Jump to content

  •  

CNers have asked about a donation box for Cloudy Nights over the years, so here you go. Donation is not required by any means, so please enjoy your stay.

Photo

Vingetting and Flats

  • Please log in to reply
9 replies to this topic

#1 moorcoo

moorcoo

    Lift Off

  • -----
  • topic starter
  • Posts: 12
  • Joined: 05 Jul 2021
  • Loc: Sydney

Posted 02 August 2021 - 04:43 AM

Hey all,

 

I get this very pronounced vingetting occuring on my images. I was under the impression that flats were supposed to mitigate this.

 

So the attached image is about 500 30sec exposures taken by my unmodified canon 1100d. It has 60 darks, 100 flats, 100 dark flats, 100 bias.

 

Any help would be greatly appreciated smile.gif smile.gif

Attached Thumbnails

  • Capture-min.png

Edited by moorcoo, 02 August 2021 - 04:56 AM.


#2 pyrasanth

pyrasanth

    Aurora

  • *****
  • Posts: 4,606
  • Joined: 08 Jan 2016

Posted 02 August 2021 - 07:28 AM

Flats will only work if they have been produced correctly and participating in a calibration sequence.

 

Please can you provide details as to how you produced your flats and the settings you use to integrate the subs to produce the master calibration frames. It is clear from your image that your flats are not working at all or very badly.

 

There is a clearly defined process to produce calibration masters and in order to help we need to be sure that the procedure has been followed to correctly produce the masters.


Edited by pyrasanth, 02 August 2021 - 07:31 AM.


#3 Tapio

Tapio

    Aurora

  • -----
  • Posts: 4,706
  • Joined: 24 Sep 2006
  • Loc: Tampere, Finland

Posted 02 August 2021 - 09:22 AM

You only need dark flats or bias not both.



#4 moorcoo

moorcoo

    Lift Off

  • -----
  • topic starter
  • Posts: 12
  • Joined: 05 Jul 2021
  • Loc: Sydney

Posted 02 August 2021 - 06:39 PM

Flats will only work if they have been produced correctly and participating in a calibration sequence.

 

Please can you provide details as to how you produced your flats and the settings you use to integrate the subs to produce the master calibration frames. It is clear from your image that your flats are not working at all or very badly.

 

There is a clearly defined process to produce calibration masters and in order to help we need to be sure that the procedure has been followed to correctly produce the masters.

Hi pyrasanth,

 

My flats were produced seperate from the imaging session and were done py placing a white tshirt with an ipad ontop showing a plain white screen over my 72mm refractor. ISO 800 with the fastest shutter speed. Then added the images in to DSS.

 

Upon doing some more research, I think from memory that the histogram for my flats was not dead centre and was slightly more towards the left, could this be the issue?

 

Thanks,



#5 pedxing

pedxing

    Vanguard

  • *****
  • Posts: 2,483
  • Joined: 03 Nov 2009
  • Loc: SE Alaska

Posted 02 August 2021 - 07:06 PM

If you are using both dark flats and bias, you are effectively subtracting the bias twice.

 

As Tapio said, use one or the other, not both.



#6 moorcoo

moorcoo

    Lift Off

  • -----
  • topic starter
  • Posts: 12
  • Joined: 05 Jul 2021
  • Loc: Sydney

Posted 02 August 2021 - 07:52 PM

Right okay, that makes sense! Thank you all. I will restack again and see if flats, darks and biases get rid of that vingetting (no dark flats).



#7 moorcoo

moorcoo

    Lift Off

  • -----
  • topic starter
  • Posts: 12
  • Joined: 05 Jul 2021
  • Loc: Sydney

Posted 03 August 2021 - 12:55 AM

So I tried using just flats without dark flats and still got the same result. Huge vingetting. Any other suggestions?



#8 bobzeq25

bobzeq25

    ISS

  • *****
  • Posts: 25,667
  • Joined: 27 Oct 2014

Posted 03 August 2021 - 01:11 AM

So I tried using just flats without dark flats and still got the same result. Huge vingetting. Any other suggestions?

I can tell you what it's not.  The histogram.  You just need to be away from the edges.

 

Beginners often have this problem.  By far the most common cause is doing something wrong when calibrating the images in the software.  Not in taking the flats.  Unless you've changed the orientation of the camera re the scope.  Disassembling the setup, and reassembling, does not work.

 

So, you're using DSS?  What's your workflow?  Are you changing the defaults?

 

It's possible (but unlikely) to cause vignetting so severe that flats can't fix it.  You could, for example, put a 1.25 inch tube somewhere in the optical path.  Could you post two pictures of the setup?  One of the whole thing, one that shows the specific area between the end of the scope and the camera.  Or upload a light, straight from the camera, to something like Dropbox, post the link, and ask that someone looks at it.


Edited by bobzeq25, 03 August 2021 - 01:27 AM.


#9 moorcoo

moorcoo

    Lift Off

  • -----
  • topic starter
  • Posts: 12
  • Joined: 05 Jul 2021
  • Loc: Sydney

Posted 03 August 2021 - 05:42 PM

Hi Bobzeq,

Yeah, I'm using DSS. Work flow is pretty straightforward. Add calibration frames in by clicking on their respective link to add the images. Hit register. Apply the recommended settings and then let it do it's thing.

I strongly doubt it has anything to do with my physical setup as I know people using an identical setup to mine who don't experience the vingetting.

Thanks,

#10 moorcoo

moorcoo

    Lift Off

  • -----
  • topic starter
  • Posts: 12
  • Joined: 05 Jul 2021
  • Loc: Sydney

Posted 03 August 2021 - 05:42 PM

Hi Bobzeq,

Yeah, I'm using DSS. Work flow is pretty straightforward. Add calibration frames in by clicking on their respective link to add the images. Hit register. Apply the recommended settings and then let it do it's thing.

I strongly doubt it has anything to do with my physical setup as I know people using an identical setup to mine who don't experience the vingetting.

Thanks,


CNers have asked about a donation box for Cloudy Nights over the years, so here you go. Donation is not required by any means, so please enjoy your stay.


Recent Topics






Cloudy Nights LLC
Cloudy Nights Sponsor: Astronomics