Vignette issue on altair 1600m

[Marmo720]

Hi all,

I have made the jump to mono with altair hypercam 1600m, combined with 36mm filters and ZWO 7 EFW. I have the train setup to the spacing given for the altair 1x flattener on my Wave 80 ED. To the best of my ability anyway...

The link below shows a DSS stack of:

60 x 60 sec lumi at gain 500

50 x 60 sec darks 

58 x 0.3sec bias 

50 x flats at 2000 ADU

All are at -15 deg. The camera is 12 bit and I thought 50% would be 2000 ADU. Equivalent to about 30K on a 16 bit camera. 

I have tried half the number of flats. I have tried ADU ranging from 800 to 2000. All give me very similar results to the below image. 

Stuck for what to do so appreciate any advice.

https://we.tl/t-pA4rzIxaMb?src=dnl

 

Edited May 17, 2020 by Marmo720

[jjosefsen]

Hi,

I doubt this is vignetting, your images should be getting darker not brighter around the edges.

Try calibrating without flats, does your issue persist? I'm going to guess that they are - because I have the same problems with the same camera.

It seems to be in the dark frame calibration and for me it is only a problem with broadband filters..

But I would love to see what happens if you try to calibrate without flats and compare, and without darks and compare.

[Marmo720]

On 26/04/2020 at 23:42, jjosefsen said:

Hi,

I doubt this is vignetting, your images should be getting darker not brighter around the edges.

Try calibrating without flats, does your issue persist? I'm going to guess that they are - because I have the same problems with the same camera.

It seems to be in the dark frame calibration and for me it is only a problem with broadband filters..

But I would love to see what happens if you try to calibrate without flats and compare, and without darks and compare.

Thank you for the response. Happy to know it isn't something specific to my setup - gives me hope

I have attached the same data but without flats (with darks + bias), and without darks (with flats + bias), and lights only (no calibration).

I do have some Ha data from tonight and will do same with that to see what the results look like.

How do you overcome this issue with your camera? What settings do you use for gain, offset, ADU for flats?

Thanks again!

 

Edited May 17, 2020 by Marmo720

[RolandKol]

I just stretched the initial "Autosave.fits" file to show as example for audience. No crop.

This one is autostreched on pix without any background adjustments:

 

The second, -  Background Subtracted only:

 

The third, - Background Divided and Normlised, later Subtracted.

 

I would say, - not perfect, but good enough....
 

P.S.
Mo, is this one the same, -  from the cloudy night?

Asking, as on my Office PC, - after background extraction it looks even better than at home .

Edited April 27, 2020 by RolandKol

[RolandKol]

14 hours ago, Marmo720 said:

58 x 0.3sec bias 

Also, try to take more of them... 100 - 150.

And what about DarkFlats.... Have you managed to collect them?

Edited April 27, 2020 by RolandKol

[RolandKol]

Also,

I think it is worth to mention, - if I recall correctly, Mo did Darks and Bias via APT on Windows,

Lights and Flats, - via EKOS/Kstars on the RaspberryPi.

 

 

[Marmo720]

1 minute ago, RolandKol said:

Also,

I think it is worth to mention, - if I recall correctly, Mo did Darks and Bias via APT on Windows,

Lights and Flats, - via EKOS/Kstars on the RaspberryPi.

 

 

Yes, thought that might be issue so I will retake a new set of bias, darks and dark flats today before the rains come in and see if that makes a difference. 

The M51 data I attached are from clear night without clouds. 

 

[RolandKol]

18 minutes ago, Marmo720 said:

Yes, thought that might be issue so I will retake a new set of bias, darks and dark flats today before the rains come in and see if that makes a difference. 

The M51 data I attached are from clear night without clouds. 

Just check your very first dark taken during a daytime...
In my case, - if camera is on the scope, darks are not completely dark even if the whole rig is covered and etc.

[Marmo720]

Below link for the master files if that is useful. Is the master dark ok? 

https://we.tl/t-XG1Jmo2rMZ?src=dnl

[ollypenrice]

Rather than asking folks to download the originals, I think you'd get more interest if you just made JPEGS of the files and showed them here. For the purposes of showing what's going on this would be fine.

My understanding is that the CCD trick of using a master bias as a Flat Dark (a dark for calibrating your flats) does not work. You need to shoot Flat Darks at the same settings as your flats.

As Roland said, the third image in his post is pretty flat.

Olly

[Marmo720]

2 hours ago, ollypenrice said:

Rather than asking folks to download the originals, I think you'd get more interest if you just made JPEGS of the files and showed them here. For the purposes of showing what's going on this would be fine.

My understanding is that the CCD trick of using a master bias as a Flat Dark (a dark for calibrating your flats) does not work. You need to shoot Flat Darks at the same settings as your flats.

As Roland said, the third image in his post is pretty flat.

Olly

Thanks Olly. I assumed people would prefer the raw masters to check but will do JPEGs going forward. 

Good to know regarding dark flats instead of bias as I come from Canon which worked fine with bias. I have tried the stack with dark flats and no luck. 

I am planning to do a clean capture session starting over just to make sure I haven't missed anything. 

Does anyone here have the Altair 1600m and can help with what settings they use? Would be very helpful and appreciated.

Thanks 

 

[ollypenrice]

4 minutes ago, Marmo720 said:

Thanks Olly. I assumed people would prefer the raw masters to check but will do JPEGs going forward. 

Good to know regarding dark flats instead of bias as I come from Canon which worked fine with bias. I have tried the stack with dark flats and no luck. 

I am planning to do a clean capture session starting over just to make sure I haven't missed anything. 

Does anyone here have the Altair 1600m and can help with what settings they use? Would be very helpful and appreciated.

Thanks 

 

I'm giving the standard and wholesome advice but let me tell you that I used a rig over a two-year spell in which over-correcting flats were a persistent nightmare and which we never really fathomed. We found a solution which worked for a while and which, overnight, suddenly stopped working. Sometimes this game is beyond reason...

Olly

[Marmo720]

50 minutes ago, ollypenrice said:

I'm giving the standard and wholesome advice but let me tell you that I used a rig over a two-year spell in which over-correcting flats were a persistent nightmare and which we never really fathomed. We found a solution which worked for a while and which, overnight, suddenly stopped working. Sometimes this game is beyond reason...

Olly

I hear that! I learnt the same with my canon and doing flats. Worked well for a bit, then flats stopped until I figured out why after weeks of trial and error. 

Frustrating but when it all works, very addictive!