Share:
Notifications
Clear all

19 June 2021: Our upload server https://upload.astropixelprocessor.com/ has been migrated successfully to our new office with higher upload and download speeds (nearly 10MByte/sec up/down ) ! We now have 1 general upload user called: upload with password: upload. The users upload1 - upload5 have been disabled.

31 May 2021: APP 1.083-beta2 has been released ! APP 1.083 stable will follow soon afterwards. It includes a completely new Star Reducer Tool, New File Saver Module, Improved Comet registration and much more, check the release notes here!

DOWNLOADS are available HERE!

 

Correct Vignetting  

Page 2 / 2
  RSS

(@vincent-mod)
Universe Admin
Joined: 4 years ago
Posts: 3861
September 14, 2021 19:54  

Ok, just wondering, I don't see gain 0 a lot. But things like the offset I didn't see in the header, what did you set that at?


ReplyQuote
(@marc68)
White Dwarf Customer
Joined: 2 years ago
Posts: 14
September 14, 2021 21:33  

Gain is 0 and offset 50


ReplyQuote
(@vincent-mod)
Universe Admin
Joined: 4 years ago
Posts: 3861
September 15, 2021 11:37  

Ok thanks for checking, that all seems fine. I'll continue investigating as well.


ReplyQuote
(@vincent-mod)
Universe Admin
Joined: 4 years ago
Posts: 3861
September 15, 2021 11:52  

So indeed, seeing the same. I think it must be lying in the way the flats are shot. Over-correction usually is caused by a difference between how the light enters the setup normally and when the flats setup is used. Like Wouter also mentions, it may also be worth it to shoot at a higher ADU.


ReplyQuote
(@marc68)
White Dwarf Customer
Joined: 2 years ago
Posts: 14
September 15, 2021 12:41  

Thanks Vincent, ok i will try higger adu.

 


ReplyQuote
(@mabula-admin)
Universe Admin
Joined: 5 years ago
Posts: 2728
September 29, 2021 17:36  

Hi Marc @marc68,

I am investigating your data.

Regarding the Lum data that you uploaded:

After data calibration I see the same, the vignetting profile is overcorrected in the corners. It seems that the gain and sensor offset are all okay and the same for the lights and the bias, darks and flats.

So I had a good luck at the actual calibration data and I see several issues which can and probably will explain why calibration is not working optimally 😉

First have a look at the bias and darks, this is a single dark frame where I set the Black slider to zero to see if the sensor offset is set high enough :

Dark clipping on left side of histogram

Clearly it isn't because the histogram is clipping on the left side. The Same holds for your bias frames. So that needs to be fixed and can easily be done by using a higher sensor offset using your camera's driver.

Now if I look at your Luminance flats, I see immediate problems I think, the vignetting profile is not uniform from center to the corners, it has ripples in it and that will never be okay I would expect.

Lum Bad Flat

So.. probably you will need to change/improve the way in which you make your flats for this setup. But first try to fix the sensor offset and check if things have improved 😉 already.

Will check your green data as well now.

Mabula


ReplyQuote
(@mabula-admin)
Universe Admin
Joined: 5 years ago
Posts: 2728
September 29, 2021 17:43  

Hi Marc @marc68,

Just had a look at the green flats. I see the same issue as with your lum flats, they show ripples in the vignetting profile and that needs to be solved/fixed. You expect a smooth illumination profile in the flats from the center to the corners without those ripples superimposed on it.

Green Bad Flat

Mabula


ReplyQuote
(@marc68)
White Dwarf Customer
Joined: 2 years ago
Posts: 14
September 30, 2021 13:15  

Hi Mabula, thanks a lot for having looked into this. Got your points and will apply. I was not sure about those "circles" in my flats, i guess this is what you name ripples. I will try to find out why my alnitak flip flat device does produce this and also increase offset.


ReplyQuote
(@the_bluester)
White Dwarf Customer
Joined: 3 years ago
Posts: 19
October 2, 2021 07:32  

Just to confirm something, your flats were shot at 0 gain as well? I recently had a very similar issue with my ASI2600, flats shot carefully at 100 gain (Sky flats and with a panel) looked fine and the master flat looked fine but it over corrected the corners. I reshot really rough flats at 0 gain by just guessing exposure times as the sky darkened and they corrected really nicely, so I reshot proper sky flats at 0 gain. The illumination is quite flat to begin with and all I can think of is that the 5ADC/e of 100 gain (About the same as your 6200) introduced too much quantisation uncertainty for the flats to work well. 

 

I didn't do that until after I spent quite some time looking for light leaks of course!

This post was modified 4 weeks ago by the_bluester

ReplyQuote
(@marc68)
White Dwarf Customer
Joined: 2 years ago
Posts: 14
October 2, 2021 08:40  

Hi, yes gain 0 and offset 50 for all flats. I will try the points from mabula, what i dont yet get i where those ripples on my flats are coming from. Need to check my setup. Thanks


ReplyQuote
Page 2 / 2
Share: