19 replies to this topic

[TrollShark]

Hello,

 

I'm experiencing an issue with capturing details over the entire solar disk, and I was just hoping for some input as I'm losing a lot of detail. Is this just an issue with tilt? I'm using a Lunt LS50THa with a ZWO 120mm Mini on an EQ6R pro. The images I took were just snapshots using sharpcap at MONO16, .32ms exposure, and 22 gain, saved as .fits and exported as .png in GIMP, otherwise no post-processing. I feel like I'm going crazy with this, and I'd love to know if it's just me or if it's a telescope issue. I am using a helical focuser and not the feather touch focuser from Lunt, but the "Rubber band method" of removing the blocking filter tilt did not resolve the issue.

 

Images:

https://imgur.com/a/pXBEY4j

 

Also I'm sorry for any incorrect formatting, I've never posted here before.

[MalVeauX]

Hi,

 

Looks like banding, the dark strip down the middle of the disc and two flanking brighter off-band sections. This is common to systems with excess pressure or excess tilt to come on band, which is usually because the etalon is pre-tuned shifted too far and not appropriate for the elevation (air pressure related) of where you're using it, so it takes excess tilt (blue shift) or pressure (red shift) to attempt to come on band, and the result is usually this: banding. Since this is a pressure tuned scope, increasing pressure will red shift.

 

Are you having to twist the pressure tuner down (righty tighty) almost all the way that will go?

Have you burped the pressure tuner (turn it to the left until it releases and it will off gas internal pressure and equalize with ambient, then thread it back on)?

 

Very best,

[TrollShark]

Hi,

 

Looks like banding, the dark strip down the middle of the disc and two flanking brighter off-band sections. This is common to systems with excess pressure or excess tilt to come on band, which is usually because the etalon is pre-tuned shifted too far and not appropriate for the elevation (air pressure related) of where you're using it, so it takes excess tilt (blue shift) or pressure (red shift) to attempt to come on band, and the result is usually this: banding. Since this is a pressure tuned scope, increasing pressure will red shift.

 

Are you having to twist the pressure tuner down (righty tighty) almost all the way that will go?

Have you burped the pressure tuner (turn it to the left until it releases and it will off gas internal pressure and equalize with ambient, then thread it back on)?

 

Very best,

I have burped the unit each time I've used it (I know it isn't needed each time you use it, but I was in different elevations each time I've used it so far), and I have twisted it almost all the way it will go. Around the point where it gets really hard to twist is when the details start to show up, as far as I've noticed at least.
 

[MalVeauX]

Around the point where it gets really hard to twist is when the details start to show up, as far as I've noticed at least.
 

Then your etalon is pre-tuned too far blue shifted for your elevation and its requiring almost all your pressure tuner's pressure to red shift it back on band which results in the banding. You can't fix this. The etalon is too blue shifted to begin with for your elevation. You may want to contact Lunt and see what can be done about it. Ideally you want the etalon to come on band with the least amount of pressure (or tilt) to avoid this and have higher uniformity. This is not due to tilt anywhere in your system typically.

 

Very best,
 

[gstrumol]

Welcome to CN and the solar forum!

 

First, some terminology. I believe you are referring to that U-shaped feature at the top of your images? That is a filament, not a prominence, although once it goes over the rim from our viewpoint it is called then a prominence.

 

Looking at your images I'd say they look both off-band and out of focus. I guess the first question is: can you achieve focus with your camera on this scope? I know there are some issues with this scope and the helical focuser, which is why I ask.

 

Then can you see the surface darken as you tighten the tuner? When it reaches max darkness you'll be on band (basically).

 

There is also something called a 'sweet spot' where the detail (once focused and tuned properly) will appear sharpest. You're experiencing it as you let the sun move across the FOV of the camera. You'll need to learn where it is and how to size and position the sun for the best view.

[jwestervelt]

That's the "Jacquinot spot".  Your etalon has a sweet spot that should be very close to the optical axis.  Sometimes, however, the etalon is not collimated well with your objective and it can be off to the side of the sensor a bit.  In addition, the spot could be too small to adequately fit the image of the sun.  Sometimes the addition of a second etalon (double-stacking) can help mitigate it.

[jwestervelt]

The area between the blue lines is your sweet spot.  I have a similar issue with my scope which is also a Lunt50.  I used to have a mostly round sweet spot that was shifted to one side of the sensor, but I took the scope in and Lunt tried to make it better, but in the end it ended up similar to yours.  I do not know what the solution is, or what would cause that shape.  Maybe some optical tech on here could shed some insight.  I'd be willing to have Lunt keep my scope for a month or two if necessary just to try to get it back to where i could have the sun fully in the spot. 

Edited by jwestervelt, 19 April 2024 - 01:54 AM.

[jwestervelt]

I found the answer.  The etalon is bad.

https://solarchatfor...pic.php?t=30881
 

 

It looks like I am probably going to have to save up for a replacement now. 

[gstrumol]

What day was your image taken? You can always go to the GONG image from that day to see what was visible on the disk, so you'll know what to expect and look out for. CN member SgrB2 posts them each day so just search the forum for his post on that day to find it.

 

Also, there is a big difference between what you can see in a snapshot and what you can get by processing a video.

Edited by gstrumol, 19 April 2024 - 09:52 AM.

[TrollShark]

Welcome to CN and the solar forum!

 

First, some terminology. I believe you are referring to that U-shaped feature at the top of your images? That is a filament, not a prominence, although once it goes over the rim from our viewpoint it is called then a prominence.

 

Looking at your images I'd say they look both off-band and out of focus. I guess the first question is: can you achieve focus with your camera on this scope? I know there are some issues with this scope and the helical focuser, which is why I ask.

 

Then can you see the surface darken as you tighten the tuner? When it reaches max darkness you'll be on band (basically).

 

There is also something called a 'sweet spot' where the detail (once focused and tuned properly) will appear sharpest. You're experiencing it as you let the sun move across the FOV of the camera. You'll need to learn where it is and how to size and position the sun for the best view.

 I can achieve focus with the helical focuser. I do see it get darker when I tune it, but it feels like I go out of tune when I let it go all the way dark. It feels like the sweet spot doesn't cover the entire disc no matter how much I tune though. I'll try to see if I can play with it some more soon (pending the weather).

 

What day was your image taken? You can always go to the GONG image from that day to see what was visible on the disk, so you'll know what to expect and look out for. CN member SgrB2 posts them each day so just search the forum for his post on that day to find it.

 

Also, there is a big difference between what you can see in a snapshot and what you can get by processing a video.

I took this on the 12th of this month at around 2:40pm central time. I'll check gong to see what was visible, per your suggestion.

 

I have tried processing but I just end up with a bright or dark spot in the center with this data.

 

And thank you for your responses by the way!
 

[gstrumol]

 I can achieve focus with the helical focuser. I do see it get darker when I tune it, but it feels like I go out of tune when I let it go all the way dark. It feels like the sweet spot doesn't cover the entire disc no matter how much I tune though. I'll try to see if I can play with it some more soon (pending the weather).

 

I took this on the 12th of this month at around 2:40pm central time. I'll check gong to see what was visible, per your suggestion.

 

I have tried processing but I just end up with a bright or dark spot in the center with this data.

 

And thank you for your responses by the way!
 

No problem - we're here to help!

 

Here is the GONG image from the 12th and your image (rotated to match it):

 

 

I can see hints of some of the other filaments (besides the U shaped one, of course), but I'd expect to see them more visibly, even with a snapshot.

 

How do you determine that you have focus? On my PST/DSLR setup I set the tuning all the way to the right (so a blank disk with only the sunspots visible) and zoom in to one of the spots. I focus there. Then I turn the tuning back the other way until I see the disk start to get dark. I go slowly here until I feel it's at the optimal point. If I go further it will lighten again (meaning I've passed it), so the optimal spot isn't all the way to the left! You have to go back and forth a bit around there to get it right.

 

When you say 'I have tried processing' do you mean on the snapshot, or did you take a video and work on that? Sometimes you can squeeze out some detail with a snapshot, but the video will give you the best possible image. For example:

 

(click to enlarge)

 

Bottom left is a snapshot processed in GIMP; middle is from a video.

[TrollShark]

No problem - we're here to help!

 

Here is the GONG image from the 12th and your image (rotated to match it):

 

compare.jpg

 

I can see hints of some of the other filaments (besides the U shaped one, of course), but I'd expect to see them more visibly, even with a snapshot.

 

How do you determine that you have focus? On my PST/DSLR setup I set the tuning all the way to the right (so a blank disk with only the sunspots visible) and zoom in to one of the spots. I focus there. Then I turn the tuning back the other way until I see the disk start to get dark. I go slowly here until I feel it's at the optimal point. If I go further it will lighten again (meaning I've passed it), so the optimal spot isn't all the way to the left! You have to go back and forth a bit around there to get it right.

 

When you say 'I have tried processing' do you mean on the snapshot, or did you take a video and work on that? Sometimes you can squeeze out some detail with a snapshot, but the video will give you the best possible image. For example:

 

OK.jpg

(click to enlarge)

 

Bottom left is a snapshot processed in GIMP; middle is from a video.

so when I go to check focus I'll zoom in on sun spot, and/or the edge of the disc,  and focus in/out until I get it as sharp as I can. After that I'd when I'll tune the etalon. so maybe that throws off my focus a little bit, but would being out of focus create banding like that?

 

As for processing, I took 1000 frame subs using sharpcap in SER file format, then stacked in autostakkert and then stretched in imppg. Then I'll save that and take it to Pixinsight for curve adjustments. probably not the best place for that part but idk how to use gimp. I just can't ever pull out the detail though

[gstrumol]

A) so when I go to check focus I'll zoom in on sun spot, and/or the edge of the disc,  and focus in/out until I get it as sharp as I can. After that I'd when I'll tune the etalon. so maybe that throws off my focus a little bit, but would being out of focus create banding like that?

 

B) As for processing, I took 1000 frame subs using sharpcap in SER file format, then stacked in autostakkert and then stretched in imppg. Then I'll save that and take it to Pixinsight for curve adjustments. probably not the best place for that part but idk how to use gimp. I just can't ever pull out the detail though

A) tuning the etalon might tweak the focus a tiny bit, but it would not produce banding. That happens because of the sweet spot/region, and is affected by the quality of the etalon. My PST tunes by tilting; yours is a pressure tuning system. Either system should produce similar results.

 

B) Your process is quite good and reasonable. Looking at your snapshot I'd say that this however was doomed from the start because you need to have a fairly good amount of detail in the individual frames in order to get a good processed image. For example, here is a screenshot from a video I took on 3/29 and the final processed image using AS!3, iMPPG, and GIMP for postprocessing:

 

(click to enlarge)

 

I use an 8-24mm zoom EP attached to the DSLR to get focus on the sun in different sizes. This was setting the zoom to 8mm (largest possible image) which fills nearly all of the camera frame, as you can see.

 

In the individual frame you can see the surface details faintly, but they are there. The SW then just stacks them to increase the S/N ratio, basically. But if you had a 1000 images just like your single snapshot there would be no way for stacking and processing to create details that weren't there.

[TrollShark]

A) tuning the etalon might tweak the focus a tiny bit, but it would not produce banding. That happens because of the sweet spot/region, and is affected by the quality of the etalon. My PST tunes by tilting; yours is a pressure tuning system. Either system should produce similar results.

 

B) Your process is quite good and reasonable. Looking at your snapshot I'd say that this however was doomed from the start because you need to have a fairly good amount of detail in the individual frames in order to get a good processed image. For example, here is a screenshot from a video I took on 3/29 and the final processed image using AS!3, iMPPG, and GIMP for postprocessing:

 

StartToFinish.jpg

(click to enlarge)

 

I use an 8-24mm zoom EP attached to the DSLR to get focus on the sun in different sizes. This was setting the zoom to 8mm (largest possible image) which fills nearly all of the camera frame, as you can see.

 

In the individual frame you can see the surface details faintly, but they are there. The SW then just stacks them to increase the S/N ratio, basically. But if you had a 1000 images just like your single snapshot there would be no way for stacking and processing to create details that weren't there.

 

those results you shared, both raw and processed, were what I was hoping for when I purchased this telescope initially.

yeah that's what I was afraid of, and have been trying to express to the Lunt support team. It just sucks being unable to put it into words and confirm the issues the scope is experiencing. I spoke with them today and they informed me that they don't test their telescopes with cameras, only with visual observation which was very disheartening to hear.  Would you  happen to know if banding shows up very well through visual observation with one of these dedicated telescopes?

 

I guess ultimately I just need to hold out hope that they can fix it, or try and get some of my money back.

[gstrumol]

those results you shared, both raw and processed, were what I was hoping for when I purchased this telescope initially.

yeah that's what I was afraid of, and have been trying to express to the Lunt support team. It just sucks being unable to put it into words and confirm the issues the scope is experiencing. I spoke with them today and they informed me that they don't test their telescopes with cameras, only with visual observation which was very disheartening to hear.  Would you  happen to know if banding shows up very well through visual observation with one of these dedicated telescopes?

 

I guess ultimately I just need to hold out hope that they can fix it, or try and get some of my money back.

Yes, it does. With my PST visually (I typically use a 10mm Plossl which gives me a 40x mag and the full disk visible) I can move the sun around the FOV with the slo-mo knobs on the GEM mount, and I can see surface details appear and vanish as it moves around.

 

I guess I forgot to ask: can you see sharp surface detail visually (forget the camera)? If you can't then there's definitely something wrong with the scope. If you can, then it may be an issue with your camera system.

[TrollShark]

Yes, it does. With my PST visually (I typically use a 10mm Plossl which gives me a 40x mag and the full disk visible) I can move the sun around the FOV with the slo-mo knobs on the GEM mount, and I can see surface details appear and vanish as it moves around.

 

I guess I forgot to ask: can you see sharp surface detail visually (forget the camera)? If you can't then there's definitely something wrong with the scope. If you can, then it may be an issue with your camera system.

yes, I can. Although I don't know if it shows detail over the full disc. I only looked through it visually once, however I have used three cameras on it. Two were the same (player one Uranus c) and the other was the ZWO 120mm mini but experience the same results between all three cameras.

[gstrumol]

yes, I can. Although I don't know if it shows detail over the full disc. 

Easy way to check that. Before taking the scope out to view the sun check GONG to see what you should be able to see. I prefer the one from Chile as it is very high up on a mountain and it generally gives the sharpest views. You should be able to see everything on that GONG image (assuming decent seeing, of course), although you may have to move the sun around in the FOV to see it all, by moving through the sweet spot.

[TrollShark]

Easy way to check that. Before taking the scope out to view the sun check GONG to see what you should be able to see. I prefer the one from Chile as it is very high up on a mountain and it generally gives the sharpest views. You should be able to see everything on that GONG image (assuming decent seeing, of course), although you may have to move the sun around in the FOV to see it all, by moving through the sweet spot.

That's some very good advice! Hopefully the difference will be very readily apparent and they'll be able to fix it. I'm just going to assume that because I ordered it so close to the eclipse that it messed with the usual quality they normally put out due to the high demand. At the very least I'll look for the more apparent filaments and sun spots and compare that with GONG.

[gstrumol]

Good luck!! 

[TrollShark]

Update for anyone interested:

 

Lunt solar was very accommodating to my concerns and sent a shipping label to me to return the telescope for evaluation and repairs, and I'm extremely happy to report that it looks like all is well with the scope. I tested it out as soon as they got it back to me but didn't get a very conclusive result from the GONG telescope as suggested previously, but today I'm doing some more imaging with it after a fair time of not having clear skies, and it looks really really good! Still getting some lost data but I'm chocking that up to just me being inexperienced at using the telescope and probably some camera tilt that I will try to clean up later. Many thanks to everyone who helped me with this!

 

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