Flats from near full disk?
- MAURITS
- Way More Fun to Share It!!
- Posts: 8507
- Joined: Tue Nov 27, 2018 4:37 pm
- Location: Belgium
- Has thanked: 2412 times
- Been thanked: 4786 times
- Contact:
Flats from near full disk?
How do you take flats from a near full disk?
When I do this with my 150mm scope with the Quark / IMX174 combination, then I go to the surface of the sun where I can't see the edge (defocus), I take a flat and load it in AutoStakkert.
So no big deal ... so far all good.
Now I have a little 60mm scope and with the same Quark / IMX174 combination I have near full disk (except a part above and a part below).
So I always see the near full disk AND the edge when I take a (defocused) flat with the little scope.
When I go to AutoStakkert, than I see strange things outside the disk if I load the masterflat.
How can I solve this problem?
This is my FLAT.
Next is a "unprocessed" image from my 60mm scope (and the above combination) done in AutoStakkert WITHOUT flatframe.
This is a result from AutoStakkert WITH flatframe.
All the black color outside the sun is gone ...???
What happend on the edge?
When I do this with my 150mm scope with the Quark / IMX174 combination, then I go to the surface of the sun where I can't see the edge (defocus), I take a flat and load it in AutoStakkert.
So no big deal ... so far all good.
Now I have a little 60mm scope and with the same Quark / IMX174 combination I have near full disk (except a part above and a part below).
So I always see the near full disk AND the edge when I take a (defocused) flat with the little scope.
When I go to AutoStakkert, than I see strange things outside the disk if I load the masterflat.
How can I solve this problem?
This is my FLAT.
Next is a "unprocessed" image from my 60mm scope (and the above combination) done in AutoStakkert WITHOUT flatframe.
This is a result from AutoStakkert WITH flatframe.
All the black color outside the sun is gone ...???
What happend on the edge?
- marktownley
- Librarian
- Posts: 42269
- Joined: Tue Oct 18, 2011 5:27 pm
- Location: Brierley Hills, UK
- Has thanked: 20424 times
- Been thanked: 10243 times
- Contact:
Re: Flats from near full disk?
The unfocused flat is bigger on the chip than the focused image, so when the flat is applied its affects go beyond the limb of the sun.
http://brierleyhillsolar.blogspot.co.uk/
Solar images, a collection of all the most up to date live solar data on the web, imaging & processing tutorials - please take a look!
- MAURITS
- Way More Fun to Share It!!
- Posts: 8507
- Joined: Tue Nov 27, 2018 4:37 pm
- Location: Belgium
- Has thanked: 2412 times
- Been thanked: 4786 times
- Contact:
- marktownley
- Librarian
- Posts: 42269
- Joined: Tue Oct 18, 2011 5:27 pm
- Location: Brierley Hills, UK
- Has thanked: 20424 times
- Been thanked: 10243 times
- Contact:
Re: Flats from near full disk?
I'm not sure you can effectively, the full disk flat is a holy grail for solar!
http://brierleyhillsolar.blogspot.co.uk/
Solar images, a collection of all the most up to date live solar data on the web, imaging & processing tutorials - please take a look!
- PDB
- Almost There...
- Posts: 702
- Joined: Mon Aug 15, 2016 4:23 pm
- Location: Belgium
- Has thanked: 2 times
- Been thanked: 149 times
Re: Flats from near full disk?
The holy grail indeed ...
I am surprised it even worked good, except for the solar edges. There is also some limb darkening effect that will "ruin" the flats (but maybe it helps to remove the gradient towards the limb?)
Now I would try either one of the following:
- Take the flats with the plastic bag in front without defocusing (probably will not really work)
- in PS or Gimp or whatever try to reduce the flats size by a small amount so the disc size is the same as on the sun image. This might be a tricky job, because:
1. the flats total size should remain the same to be applied in AS!3 (so only disc should be smaller)
2. the image of the Sun on the video for stacking should not move (and in same place as on the flat) or the applied flat will again make it worse.
Looks a bit impossible, but you neve know ....
Regards,
Paul
PS: The gradients you can probably remove with an artificial flat, but for the dust motes only cleaning helps. But these always seem to come back. (Even seconds after cleaning)
I am surprised it even worked good, except for the solar edges. There is also some limb darkening effect that will "ruin" the flats (but maybe it helps to remove the gradient towards the limb?)
Now I would try either one of the following:
- Take the flats with the plastic bag in front without defocusing (probably will not really work)
- in PS or Gimp or whatever try to reduce the flats size by a small amount so the disc size is the same as on the sun image. This might be a tricky job, because:
1. the flats total size should remain the same to be applied in AS!3 (so only disc should be smaller)
2. the image of the Sun on the video for stacking should not move (and in same place as on the flat) or the applied flat will again make it worse.
Looks a bit impossible, but you neve know ....
Regards,
Paul
PS: The gradients you can probably remove with an artificial flat, but for the dust motes only cleaning helps. But these always seem to come back. (Even seconds after cleaning)
- Montana
- Librarian
- Posts: 34559
- Joined: Mon Oct 17, 2011 5:25 pm
- Location: Cheshire, UK
- Has thanked: 17666 times
- Been thanked: 8787 times
Re: Flats from near full disk?
It is impossible if you have black edges. I always recommend the drift method. Let the image slowly drift a bit in capture and ASK3 will reduce all the dust bunnies away.
Try to clean the camera as best as you can
Alexandra
Try to clean the camera as best as you can
Alexandra
- MAURITS
- Way More Fun to Share It!!
- Posts: 8507
- Joined: Tue Nov 27, 2018 4:37 pm
- Location: Belgium
- Has thanked: 2412 times
- Been thanked: 4786 times
- Contact:
Re: Flats from near full disk?
I try to take a FD capture with a cleaner sensor and without flat frames.
Thanks all for the info.
Thanks all for the info.
- marktownley
- Librarian
- Posts: 42269
- Joined: Tue Oct 18, 2011 5:27 pm
- Location: Brierley Hills, UK
- Has thanked: 20424 times
- Been thanked: 10243 times
- Contact:
Re: Flats from near full disk?
Give it a go Maurits but I don't think you will get rid of the uneven illumination due to variation in bandpass across that quarks FOV, the variation in bandpass will always give a variation in detail. Doubt you will stitch images together for this reason (to get a full disk). My advice if you're after a full disk is get one of the dedicated 40-60mm solar scopes.
http://brierleyhillsolar.blogspot.co.uk/
Solar images, a collection of all the most up to date live solar data on the web, imaging & processing tutorials - please take a look!
- MAURITS
- Way More Fun to Share It!!
- Posts: 8507
- Joined: Tue Nov 27, 2018 4:37 pm
- Location: Belgium
- Has thanked: 2412 times
- Been thanked: 4786 times
- Contact:
Re: Flats from near full disk?
Well Mark, I have a very little Lunt LS 35THA scope, I give it a try with these if it will work with my ZWO 174MM camera.
- marktownley
- Librarian
- Posts: 42269
- Joined: Tue Oct 18, 2011 5:27 pm
- Location: Brierley Hills, UK
- Has thanked: 20424 times
- Been thanked: 10243 times
- Contact:
Re: Flats from near full disk?
I think you will get better results with a camera with smaller pixels, the IMX174 sensor is best suited up at around f25 in Ha.
http://brierleyhillsolar.blogspot.co.uk/
Solar images, a collection of all the most up to date live solar data on the web, imaging & processing tutorials - please take a look!
- MAURITS
- Way More Fun to Share It!!
- Posts: 8507
- Joined: Tue Nov 27, 2018 4:37 pm
- Location: Belgium
- Has thanked: 2412 times
- Been thanked: 4786 times
- Contact:
-
- Im an EXPERT!
- Posts: 385
- Joined: Sun Oct 29, 2017 9:51 pm
- Has thanked: 286 times
- Been thanked: 399 times
Re: Flats from near full disk?
Hi Maurits
Hope you don't mind but I had a play with your image above as I am interested in the same thing, removing variations in brightness.
It sort of works but as Mark says you can't remove the bandpass variations.
What I did was copy your image, then I saved two copies.
One copy I used gaussian blur in PS6cs set at 9.8 to make a flat.
then loaded the suns image into AutoStakkert and then the new flat, then saved the image.
I then increased the new images size by about 2.5% in PS6cs and cut out the suns image with edge blur set at 10 and layed it over the original suns image.
I then just used RegiStax wavelets to bring out a little detail to see how the bandpass zones are.
Not perfect but some way towards getting a flatter image.
I had two or three goes trying different parameters, the hardest part is selecting the solar disk for cropping.
Just an idea cheers Rod
Hope you don't mind but I had a play with your image above as I am interested in the same thing, removing variations in brightness.
It sort of works but as Mark says you can't remove the bandpass variations.
What I did was copy your image, then I saved two copies.
One copy I used gaussian blur in PS6cs set at 9.8 to make a flat.
then loaded the suns image into AutoStakkert and then the new flat, then saved the image.
I then increased the new images size by about 2.5% in PS6cs and cut out the suns image with edge blur set at 10 and layed it over the original suns image.
I then just used RegiStax wavelets to bring out a little detail to see how the bandpass zones are.
Not perfect but some way towards getting a flatter image.
I had two or three goes trying different parameters, the hardest part is selecting the solar disk for cropping.
Just an idea cheers Rod
- Attachments
-
[The extension tif has been deactivated and can no longer be displayed.]
- marktownley
- Librarian
- Posts: 42269
- Joined: Tue Oct 18, 2011 5:27 pm
- Location: Brierley Hills, UK
- Has thanked: 20424 times
- Been thanked: 10243 times
- Contact:
Re: Flats from near full disk?
Yup, I thunk that is the best you will get with that method Rod, good result.
http://brierleyhillsolar.blogspot.co.uk/
Solar images, a collection of all the most up to date live solar data on the web, imaging & processing tutorials - please take a look!
-
- Im an EXPERT!
- Posts: 385
- Joined: Sun Oct 29, 2017 9:51 pm
- Has thanked: 286 times
- Been thanked: 399 times
Re: Flats from near full disk?
Hi I had another play with the image.
Shadows and highlights and added colour.
Not to bad, maybe a little over processed in places but does show some even detail.
Shadows and highlights and added colour.
Not to bad, maybe a little over processed in places but does show some even detail.
- Attachments
-
- Mautris Colour flat.jpg (491.58 KiB) Viewed 2403 times
- Valery
- Way More Fun to Share It!!
- Posts: 4059
- Joined: Sun Nov 18, 2012 3:13 pm
- Has thanked: 156 times
- Been thanked: 893 times
Re: Flats from near full disk?
The only method which is correct and which will help is: place a white cloth or white piece of paper in front of the objective and record a flat field movie with about 60% histogram fill. One will need to increase the exposure and slightly increase the gain to fill the histogram. If it will be too noisy use more frames (about 500 frames movie) to stack for FF.
This FF movie must be recorded when a telescope was focused and pointed at the center of the sun.
Gamma setting must be the same for the focused images and for the FF.
Valery
This FF movie must be recorded when a telescope was focused and pointed at the center of the sun.
Gamma setting must be the same for the focused images and for the FF.
Valery
"Solar H alpha activity is the most dynamic and compelling thing you can see in a telescope, so spend accordingly." (c) Bob Yoesle.
Largest full size 185 - 356mm Dielectric Energy Rejection Filters (D-ERF) by ARIES Instruments.
Largest full size 185 - 356mm Dielectric Energy Rejection Filters (D-ERF) by ARIES Instruments.
- MAURITS
- Way More Fun to Share It!!
- Posts: 8507
- Joined: Tue Nov 27, 2018 4:37 pm
- Location: Belgium
- Has thanked: 2412 times
- Been thanked: 4786 times
- Contact:
Re: Flats from near full disk?
Yes Rod, this is a lot better than before.
With the added color even more better ...
This is a very nice explanation Rod.
A thank you for Mark, Paul, Alexandra, Rod and Valery.
With the added color even more better ...
This is a very nice explanation Rod.
A thank you for Mark, Paul, Alexandra, Rod and Valery.
-
- Im an EXPERT!
- Posts: 385
- Joined: Sun Oct 29, 2017 9:51 pm
- Has thanked: 286 times
- Been thanked: 399 times
Re: Flats from near full disk?
Hi Maurits
Yep the second image shows the info is all there and easy to bring out once it has been flattened.
I will be up for trying Valery's method when I get my full disk setup it does sound good.
One tip I use for deep sky flats is a white drum skin over the objective pointed at the sky or a light source.
They come in all sizes, are cheap, easy to get and very durable.
With the lip they are also easy to put on and off without moving the scope when pointed at the sun.
Cheers Rod
Yep the second image shows the info is all there and easy to bring out once it has been flattened.
I will be up for trying Valery's method when I get my full disk setup it does sound good.
One tip I use for deep sky flats is a white drum skin over the objective pointed at the sky or a light source.
They come in all sizes, are cheap, easy to get and very durable.
With the lip they are also easy to put on and off without moving the scope when pointed at the sun.
Cheers Rod
- MAURITS
- Way More Fun to Share It!!
- Posts: 8507
- Joined: Tue Nov 27, 2018 4:37 pm
- Location: Belgium
- Has thanked: 2412 times
- Been thanked: 4786 times
- Contact: