#1  
Old 15-06-2012, 06:29 PM
multiweb's Avatar
multiweb (Marc)
ze frogginator

multiweb is offline
 
Join Date: Oct 2007
Location: Hinchinbrook
Posts: 18,138
Flats for solar imaging

Recently I became aware of how important flat fielding dust bunnies is for solar imaging. What's the proper way to do it? Slightly defocus, or offset the sun or any kind of translucent shield in front? I'd be interested to hear what the common practice is out there? TIA.
Reply With Quote
  #2  
Old 16-06-2012, 02:06 PM
alocky's Avatar
alocky (Andrew lockwood)
PI popular people's front

alocky is offline
 
Join Date: Aug 2010
Location: perth australia
Posts: 1,287
I centre the scope on the brightest part of the solar disc, being careful to avoid any active regions and sunspots, then defocus enough for it to be featureless. So far this seems to eliminate dust spots, newtons rings and gradients.
Cheers,
Andrew.
Reply With Quote
  #3  
Old 16-06-2012, 04:53 PM
Merlin66's Avatar
Merlin66 (Ken)
Spectroscopy Wizard

Merlin66 is offline
 
Join Date: Oct 2005
Location: St Leonards, Vic
Posts: 6,966
There's a lot of info and discussion on taking and the application of solar flats over on the new Solar Chat forum.
Well worth checking out.
http://solarchat.solarastronomy.org/index.php/en/
Reply With Quote
  #4  
Old 16-06-2012, 05:16 PM
multiweb's Avatar
multiweb (Marc)
ze frogginator

multiweb is offline
 
Join Date: Oct 2007
Location: Hinchinbrook
Posts: 18,138
Thanks fo the links and tips guys. Here's a post that made sense to me and that I will try tomorrow. See below for the benefits of others.

1) after capturing a sequence or a series of sequences, without changing the camera orientation and, if it's the case, without changing ROI (frame size), move the scope to a featurless area and then defocus until you have a rather ... featurless picture on video. Then take a sequence of say 200-300 frames.
2) Take a new such sequence every time you change the camera orientation or frame size.
3) When you go about processing the sequences captured create a flat field frame using the software you normally use (I use avistack and that program has a feature that automatically creates flats from a given sequence).
4) in avistack in the processing parameters there's a "frame stacking" section. If you open that section by clicking on it, you'll find the flat field and dark frame area. double click on the flat field and there you'll find a menu that allows you to choose the appropriate flat for the sequence you are about to process. Select the flat field frame you just created or the appropriate one for that sequence or series of sequences and then let avistack do its thing.
Reply With Quote
  #5  
Old 16-06-2012, 05:57 PM
alocky's Avatar
alocky (Andrew lockwood)
PI popular people's front

alocky is offline
 
Join Date: Aug 2010
Location: perth australia
Posts: 1,287
I take a minute's worth of video at the end of every mosaic run, and put the lens cap on to do another minute of dark. Thanks to some of the guys here I've switched to Autostakkert from Avistack, which also lets you create a dark and a flat file, which you load into the code before processing the image runs and it manages it pretty much automatically.
I've got a couple of solar mosaics using this technique at
http://astrobin.com/users/alocky/
Including a venus transit one.
cheers,
Andrew

Last edited by alocky; 16-06-2012 at 05:58 PM. Reason: typos
Reply With Quote
  #6  
Old 17-06-2012, 07:42 PM
multiweb's Avatar
multiweb (Marc)
ze frogginator

multiweb is offline
 
Join Date: Oct 2007
Location: Hinchinbrook
Posts: 18,138
Quote:
Originally Posted by alocky View Post
I take a minute's worth of video at the end of every mosaic run, and put the lens cap on to do another minute of dark. Thanks to some of the guys here I've switched to Autostakkert from Avistack, which also lets you create a dark and a flat file, which you load into the code before processing the image runs and it manages it pretty much automatically.
I've got a couple of solar mosaics using this technique at
http://astrobin.com/users/alocky/
Including a venus transit one.
cheers,
Andrew
Thanks Andrew. I downloaded Autostakkert. Pretty easy to use. It doesn't have the wavelet section that registar and avistack have though unless I'm missing something.
Reply With Quote
  #7  
Old 17-06-2012, 07:53 PM
jjjnettie's Avatar
jjjnettie (Jeanette)
Registered User

jjjnettie is offline
 
Join Date: Feb 2005
Location: Far Far Away
Posts: 16,726
You have to save your file and reopen it in Registax and then do your wavelets.
Reply With Quote
  #8  
Old 17-06-2012, 07:53 PM
multiweb's Avatar
multiweb (Marc)
ze frogginator

multiweb is offline
 
Join Date: Oct 2007
Location: Hinchinbrook
Posts: 18,138
Test processed in 3 separate softwares

This AVI sequence was taken with a DMK21AF04 at 30fps at 600mm FL 90mm refractor, white light and YUV codec, approx 1000 frame. Might have done something wrong there as it's a mono. but I don't recall IC capture giving me any other option for the capture format.

The image size is 640x480px. I also wonder if the low resoltution contributed to the lines and blockiness when I ran registar wavelets on the stacked final picture (1st shot).

The second shot is the stack out of Avistack2.

The thrid shot is Autostakkert.

The 4th is the Autostakkert stack sharpened in PixInsight.

DO you know what caused the lines with Registax? Am I doing something wrong during data acquisition? Is it undersampled?
Attached Thumbnails
Click for full-size image (registax_wvlt.jpg)
126.1 KB27 views
Click for full-size image (AviStack2.jpg)
44.0 KB24 views
Click for full-size image (Autostakkert.jpg)
46.0 KB26 views
Click for full-size image (Autostakkert_PI.jpg)
70.1 KB22 views
Reply With Quote
  #9  
Old 17-06-2012, 07:55 PM
multiweb's Avatar
multiweb (Marc)
ze frogginator

multiweb is offline
 
Join Date: Oct 2007
Location: Hinchinbrook
Posts: 18,138
Quote:
Originally Posted by jjjnettie View Post
You have to save your file and reopen it in Registax and then do your wavelets.
Ha... I'm not sure how to do that. Open a single frame and apply wavelet only.
Reply With Quote
  #10  
Old 17-06-2012, 08:58 PM
jjjnettie's Avatar
jjjnettie (Jeanette)
Registered User

jjjnettie is offline
 
Join Date: Feb 2005
Location: Far Far Away
Posts: 16,726
If you save your stacked image as a tif, just open it in registax and it will take you straight to the wavelets.
Reply With Quote
  #11  
Old 18-06-2012, 04:42 AM
multiweb's Avatar
multiweb (Marc)
ze frogginator

multiweb is offline
 
Join Date: Oct 2007
Location: Hinchinbrook
Posts: 18,138
Quote:
Originally Posted by jjjnettie View Post
If you save your stacked image as a tif, just open it in registax and it will take you straight to the wavelets.
Cool - will try that.
Reply With Quote
  #12  
Old 18-06-2012, 11:37 AM
multiweb's Avatar
multiweb (Marc)
ze frogginator

multiweb is offline
 
Join Date: Oct 2007
Location: Hinchinbrook
Posts: 18,138
Found the wavelet for TIFFs in registax. Works quite well.

I also checked the codec I used with IC capture and although I used Y800 for the acquisition I used another one for saving the AVI and somehow ended up making a color video (out of the mono cam) so it must have halved the res and stuck a bayer pattern in there which is what popped its ugly head when sharpening. I did another test this morning with the right codec and all is well. Much better. Pfeewh... for a sec I thought the DMK21 would be too low res to do decent solar imaging.
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 02:24 PM.

Powered by vBulletin Version 3.8.7 | Copyright ©2000 - 2019, Jelsoft Enterprises Ltd.
Advertisement
Lunatico Astronomical
Advertisement
Bintel
Advertisement
Meade Australia
Advertisement
NexDome Observatories
Advertisement
Celestron Australia
Advertisement
SkyWatcher Australia
Advertisement
OzScopes Authorised Dealer
Advertisement
Astronomy and Electronics Centre
Advertisement