Calibration Frames for different Gain & Offset settings.

[souls33k3r]

Hi All,

I've never investigated in to this subject matter but would like to have your opinion on this.

As we know you can change the gain and offset settings for almost all of these ASI cameras, so does that mean you have to take separate calibration frames (darks & flats) for different gain and offset settings too?

Thanks in advance.

[vlaiv]

Darks - yes, flats - no

Darks will depend on both gain and offset settings, and it will mess up your calibration to have them with different settings.

Flats are about light hitting the sensor - percentage of light being recorded by pixel - like combined QE of sensor and scope (vignetting and dust included) - so it does not depend on gain or offset (in theory). I don't think that gain or offset could change QE of pixels, but what might happen is some sort of clipping somewhere - but that would manifest it self in calibration anyway - calibration would be off in this case.

[souls33k3r]

Excellent. Cheers for the input @vlaiv. This makes complete sense.

[andrew s]

1 minute ago, vlaiv said:

Darks - yes, flats - no

Darks will depend on both gain and offset settings, and it will mess up your calibration to have them with different settings.

Flats are about light hitting the sensor - percentage of light being recorded by pixel - like combined QE of sensor and scope (vignetting and dust included) - so it does not depend on gain or offset (in theory). I don't think that gain or offset could change QE of pixels, but what might happen is some sort of clipping somewhere - but that would manifest it self in calibration anyway - calibration would be off in this case.

Flats yes.

To get at the QE of the pixels you need to subtract the offset.

Regards Andrew 

[souls33k3r]

1 minute ago, andrew s said:

Flats yes.

To get at the QE of the pixels you need to subtract the offset.

Regards Andrew 

So what you're saying that i'll need a new set of flats as well then andrew?

[vlaiv]

1 minute ago, andrew s said:

Flats yes.

To get at the QE of the pixels you need to subtract the offset.

Regards Andrew 

Once created master flat has bias / flat dark removed - you can reuse master flat without need to re do it, provided that you did not change optical layout and no dust settled in the mean time, right?

[andrew s]

Just now, vlaiv said:

Once created master flat has bias / flat dark removed - you can reuse master flat without need to re do it, provided that you did not change optical layout and no dust settled in the mean time, right?

Yes

Regards Andrew 

[andrew s]

4 minutes ago, souls33k3r said:

So what you're saying that i'll need a new set of flats as well then andrew?

No, provided nothing changes in the optical train and the flat was processed as in vlaiv's post.

Regards Andrew 

[vlaiv]

29 minutes ago, souls33k3r said:

So what you're saying that i'll need a new set of flats as well then andrew?

What Andrew wanted to say is that if you have bunch of flats without flat darks removed, still unstacked, and you lost your corresponding flat darks and you change gain / offset and redo flat darks - it will not work. But if you have your master flat created - meaning you took flats and flat darks, stacked each, subtracted them and saved only resulting master flat - you don't have to re do it.

[souls33k3r]

ah ok. 

Cheers for the info and help lads. 

Much appreciated