Can I improve my problematic DS images in post-processing?

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Can I improve my problematic DS images in post-processing?

Post by H-Alpha »

Hi all,

My disappointment by the DS of my Lunt130MT was the reason I stopped for quite some time to make solar photography. Although many of you with deep knowledge on H-alpha kindly tried to help, I realized that I could never use it successfully. Lunt was not answering anyway, so I was desperate feeling that I lost the money paid, but above all I lost the happiness I had with my SS.

The problem was (and still is of course) that I could never tune the DS in a large part of my field, and worst is that the tuned sweetspot is not homogeneous at all and neither circular. I think that the following two images show what I try to say. With these images I realized that the problem is probably in my original etalon and not the DS I bought later. I think to see that the problem exist in the SS image (left) and simply gets heavily accentuated when I pass to DS. Do you also think that this is the case?
SS-DS H-alph inhomogeneity.jpg
SS-DS H-alph inhomogeneity.jpg (736.77 KiB) Viewed 756 times
Anyway, this likely cannot change. My question is if you think there is any possible way to achieve a bit more pleasant and homogeneously lighten photos in post-processing. In other words, if I could automatically make the darker areas lighter or the opposite.

Any other comment is very welcome.

Best wishes,
Alexandros


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Re: Can I improve my problematic DS images in post-processing?

Post by rigel123 »

For that level of cost I would expect a lot more out of my scope. The SS doesn’t look too bad, but again, I would expect more from it than what I see in that image. The DS image looks like the contrast is even worse. Never having dealt with PT etalons I really don’t feel qualified to give suggestions other than I might try the DS unit as the primary and see how that performs, and then try the original primary etalon as the DS.


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Re: Can I improve my problematic DS images in post-processing?

Post by marktownley »

Hi ALexandros.

The Lunt130 is not designed for full disk photography. The sweet spot is smaller than a full disk, so tuning will never give an evenly tuned disk. The tighter bandpass of double stacking will just accentuate it more, which is what your images show. The scope is designed for hi-res images where the field of view is smaller than the sweetspot.

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Re: Can I improve my problematic DS images in post-processing?

Post by rigel123 »

marktownley wrote: Sun May 26, 2024 6:11 am Hi ALexandros.

The Lunt130 is not designed for full disk photography. The sweet spot is smaller than a full disk, so tuning will never give an evenly tuned disk. The tighter bandpass of double stacking will just accentuate it more, which is what your images show. The scope is designed for hi-res images where the field of view is smaller than the sweetspot.

Mark
That explains why the closeups I have seen Alexandros post look great. The full disk shots really had me stumped!


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Re: Can I improve my problematic DS images in post-processing?

Post by Bob Yoesle »

The same issue occurred with the LS152 when it was introduced. Larger aperture for it was intended for hi-res work, not full-disc where a smaller etalon system is more than adequate. Placing relatively small etalons in collimator systems usually requires a smaller FL collimator lens, which will increase field angle magnification and decrease the diameter of the Jacquinot ("sweet") spot.

For the best full disc viewing and imaging - which is the most difficult for commercial etalon systems - you generally need a pair of front mounted smaller etalons with good uniformity and CWLs close to being on-band with little tilt so as to avoid banding. That too sometimes seems a tall order these days.
The sweet spot is smaller than a full disk, so tuning will never give an evenly tuned disk. The tighter bandpass of double stacking will just accentuate it more, which is what your images show.
Ditto to what Mark stated. Any time you reduce the FWHM of an etalon, any non-uniformity is made more evident.

Even though the 130 isn't designed or ideal for the full disc purpose, the blotchy asymmetrical non-uniformity of the etalon(s) is unexpected. I would have thought it would be a more symmetrical form of sub-solar diameter circular sweet spot.

However, you also look to be off-band with both images.
My question is if you think there is any possible way to achieve a bit more pleasant and homogeneously lighten photos in post-processing. In other words, if I could automatically make the darker areas lighter or the opposite.
You can use flats to even out the brightness, but if you have significant non-uniformity originating with varying band-pass variation, the equalized brightness does not fix this root cause, and even though flats result in more even brightness, the bandpass variation in detail will still be present.

Be sure to let the etalon(s) thermally stabilize before reaching any conclusions. Since internal etalons are a bit more insulated via the collimating lens module and trapped air, it may take them longer to stabilize than the traditional air-spaced etalon on the front of the telescope.

As you surmised, it does look like the asymmetrical appearance originates with the primary etalon. I would be contacting the dealer where you purchased the telescope if this cannot be ameliorated with better etalon tuning and allowing for thermal stabilization.

Bob


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Re: Can I improve my problematic DS images in post-processing?

Post by H-Alpha »

Dear Warren, Mark,Bob, thanks a lot for your comments!

rigel123 wrote: Sun May 26, 2024 2:36 am Never having dealt with PT etalons I really don’t feel qualified to give suggestions other than I might try the DS unit as the primary and see how that performs, and then try the original primary etalon as the DS.
When I bought it, I also thought I would have that possibility, BUT unfortunately, Lunt have the DERF attached in a permanent way on the primary etalon... I cannot safely remove it, and even if I could, I would not be able to attache it to the DS etalon. :-( The DERF is internal, atached to the fronal side (of course) of the primary etalon.

Bob Yoesle wrote: Sun May 26, 2024 2:36 pm For the best full disc viewing and imaging - which is the most difficult for commercial etalon systems - you generally need a pair of front mounted smaller etalons with good uniformity and CWLs close to being on-band with little tilt so as to avoid banding. That too sometimes seems a tall order these days.
Bob, your comments, both theoretical and practical, are always precious!
What would you suggest as a reasonably priced DS solution for FDs?
If I could find a way to adapt my current Lunt etalons in a smaller scope, I would still have the problem since I don't have a central sweetspot. Isn't it?
Bob Yoesle wrote: Sun May 26, 2024 2:36 pm
the blotchy asymmetrical non-uniformity of the etalon(s) is unexpected. I would have thought it would be a more symmetrical form of sub-solar diameter circular sweet spot.
This is what disappointed me the most... (together with the lack of communication by Lunt when the warranty was still valid)

Bob Yoesle wrote: Sun May 26, 2024 2:36 pm However, you also look to be off-band with both images.
This is true, but what I wanted to show is the assymetry.


Bob Yoesle wrote: Sun May 26, 2024 2:36 pm You can use flats to even out the brightness, but if you have significant non-uniformity originating with varying band-pass variation, the equalized brightness does not fix this root cause, and even though flats result in more even brightness, the bandpass variation in detail will still be present.
This is a very good idea! I will try it, even though the bandpass varation will be present as you wrote.
Bob Yoesle wrote: Sun May 26, 2024 2:36 pm Be sure to let the etalon(s) thermally stabilize before reaching any conclusions. Since internal etalons are a bit more insulated via the collimating lens module and trapped air, it may take them longer to stabilize than the traditional air-spaced etalon on the front of the telescope.
I will follow your advise. How much time would seem good enough for such insulated etalons as in the internal Lunt ones? One hour or perhaps even more?

Thank you all once more.

Best wishes,
Alexandros


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Re: Can I improve my problematic DS images in post-processing?

Post by Bob Yoesle »

Hi Alexandros,

For double stacked front etalons I'd consider Solarscope 50, 60, or 70 etalons, or Lunt 60 or 100 etalons.

If you used the etalon(s) properly located with an objective with the same f ratio and a smaller focal length and objective diameter than the 130 you'd have a larger Jacquinot spot. But if they have the contrast irregularity form etalon plates that are uneven this issue will likely remain.

I would think that once you've pointed the telescope at the sun 15-20 minutes should be enough time for the etalons to stabilize. This might vary depending on the ambient temperature and other factors. Careful observation will reveal when they are stabilized and don't change much after the initial time period.

Bob


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Re: Can I improve my problematic DS images in post-processing?

Post by H-Alpha »

Bob Yoesle wrote: Mon May 27, 2024 4:00 am Hi Alexandros,

For double stacked front etalons I'd consider Solarscope 50, 60, or 70 etalons, or Lunt 60 or 100 etalons.

If you used the etalon(s) properly located with an objective with the same f ratio and a smaller focal length and objective diameter than the 130 you'd have a larger Jacquinot spot. But if they have the contrast irregularity form etalon plates that are uneven this issue will likely remain.

I would think that once you've pointed the telescope at the sun 15-20 minutes should be enough time for the etalons to stabilize. This might vary depending on the ambient temperature and other factors. Careful observation will reveal when they are stabilized and don't change much after the initial time period.

Bob
Thank so much Bob!

You always find the time and have the patience to answer all the questions in depth!
You have helped so many people that want to do/understand solar astronomy. :-)
:bow :bow :bow

Have a nice day,
Alexandros


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Re: Can I improve my problematic DS images in post-processing?

Post by Carbon60 »

Hi Alexandros,

Consider building FDs using multiple pane mosaics. With a suitable Barlow you’ll keep within the sweet spot. This is what I do with my triple stacked Lunt 60, as FDs straight from the scope’s natural focal length are not uniform at all.

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Re: Can I improve my problematic DS images in post-processing?

Post by allhoest »

H-Alpha wrote: Sun May 26, 2024 1:18 am ...
Anyway, this likely cannot change. My question is if you think there is any possible way to achieve a bit more pleasant and homogeneously lighten photos in post-processing. In other words, if I could automatically make the darker areas lighter or the opposite.
...
I used in the past a photoshop script for artificial flat application.
It is called SyntheticFullDiskFF

You may give a try.
Google for it.
Otherwise I have a backup on my laptop.

CS
Alex


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Re: Can I improve my problematic DS images in post-processing?

Post by H-Alpha »

allhoest wrote: Mon May 27, 2024 7:45 pm
I used in the past a photoshop script for artificial flat application.
It is called SyntheticFullDiskFF

You may give a try.
Google for it.
Otherwise I have a backup on my laptop.

CS
Alex
Thanks a lot Alex!
I could not find this script.
Can you please send it to me as you kindly suggested?

Best wishes,
Alexandros


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Re: Can I improve my problematic DS images in post-processing?

Post by H-Alpha »

Carbon60 wrote: Mon May 27, 2024 7:25 pm Hi Alexandros,

Consider building FDs using multiple pane mosaics. With a suitable Barlow you’ll keep within the sweet spot. This is what I do with my triple stacked Lunt 60, as FDs straight from the scope’s natural focal length are not uniform at all.

Stu.
Thanks a lot Stu.
I will give it a try during the next days. I think I would need more than 12 panes, but it may be worthy anyway.

Best wishes,
Alexandros


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Re: Can I improve my problematic DS images in post-processing?

Post by allhoest »

H-Alpha wrote: Fri May 31, 2024 12:26 am
allhoest wrote: Mon May 27, 2024 7:45 pm
I used in the past a photoshop script for artificial flat application.
It is called SyntheticFullDiskFF

You may give a try.
Google for it.
Otherwise I have a backup on my laptop.

CS
Alex
Thanks a lot Alex!
I could not find this script.
Can you please send it to me as you kindly suggested?

Best wishes,
Alexandros
Here a link with WeTransfer.
If you don't like to connect to links, pls send me a PM with your email address.
https://we.tl/t-f0tWEm7Qe6

When donwloaded, you have to remove the space in the extension -->> .atn
The script has to be loaded as "action" in PS, but I can't remember the procedure. You may need to google to find out the procedure.

I hope that it can help you.

CS
Alex


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Re: Can I improve my problematic DS images in post-processing?

Post by H-Alpha »

Thanks a lot Alex!

I just downloaded it and know the procedure to include it in actions.

Will try it asap and may come back to you if needed.

Best wishes,
Alexandros


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Re: Can I improve my problematic DS images in post-processing?

Post by Oak »

A similar approach would be to apply a bandpass filter using something like ImageJ to remove structures that are about the size of your inhomogeneity. Here is the result of a FFT bandpass filter between 50 and 1 pixel. (FIJI ImageJ menu Process/FFT/Bandpass Filter). Of course more tweaking would be necessary and it flattens the disk a bit much.
-Derek
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50pxFFTv2_SS-DS H-alph inhomogeneity.jpg
50pxFFTv2_SS-DS H-alph inhomogeneity.jpg (263.07 KiB) Viewed 358 times


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Re: Can I improve my problematic DS images in post-processing?

Post by H-Alpha »

Oak wrote: Sat Jun 01, 2024 1:47 am A similar approach would be to apply a bandpass filter using something like ImageJ to remove structures that are about the size of your inhomogeneity. Here is the result of a FFT bandpass filter between 50 and 1 pixel. (FIJI ImageJ menu Process/FFT/Bandpass Filter). Of course more tweaking would be necessary and it flattens the disk a bit much.
-Derek
Dear Derek,

This is an amazing tool! Thanks so much!
I had no idea of the existence of this software.

Best wishes,
Alexandros


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Re: Can I improve my problematic DS images in post-processing?

Post by Oak »

No problem. It's a free image analysis program developed by NIH. Although heavily skewed towards biological processing, there are a number of packages for astronomy and many of the tasks are general.

Free download and wiki:
https://imagej.net/software/fiji/

Astronomy focused package astroimagej

http://astro.phy.vanderbilt.edu/~vida/aij.htm


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Re: Can I improve my problematic DS images in post-processing?

Post by Ivan »

Hello, Alexandros!

I share your disappointment. I have always believed that large telescopes are designed to show the entire disk.
There is nothing to add after Bob's recommendations. It may make sense to go through all the configuration steps first. Unscrew and remove the pistons, screw them back on. Looking at the laptop screen to find a common spot. You need to pay attention to the maximum contrast, if it is difficult, then look at the double limb, it should disappear. Next, move the Sun around the frame, keep an eye on one area (the contrast of which you consider optimal) and see exactly where the contrast begins to disappear. This is how you define the boundaries of the spot suite. You can also spin the BF and see if there are any changes.
Alexandros, your task is not to lose interest and not to be disappointed. Remember that you can always shoot mosaics, you can use your DS system for close-ups, you can rearrange your etalons to refractors of 150 mm or more and get images of a larger scale.
I would also recommend that you do not invert the limb in the photo, this makes it difficult to understand whether it has disappeared or not.
I also understand how frustrating it is not to receive a response from LSS. I've come across this more than once, but I wanted to make a purchase and haven't received a response for months.

Ivan


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