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Solar imaging question: camera lens sharper than refractor?

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#26 GuitsBoy

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Posted 20 April 2024 - 02:21 PM

It all depends on the lens / refractor.

 

I've owned Takahashi refractors made with legendary "japanese glass" costing upwards of $15,000 that are beat by the sharpness of a $400 Rokinon 135mm chinese camera lens.

At nearly the same focal length?  Boy, I'd sure be upset over that.   Unless youre trying to compare the sharpness of a 1000+ mm focal length instrument vs a 135mm camera lens, in which case I dont think anyone would be the least bit surprised.

But in my case, the cause of the blurring was identified as the cheap float glass Orion solar filter.   Both the K&F neutral density filter, as well as Baader solar film resulted in crystal clear images from the refractor - well, by my standards anyway.   Mystery solved.



#27 gbartha

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Posted 21 April 2024 - 03:33 PM

Fantastic images!  I read this post with great interest because I have also been puzzled by how to get sharper images of the prominences.  I also have an AT102EDii and was using a T2i DSLR to image.  I have an old Thousand Oaks glass filter that I use with my C80 and it works very well and it also fits the AT72EDii.  Thousand Oaks switched to film filters and I compared that to my glass filter and strongly preferred the glass filter for visual use (sharper and better color to my eyes) so I ordered more glass filters from Spectrum.  My tests shots of the Sun were blurry like yours but I thought that was a limitation of my scope/camera and local seeing conditions which are generally bad.  Seeing conditions in Arkansas where I was for the eclipse were very good and it seemed clear what the best focus was.  I used zoomed in images on my computer to focus so there shouldn't be any uncertainty.  The filter removal is not supposed to affect focus either.  But I still ended up with less sharp prominences than I hoped for with my AT72EDii and even using my AT102ED with a dedicated astrocam which did a little better.  I was stunned by your test shot of the Sun with your new filter.  I can only get images like that with my AT102ED using lucky imaging.  So I am inclined to think your AT72EDii is the winner of the telescope lottery and mine is a dud.  My AT72EDii does not outperform (apart from color) my Orion GoScope (cheap 70 mm achromat) in a side by side comparison on Jupiter.  I had chalked that up to the GoScope being a very good example and the limitations of short focus refractors but now think my scope is not a good one.  It is hard for me to believe that my visual comparison of the filters would be misleading for photographic use.  I got stunning visual views of the eclipse with the glass filter during the partial phases and without it during totality without refocusing.  I have seen others compare good glass filters to film with only a slight edge to film.  I noticed that you also used an astrocamera with the AT72EDii.  How did you balance the colors?  Did you do any stacking?


Edited by gbartha, 21 April 2024 - 03:36 PM.


#28 GuitsBoy

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Posted 21 April 2024 - 04:57 PM

Fantastic images! I have seen others compare good glass filters to film with only a slight edge to film.  I noticed that you also used an astrocamera with the AT72EDii.  How did you balance the colors?  Did you do any stacking?

Thank you very much, I appreciate it.     If you havent already tried your AT102ED with a baader film filter, or an optical glass ND filter, you owe it to yourself (and your scope) to at least try it.  The cool thing about solar is that its so bright, its no big deal if you really reduce the aperture quite a bit.   You can get those K&F ND100000 filters I used for between $17 and $24 on amazon depending on size.  You might even pick up an open box one for cheaper after all the shady people return theirs after using it for the eclipse.   Or that small half sheet of baader film was 22 bucks shipped, and I made quite a few filters out of it.  You can make a much smaller filter than your 102mm aperture.  But anyway, since its so cheap, you might as well give it a try before blaming the scope.   Like I said, the old glass filter was a HUGE source of blur, and moving to either the ND or the film was a BIG improvement.   I'm not sure why it seems to affect photographic use more than visual.

As far as my images, there was quite a bit of the usual sharpening in photoshop and camera raw to get the detail in the sunspots to come out, but yes, I'm quite happy with that little scope, its been a heck of a performer on nebulas for a few years now, but it was nice to try something new.

To be perfectly honest, I much prefer the DSLR for solar compared to the cooled astro cam.  Its very clunky to find a good exposure length with the camera.   Gain bottoms out at 100 and wont go lower.  And overall, NINA is not a great fit for taking pictures of the eclipse, especially with the autostretch baked in.   But, since its the tool I'm used  to, I was able to make it work, and the advanced scripting / sequencer functioned perfectly.  I didn't find processing / color correction to be much different between OSC and DSLR, though its a pain to have to convert the FITS files to TIFF.  I found ASTAP was the easiest to do a quick conversion with.  The only stacking of the eclipse was the HDR stack to exaggerate the corona.  Those images were from the DSLR for the wider field of view.   I took five brackets of 12 photos each in increasing exposure length and iso.    I stacked the middle two brackets for a total of 14 images.  Stacking was done in photoshop with a smart object layer and mean mode.  Its all new to me, but there are plenty of howtos out there on youtube.  Otherwise all the images were single shots, or simple composite shots of 2 or 3 images.  Nothing crazy.


Edited by GuitsBoy, 21 April 2024 - 05:03 PM.


#29 gbartha

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Posted 21 April 2024 - 08:27 PM

As far as my images, there was quite a bit of the usual sharpening in photoshop and camera raw to get the detail in the sunspots to come out, but yes, I'm quite happy with that little scope, its been a heck of a performer on nebulas for a few years now, but it was nice to try something new.

To be perfectly honest, I much prefer the DSLR for solar compared to the cooled astro cam.  Its very clunky to find a good exposure length with the camera.   Gain bottoms out at 100 and wont go lower.  And overall, NINA is not a great fit for taking pictures of the eclipse, especially with the autostretch baked in.   But, since its the tool I'm used  to, I was able to make it work, and the advanced scripting / sequencer functioned perfectly.  I didn't find processing / color correction to be much different between OSC and DSLR, though its a pain to have to convert the FITS files to TIFF.  I found ASTAP was the easiest to do a quick conversion with. 

Thanks for the reply.  I do plan to test the ND filter you suggested.  In contrast to you, I have yet to be happy with anything my AT72EDii has done.  I haven't used it much but I thought the stars were a bit bloated in the few photos I took with it and the focus was done by NINA.  I found that reducing the aperture makes visual use much worse because the filter is far in front of the lens so you get a tunnel effect making it hard to look without drop outs.  It is also dimmer.  Neither of these are issues for a camera.  What is an issue for a camera is the loss of resolution from diffraction.  I don't know at what level this matters for prominences but I do know that an 80mm refractor is noticeable sharper on solar system objects than a 60mm one so I would think it does matter for the fine detail you were picking up. 

 

As for my images, I shot full resolution video with my Ares-C OSC camera and recorded .SER files with Firecapture.  I used PIPP to extract frames.  See an attached example of the color of my images.  The image is very orange indicating too much green.  I had the most success with the channel mixer in GIMP but it is very hard to get the right formula and I cannot even reproduce my best result.  FITS files recorded by NINA using the same camera for deep sky work after the eclipse show the same green tendency.  I thought this is normal but I don't have a lot of experience.  It sounds like you are saying that you didn't get the orange nightmare I have but I cannot understand then what I am missing.  It feels like I am missing something very basic about imaging.  Does your ASTAP conversion do something with the colors? 

Attached Thumbnails

  • sun_25f_LR1.1_UM3.4_sig2.4.jpeg

Edited by gbartha, 22 April 2024 - 02:59 PM.


#30 gbartha

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Posted 25 April 2024 - 05:03 PM

I still don't have a solution to my color balance issue but for the benefit of others struggling with this problem reading this, the current statement of my thinking is that:

1) GuitsBoy's astrocamera somehow had sensible color balance settings when he did his imaging.

2) My camera does not use sensible color balance settings out of the box.

3) Doing color balancing in post for this is nearly impossible.  Even conventional photography pros say color balance in post is very difficult and they have a much easier problem to solve.

4) There are many posts on CN about color balance and there is a lot inaccurate and misleading posts mixed in with more accurate ones.

5) One inaccuracy that is mentioned many times is that color balance doesn't matter and you can do want you need in post.  This may be true for some situations but it certainly isn't true for this case.

6) This won't fix my current images but for the future the best lead I need to follow is to try and set my astrocamera's white balance.  I don't know how to do this yet.  One would think that daylight settings for the IMX533 sensor with a standard Bayer matrix would be something you could just look up but so far I have not found that.  Using a white balance card and trying to manually adjust the settings would be another lead to try.


Edited by gbartha, 25 April 2024 - 05:05 PM.


#31 gbartha

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Posted 27 April 2024 - 08:28 PM

So I got a K&F ND100000 filter and put it on my AT102EDii and took test shots of the Sun.  Seeing was below average for here which isn't good making it hard to focus.  Seeing is almost never good here.  I took 50 shots hoping to get lucky with one of them.  I selected the best one for posting here.  I also posted an image taken with the Spectrum glass filter (the orange one) that was taken during good seeing in Arkansas for comparison.  I did not do any post processing of either image.  Neither are sharp and I don't see much difference in sharpness between them.  Perhaps I didn't get lucky enough with my test shots for a fair comparison but good seeing is rare here.  My impression is that there isn't much difference between the filters and that GuitsBoy has a much better AT102EDii than I do.  I never got a glimmer of anything as sharp as his during my hours imaging today.  I think it is more likely that the glass solar filter he had was a very bad one and that mine are normal.  Maybe someday I will get lucky with seeing for a more definitive test. 

Attached Thumbnails

  • SUN_LIGHT_Tv14000s_100iso_+41c_ND_20240427-20h01m25s740ms.jpg
  • IMG_2667.jpg

Edited by gbartha, 27 April 2024 - 08:31 PM.




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