Flats problem

Use this section to discuss "standard" Baader/Coronado/ Lunt SolarView/ Daystar, etc… filters, cameras and scopes. No mods, just questions/ answers and reviews.
Post Reply
Seachronicity
The Sun?
The Sun?
Posts: 7
Joined: Mon Jan 26, 2015 6:39 pm

Flats problem

Post by Seachronicity » Sun May 17, 2015 6:29 pm

I'm new to solar imaging and I'm having trouble with flats and Astrostakkert. I either defocus or use a bag and create a Master Flat. When I load it, the image is not aligned with the flat due to a slight drift.

Other than correcting the tracking, is there another way to align the flat with the image?

Thanks

Barry

User avatar
grimble_cornet
Way More Fun to Share It!!
Way More Fun to Share It!!
Posts: 3493
Joined: Tue Jul 10, 2012 5:10 pm
Location: UK West Midlands

Re: Flats problem

Post by grimble_cornet » Sun May 17, 2015 8:46 pm

Hi Barry and welcome to the wonderful world of solar imaging.

I don't understand what you mean by 'slight drift' and don't see any need to even consider 'tracking' or 'aligning'.
As long as you take the flat without changing the focus or rotating the camera then it will automatically 'align' with your light images.
Obviously, if you add/remove Barlows, Focal reducers or filters.......or rotate the camera....... you will need to take a new flat to match the new set up.

If I can fill the field of view with the sun then I simply focus, stretch a piece of clingfilm over the dew-shield, increase exposure slightly to compensate (use the histogram) and capture about 100 frames. The avi/ser file is then loaded into Autostakkert and a 'masterframe' created. I then load the FLAT (masterframe saved as FLAT) and load and process the capture files - perfect results every time.

If I can't fill the field with the sun then I use a plastic bag which will diffuse the image. This will need considerably more expose to give 60-80% on the histogram (in FireCapture) but otherwise works in exactly the same way as the clingfilm version.

The key points are:
Don't change anything in the optical path (focus, Barlow, Filter, camera position etc.) between taking the flat and the normal captures.
Capture about 100 frames for your flat with exposure roughly the same as you use for your normal captures (check the histogram).
If you change anything (focus, Barlow, Filter, camera position etc.) then take another flat to use with the new set-up.

I assume that you are capturing videos (avi or ser files) - if you are using a still camera then the above still applies but take several still frames and stack to produce the flat.

Good luck, look forward to seeing your results.
.

.



.


Mike Garbett

Selection of Solar and Deep Sky images on Flickr: https://www.flickr.com/photos/mikegarbett/

Seachronicity
The Sun?
The Sun?
Posts: 7
Joined: Mon Jan 26, 2015 6:39 pm

Re: Flats problem

Post by Seachronicity » Sun May 17, 2015 11:12 pm

Thanks, Mike. I appreciate your suggestions.

I'm taking AVIs. I'm not changing anything, but the sun does drift slightly in the camera field between imaging runs. If you superimpose a flat over an object that has moved slightly, an edge becomes improperly illuminated.

Seachronicity
The Sun?
The Sun?
Posts: 7
Joined: Mon Jan 26, 2015 6:39 pm

Re: Flats problem

Post by Seachronicity » Sun May 17, 2015 11:16 pm

I forgot to mention that this occurs when I'm taking a full disc image
Barry

User avatar
grimble_cornet
Way More Fun to Share It!!
Way More Fun to Share It!!
Posts: 3493
Joined: Tue Jul 10, 2012 5:10 pm
Location: UK West Midlands

Re: Flats problem

Post by grimble_cornet » Sun May 17, 2015 11:32 pm

Ah, that makes sense........... in which case you need to diffuse the image more to lose the edges.
I would explore using different types of plastic bag. Not sure where you are, but in the UK the bags used by supermarkets for fruit and vegetables work quite well. If the plastic is too thick or opaque, you will need very long exposures.................... its a matter of trying out different materials and seeing what works.
Most people say that de-focusing is a bad idea and I would normally agree BUT................. I have had some success in the past with combining a plastic bag over the scope and some defocusing to get a fairly even result.
The danger with using flats is that if you get it wrong, you can ADD problems rather than take them away. Unless I have problems with 'dust bunnies' I often don't even bother with flats when shooting FDs. They become really important when you are capturing images which you intend to combine as a mosaic. Fortunately it is then easy to fill the field of view with a fairly 'bland' part of the disc to create the perfect flat.
.

.



.


Mike Garbett

Selection of Solar and Deep Sky images on Flickr: https://www.flickr.com/photos/mikegarbett/

Seachronicity
The Sun?
The Sun?
Posts: 7
Joined: Mon Jan 26, 2015 6:39 pm

Re: Flats problem

Post by Seachronicity » Sun May 17, 2015 11:54 pm

Thank you Mike. Checked your site... Phenomenal images!

User avatar
nickatnight
Almost There...
Almost There...
Posts: 638
Joined: Sat May 30, 2015 5:30 am
Location: Santa Clarita, California

Re: Flats problem

Post by nickatnight » Sat May 30, 2015 7:25 am

I'm very new to solar imaging and solar flats, but had success today. I have drift too, as I'm imaging off a locked down tripod. I found with the right plastic and a bit of defocus, the solar disk itself is no longer "part" of the flat, and if I wiggle the scope around, I see no major change in the flats illumination. Then I do the flat capture.

Derek Klepp
Way More Fun to Share It!!
Way More Fun to Share It!!
Posts: 12383
Joined: Wed Oct 19, 2011 10:02 am

Re: Flats problem

Post by Derek Klepp » Sat May 30, 2015 9:46 am

The best advice I can give is take the flat directly after the Avi for best results if your mount is off .

Post Reply

Who is online

Users browsing this forum: No registered users and 2 guests