#1  
Old 07-03-2021, 05:39 PM
BlakPhoenix (Rohan)
Astro With RoRo

BlakPhoenix is offline
 
Join Date: Jan 2019
Location: Sydney
Posts: 17
Flats Over-Calibrating

SOLVED: Driver update changed the default offset for the camera from 0 to 8 - lead to darks not letting flats calibrate correctly.





Hi all,


I have just started working with narrowband filters on the ASI294MM. I am having a problem where my flats are over-compensating for some artefacts on the sensor instead of properly calibrating them out.


You can see in one of the original subs (img 3) there is some uneven atrefacts, especially down the bottom left/right. In the master light (img 2) you can see that this has been made lighter, but much too light! You can see what the master flat (img 1) looks like, with correctly shows the uneven surface.


I am using the WBPP script in Pixinsight, and have tried tweaking all kinds of settings with no luck in getting the calibration correct.


Any help would be GREATLY appreciated.
Attached Thumbnails
Click for full-size image (masterFlat-BINNING_2-FILTER_Ha.jpg)
72.9 KB22 views
Click for full-size image (masterLight-BINNING_2-FILTER_Ha-EXPTIME_240.jpg)
208.5 KB21 views
Click for full-size image (0003_240.00S_-10.00C_120G_5151F.jpg)
212.9 KB21 views

Last edited by BlakPhoenix; 08-03-2021 at 09:38 AM.
Reply With Quote
  #2  
Old 07-03-2021, 05:45 PM
Nikolas's Avatar
Nikolas (Nik)
Dazed and confused

Nikolas is offline
 
Join Date: May 2012
Location: Melbourne
Posts: 2,116
try DSS instead and see if that renders the same result. Pixinsight is not as good at stacking as the other stacking programs. It does everything else really well.
Reply With Quote
  #3  
Old 07-03-2021, 05:50 PM
multiweb's Avatar
multiweb (Marc)
ze frogginator

multiweb is offline
 
Join Date: Oct 2007
Location: Hinchinbrook
Posts: 20,656
You need to scale your flats with a bias frame of equal duration taken at the same temperature. This has been discussed many times before so a search on the forums should give you all the info you're looking for.
Reply With Quote
  #4  
Old 07-03-2021, 06:29 PM
Nikolas's Avatar
Nikolas (Nik)
Dazed and confused

Nikolas is offline
 
Join Date: May 2012
Location: Melbourne
Posts: 2,116
If it's a ZWO camera better to shoot dark flats rather than bias frames
dark flats are flats taken with the cap on same duration/focus etc.
Reply With Quote
  #5  
Old 07-03-2021, 06:50 PM
Alchemy (Clive)
Quietly watching

Alchemy is offline
 
Join Date: Jul 2007
Location: Yarra Junction
Posts: 3,030
Ooh thatís a problem

One Iíve never had.

Lights, Darks, Flats, Dark Flats, Bias.

I use them all and DSS asks for them all, despite what gets said from time to time.

Lights .... obvious but shoot to a consistent temperature
Darks..... same time and temp as lights with cap on , I use 30
Flats..... I use one of the light boxes exfo sells here on the forum... really well made and adjustable more info later.
Dark Flats ..... same length as Flats with cap on
Bias .... fastest exposure camera can do with cap on

Things Iíve found useful

If doing darks during the daylight hours check absolutely no light leaks get in, the tiniest amount will cause a problem
Flats , the light boxes are a treat, because some color filters have different responses, you can adjust the intensity to allow the same exposure for all filters, in my case as I have a shutter I use 3 seconds, and adjust the intensity to keep histogram in same place, Iím a big fan of keeping things as equal as possible this way I can use the same dark flats for all the filters.

DSS creators made it so all could be used, I do and donít have too many issues other than the odd cosmetic pixel getting through.
Reply With Quote
  #6  
Old 07-03-2021, 08:34 PM
Alchemy (Clive)
Quietly watching

Alchemy is offline
 
Join Date: Jul 2007
Location: Yarra Junction
Posts: 3,030
Make sure your flats are well into the histogram, so space at either end,
As with all these things consistency is the key, same temperature, gain, etc for everything, donít mix and match stuff,
CHECK THE FITS HEADER ON YOUR CALIBRATION FILES perhaps gain offset settings are different, some capture programs require you to set them each run (QHY does)

If youíre doing Tshirt Flats they will likely be different as you canít control the light well, if this is the case itís seperate dark flats for each filter, donít mix and match.

Try the Deepsky stacker program, itís free and Iíve never needed anything else.
Reply With Quote
  #7  
Old 07-03-2021, 08:36 PM
BlakPhoenix (Rohan)
Astro With RoRo

BlakPhoenix is offline
 
Join Date: Jan 2019
Location: Sydney
Posts: 17
Sorry all, I should have clarified.


This is using darks and flat darks too. The flats are 30 seconds long, flat darks are also 30 seconds. The light frames are 240 seconds and the darks are also 240 seconds. All images taken at -10C, 120 gain & 2x2 binning on the 249MM. The flats are taken using a flat pannel at night, so no t-shirt method or other.


This is all done in NINA, with the exact same settings between image types. I will try DSS and report back. Hoping it's just a weird setting in PIX.
Reply With Quote
  #8  
Old 07-03-2021, 08:59 PM
BlakPhoenix (Rohan)
Astro With RoRo

BlakPhoenix is offline
 
Join Date: Jan 2019
Location: Sydney
Posts: 17
Gave this a go in DSS and am seeing the same issue (see below image). I also took a screenshot of the histogram, I believe this is exposed correctly for a flat?
Attached Thumbnails
Click for full-size image (flat-histo.PNG)
13.1 KB20 views
Click for full-size image (dss-flat-test.jpg)
188.1 KB20 views
Reply With Quote
  #9  
Old 07-03-2021, 09:16 PM
multiweb's Avatar
multiweb (Marc)
ze frogginator

multiweb is offline
 
Join Date: Oct 2007
Location: Hinchinbrook
Posts: 20,656
Quote:
Originally Posted by BlakPhoenix View Post
Gave this a go in DSS and am seeing the same issue (see below image). I also took a screenshot of the histogram, I believe this is exposed correctly for a flat?
Could you please dropbox one light sub, your master flat + dark flat, dark (if any) and bias? Will have a look. (all FITS format)
Reply With Quote
  #10  
Old 08-03-2021, 08:17 AM
Alchemy (Clive)
Quietly watching

Alchemy is offline
 
Join Date: Jul 2007
Location: Yarra Junction
Posts: 3,030
Flat histogram all good.

Send stuff off for a second opinion always a good idea

The only other thing that comes to mind, is maybe it iced up sometime during the process and itís given you a false reading around the edges. Maybe you can run the camera for a while and check , reshoot the calibration then whiz a torch down the tube at the end.
Reply With Quote
  #11  
Old 08-03-2021, 09:37 AM
BlakPhoenix (Rohan)
Astro With RoRo

BlakPhoenix is offline
 
Join Date: Jan 2019
Location: Sydney
Posts: 17
Ok, I figured it out. I knew I had to be doing something wrong somewhere along the way. Turns out the darks / flat darks when I took the darks I had an older version of the camera's driver installed that defaulted to 0 offset, where as these new images used an updated driver that defaults to an offset of 8!


Thanks Alchemy for your suggestion to recheck all my calibration files. I looked into the headers of each and it was staring right at me!


Just goes to show that I need to check all my setting after every software change. I thought the issue was because of the new narrowband filters, but instead it was all software related!


Took some new darks/flat darks overnight and boom, perfectly calibrated frames!


Thanks to everyone for their help and big thank you to multiweb for your preparedness to even look into my fits/exifs.
Reply With Quote
  #12  
Old 08-03-2021, 05:11 PM
The_bluester's Avatar
The_bluester (Paul)
Registered User

The_bluester is offline
 
Join Date: Feb 2011
Location: Kilmore, Australia
Posts: 2,975
Assuming the 294MM behaves the same way as the 294MC, don't use bias frames. They don't behave as expected.

With my 294MC, I used lights and darks at matching temp, exposure, gain and offset, then for flats I used a dim light panel to get ten second exposure times for a good flat frame, and ten second dark-flats at matching temperature, gain and offset.

If you do not apply a master dark as well as the master flat, the dark current (Which is relatively even) will be accentuated in the corners where vignetting is being corrected by the master flat. Every time I use a flat/master flat on a light frame without a master dark I get something similar to what you posted in the first post.
Reply With Quote
Reply

Bookmarks

Thread Tools
Rate This Thread
Rate This Thread:

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off

Forum Jump


All times are GMT +10. The time is now 11:48 AM.

Powered by vBulletin Version 3.8.7 | Copyright ©2000 - 2021, Jelsoft Enterprises Ltd.
Advertisement
NexDome Observatories
Advertisement
Testar
Advertisement
Limpet Controller
Advertisement
Bintel
Advertisement
Astronomy and Electronics Centre
Advertisement