a clear night,
Appreciated.