Bias and Flats

[woodblock]

With my old DSLR I used to make darks, flats and bias calibration frames but I'm having some problem making bias and flats with the ASI1600.

 

Starting with BIAS. The way I did it before was to black everything out and use the highest speed the camera had, 1/4000th in that case.  But using APT with the new camera the highest speed you can set is 1/4s although it does have a 0.000 setting which I don't know what that means. Do I need to make bias frames at all?

 

With the flats I have an LED light panel which I used for the DSLR and then adjusted the exposure so that the values were about 2/3 maximum. But with the ASI1600 even with the light turned down as far as it will go at 1/4s exposure the frame is saturated. How do other people do this? Do you just point the scope at a blank bit of wall?

 

Cheers

Steve

 

[paul]

Reading around the web you will find that people gave up on Bias frames entirely for the 1600 as short exposures were too variable. You can choose to ignore them completely because they are coolled cameras with no serious FPN (I did for a a year or two with no major issue except at Gain 0!) or do as most (including me as a recent convert) and create Dark flats. That is darks taken with the same exposure/gain/cooling as the Flats.

 

The second approach simplifies processing.

 

 

[woodblock]

Thanks Paul,

 

I did a bit of searching and found the same thing. No bias, use dark flats instead.

 

I managed to get the flats done by using the led light panel but with a few sheets of heavy drawing paper under it. That allowed me to use a 2 second exposure.

 

 

[paul]

I also use an A3 LED drawing panel with a sheet of white door panel PVC in front to reduce it further. Recently I modded it so that NiNA can generate controlled exposures. I settled on a fixed 0.5 second (that's long enough to avoid the short exposure problems) exposure and NINA works out how bright to set the panel.

 

Having a fixed exposure means you only need one set of dark-flats which you can keep for a while.

 

 

Edited April 8, 2022 by paul

[len2376]

On 4/8/2022 at 1:59 PM, woodblock said:

Thanks Paul,

 

I did a bit of searching and found the same thing. No bias, use dark flats instead.

 

I managed to get the flats done by using the led light panel but with a few sheets of heavy drawing paper under it. That allowed me to use a 2 second exposure.

 

 

Same here, works fine for me on the panels lowest setting and two sheets of printer paper (~2secs). NINA warns using the wizard if it is too bright.

[ApophisAstros]

On 4/8/2022 at 1:59 PM, woodblock said:

Thanks Paul,

 

I did a bit of searching and found the same thing. No bias, use dark flats instead.

 

I managed to get the flats done by using the led light panel but with a few sheets of heavy drawing paper under it. That allowed me to use a 2 second exposure.

 

 

Absolutely agree , thats what i have done for a long time with very good calibration. Also i dither in APT so no Darks either.

Roger

[ApophisAstros]

On 4/8/2022 at 1:59 PM, woodblock said:

Thanks Paul,

 

I did a bit of searching and found the same thing. No bias, use dark flats instead.

 

I managed to get the flats done by using the led light panel but with a few sheets of heavy drawing paper under it. That allowed me to use a 2 second exposure.

 

 

Do you use the Flat tool in APT as it should work out the correct exposure , set ADU as 25000, but experiment to adjust.

Roger

[woodblock]

I found some information on Cloudy Night about how to use Dark Flats. It said you should do it like this -

 

1 Make a master dark: Integrate the dark frames to make the master dark.

 

2 Make a master dark flat: Integrate the dark flat frames to make the master flat dark

 

3 Make the master flat as follows:

3.1 Flats - master flat dark to make calibrated flat frames

3.2 Integrate the calibrated flat frames to make the Master Flat

 

4 Calibrate the light frames as follows : (light frame-masterdark)/master flat -  to give a set of calibrated light frames.

 

I'd be interested to hear your comments on this procedure. I use MaximDL and I usually do the calibration by simply giving it a set of darks, flats, bias and lights and then clicking on calibrate and off it goes and does it so I don't usually get involved with the nitty gritty of calibration. Now I've adapted my calibration procedure in light of the information I got from cloudy nights. The person who posted the procedure on cloudy nights was insistent that this was the one and only correct way to do it but I don't have the expertise to understand the subtleties.

 

 

 

[woodblock]

1 minute ago, ApophisAstros said:

Do you use the Flat tool in APT as it should work out the correct exposure , set ADU as 25000, but experiment to adjust.

Roger

Hi Roger, I haven't used the Flat Tool in APT yet. I just adjust the exposure to put the histogram somewhere in the upper half.

[ApophisAstros]

45 minutes ago, woodblock said:

Hi Roger, I haven't used the Flat Tool in APT yet. I just adjust the exposure to put the histogram somewhere in the upper half.

Once you try it you will never go back as i didn`t.

Roger

[paul]

4 hours ago, woodblock said:

I found some information on Cloudy Night about how to use Dark Flats. It said you should do it like this -

 

1 Make a master dark: Integrate the dark frames to make the master dark.

 

2 Make a master dark flat: Integrate the dark flat frames to make the master flat dark

 

3 Make the master flat as follows:

3.1 Flats - master flat dark to make calibrated flat frames

3.2 Integrate the calibrated flat frames to make the Master Flat

 

4 Calibrate the light frames as follows : (light frame-masterdark)/master flat -  to give a set of calibrated light frames.

 

I'd be interested to hear your comments on this procedure. I use MaximDL and I usually do the calibration by simply giving it a set of darks, flats, bias and lights and then clicking on calibrate and off it goes and does it so I don't usually get involved with the nitty gritty of calibration. Now I've adapted my calibration procedure in light of the information I got from cloudy nights. The person who posted the procedure on cloudy nights was insistent that this was the one and only correct way to do it but I don't have the expertise to understand the subtleties.

 

 

 

Yes, that is the correct sequence if not using Bias frames. It is why I use the automated scripts in PI. Running scripts means I don't forget to do each step. I'm not familiar with MaximD.