Having trouble tuning Lunt LS80MT Double Stack

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Having trouble tuning Lunt LS80MT Double Stack

Post by AJ132 »

I recently acquired a LUNT LS80MT modular scope with the SFPT pressure tuned double stack filter module. I have had the scope out a couple of times, but I am having trouble getting the double stack etalons tuned correctly. Based on the recommendation from Lunt, I start out by removing the second etalon and tuning with just one etalon. I then attach the second etalon and attempt to tune it. However, I never achieve a clear image following this approach. When I put on the second etalon it throws the focus way out of whack which requires me to adjust the back focus of the B1800 blocking filter to find focus again. Once I find focus, adjusting just the second etalon does not provide a clear image. The best image I have been able to attain is by cranking the first etalon closest to the objective end of the scope all the way in and then adjusting the second etalon until I can see some detail. My setup includes a ZWO ASI178 attached to the B1800 blocking filter (see attached image).

So far this has been a frustrating experience. I have heard so many good things about this scope that I am pretty sure it I user error and not the scope. I thought I would come here to see if I can get some help. Is there a better tuning sequence I can follow that does not require me to remove the second etalon? Also, it seems odd that I would have to crank the first etalon all the way to get a clear image when using the second etalon. Does this sound correct?

I am also wondering if part of my issues is that my back focus for the camera is not correct. I just assumed the eyepiece mount was threaded for a reason which why I have the camera attached there. I have not been able to find any information regarding the back focus requirement for the B1800 block filter so just guessing on the camera placement.

I would really appreciate some help/guidance from the gurus here that will hopefully put me on the path to better images.

Andrew J
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Re: Having trouble tuning Lunt LS80MT Double Stack

Post by EGRAY_OBSERVATORY »

Hello Andrew.
I am preparing a list of the order of what is normally required for getting the best out of one of the best instruments and the B1800 BF that you have.

Q. Are you using a Solar-tracking mount for ease of making scope/DS adjustments. ?
Q. Have you been trying to make the adjustments to both Etalons using just an eyepiece and if so what size ?
Q. I see you have the OPTEC QuickSync controller, which I am not familiar with - please confirm (from the picture) whether it just adjusts the
focusing of the B1800 unit from the scopes own focus-adjustable draw-tube ?

Perhaps a couple more overall pictures might assist...

Thanks
Terry


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Re: Having trouble tuning Lunt LS80MT Double Stack

Post by Bruce G »

Is this the configuration that you're using? If so, you don't have the drawtube adjusted properly.

As Terry suggested, get the camera out of the system and work visually at first until you're sure you have everything right. Adding the second etalon will indeed change the focus, since you change the length of the OTA by adding it. In general, whenever troubleshooting, make the system as simple as possible and change only one variable at a time.

"The best image I have been able to attain is by cranking the first etalon closest to the objective end of the scope all the way in and then adjusting the second etalon until I can see some detail."
I don't have the MT version (I have the earlier LS80THa), but I wouldn't think that Lunt would change much in the configuration. In my setup, the second etalon is added to the rear, between the first etalon and the focuser. It sounds like you have it the other way around


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Re: Having trouble tuning Lunt LS80MT Double Stack

Post by DeepSolar64 »

I am not much of an imager but I would certainly tune by eyepiece first before using a camera.


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Re: Having trouble tuning Lunt LS80MT Double Stack

Post by marktownley »

Hi There,

When you say you are not getting a clear image what exactly do you mean - can you elaborate?

At the moment the sun is blank, completely blank, and devoid of features. It can be very difficult to tune a double stack when the sun is like this. My advice, stick with single stack for the time being until we get some features to view, then you will see what the double stack unit is capable of. Get used to what you can see in single stack. Have you had / used a Ha scope before the 80?

Mark


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Re: Having trouble tuning Lunt LS80MT Double Stack

Post by EGRAY_OBSERVATORY »

Hello again Andrew,
Agreeing with what Mark has just said, it is imperative that the camera is not used until you are completely competent and satisfied that you are able to get the basic set-up working as it should be for the best "Mk.1 Eyeball" - visually looking through a (say 20mm) eye-piece and only without the DS at first.

To try and do it all (including adjusting the PC and Double Stack) is a little like chasing a Bull around a field.

I've just revamped my Solar Observatory which included new computer-gear etc. and because of some previous problems have gone back to the basics for setting-up the three Solar-scopes (Ha, Cal-K and WL), which definitely has worked well so-far, with just waiting for some decent activity on the Sun's surface for sorting the White-Light scope and as Mark said, "the Sun is blank" so patience is required.

Just start at the basic setup, with slow & slight adjustments, then you will appreciate what really can be achieved.

Once you can reply to both Mark and myself, I'm sure you will then be able to enjoy the opportunities that your excellent LS80MT will be able to give you...

CLEAR SKIES & Best Wishes

Terry


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Re: Having trouble tuning Lunt LS80MT Double Stack

Post by AJ132 »

EGRAY_OBSERVATORY wrote: Sat Sep 19, 2020 9:51 pm Hello Andrew.
I am preparing a list of the order of what is normally required for getting the best out of one of the best instruments and the B1800 BF that you have.

Q. Are you using a Solar-tracking mount for ease of making scope/DS adjustments. ?
Q. Have you been trying to make the adjustments to both Etalons using just an eyepiece and if so what size ?
Q. I see you have the OPTEC QuickSync controller, which I am not familiar with - please confirm (from the picture) whether it just adjusts the
focusing of the B1800 unit from the scopes own focus-adjustable draw-tube ?

Perhaps a couple more overall pictures might assist...

Thanks
Terry
Hi Terry.

Q1: Yes, the scope is mounted on Astro-Physics GTO Mach1 Mount with the Rate set to Solar
Q2: I have not tried using an eyepiece with the scope in it's double stack configuration. However, I did use the Lunt Zoomable eyepiece (21 - 7) in it's single stack configuration.
Q3: Yes, the auto focus motor is an Optec QuickSync. It is the same as the HSM focus motor sold by Starlight Intstruments (Optec makes these focus motors for Starlight)

Let me know what additional pictures would be helpful and I would be happy to post them.

Thank you for your assistance.

Andrew J


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Re: Having trouble tuning Lunt LS80MT Double Stack

Post by AJ132 »

marktownley wrote: Sun Sep 20, 2020 6:51 am Hi There,

When you say you are not getting a clear image what exactly do you mean - can you elaborate?

At the moment the sun is blank, completely blank, and devoid of features. It can be very difficult to tune a double stack when the sun is like this. My advice, stick with single stack for the time being until we get some features to view, then you will see what the double stack unit is capable of. Get used to what you can see in single stack. Have you had / used a Ha scope before the 80?

Mark
Hi Mark.

This is my first ever Solar Scope. I have a TEC 140 I use for night time AP, but recently took the plunge into solar to try and get more utility out of my setup. With the stock red etalon cranked all the way in and the second etalon behind it (towards the eyepiece) I was able to get some clarity (see attached photo), but I guess I was expecting to see more. Like you suggested, I might be better off waiting until there is more activity. I was just trying to get some practice using the scope and getting some images before there is more activity.

Andrew J
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Re: Having trouble tuning Lunt LS80MT Double Stack

Post by AJ132 »

EGRAY_OBSERVATORY wrote: Sun Sep 20, 2020 12:36 pm Hello again Andrew,
Agreeing with what Mark has just said, it is imperative that the camera is not used until you are completely competent and satisfied that you are able to get the basic set-up working as it should be for the best "Mk.1 Eyeball" - visually looking through a (say 20mm) eye-piece and only without the DS at first.

To try and do it all (including adjusting the PC and Double Stack) is a little like chasing a Bull around a field.

I've just revamped my Solar Observatory which included new computer-gear etc. and because of some previous problems have gone back to the basics for setting-up the three Solar-scopes (Ha, Cal-K and WL), which definitely has worked well so-far, with just waiting for some decent activity on the Sun's surface for sorting the White-Light scope and as Mark said, "the Sun is blank" so patience is required.

Just start at the basic setup, with slow & slight adjustments, then you will appreciate what really can be achieved.

Once you can reply to both Mark and myself, I'm sure you will then be able to enjoy the opportunities that your excellent LS80MT will be able to give you...

CLEAR SKIES & Best Wishes

Terry
Hi Terry.

Good advice. I will take the the camera out of the equation for now until I have more practice tuning the etalons with just an eyepiece. I was just curious of there was some "rules of thumb" to follow when attempting to tune a double stack. But it sounds like it really comes down to trial and error until you find the right combination.

Thanks again for all the helpful feedback.

Andrew J


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Re: Having trouble tuning Lunt LS80MT Double Stack

Post by AJ132 »

Bruce G wrote: Sun Sep 20, 2020 12:00 am Is this the configuration that you're using? If so, you don't have the drawtube adjusted properly.

As Terry suggested, get the camera out of the system and work visually at first until you're sure you have everything right. Adding the second etalon will indeed change the focus, since you change the length of the OTA by adding it. In general, whenever troubleshooting, make the system as simple as possible and change only one variable at a time.

"The best image I have been able to attain is by cranking the first etalon closest to the objective end of the scope all the way in and then adjusting the second etalon until I can see some detail."
I don't have the MT version (I have the earlier LS80THa), but I wouldn't think that Lunt would change much in the configuration. In my setup, the second etalon is added to the rear, between the first etalon and the focuser. It sounds like you have it the other way around
Hi Bruce.

Thanks for the suggestions. Note, I don't have the draw tube in the position I use for imaging in the picture. The draw tube is extended around 50mm as recommended by Lunt in their manual. As for the second etalon, it is mounted behind the "stock" red etalon. Unfortunately, Lunt does not have written instructions yet on how to make the conversion, but they did send me this picture of the LS80MT in it's DS configuration.
LS80MT DS Configuration
LS80MT DS Configuration
LS80MT-DS-PT_6010 (002).jpg (1023.36 KiB) Viewed 1228 times
Clear Skies.

Andrew J


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Re: Having trouble tuning Lunt LS80MT Double Stack

Post by Bruce G »

Andrew,

That's a fine image. There's simply nothing much to see up there right now. As soon as we get even a decent filament I think you'll see the difference. I'll second the suggestion of going single stack for a bit. But if the Sun perks up, you have clear skies and good seeing, you'll definitely want to get the second etalon out for some experimentation.

You should turn the second etalon so that its adjuster cap points 180 degrees from the first. It makes things much easier and there is no difference in the optics.

I haven't really seen much in the way of instruction for tuning double stacks either. As a starting point, begin with one etalon and focus the telescope. Adjust the etalon for minimum brightness and best uniformity* of brightness in the solar surface. Insert the second etalon and reset the focus. It doesn't have to be good. Adjust second etalon for the brightest image and touch up the focus.

That should get you close. From that point, it appears to be a subjective thing.

I have used a colored art pencil to mark my drawtube for various configurations - different Barlows, for example. I simply set the focuser at half of its travel, set up each configuration, getting close to focus using only the drawtube, then mark and label the drawtube at the place where it meets the focuser. The marks don''t have to be very accurate because you have half the travel of the focuser either side of your mark. I use one color of marks for single stack and a different color for double stack. So, once you have determined the correct drawtube length for any configuration, any time after that, just slide the drawtube to your mark and you'll be pretty close to focus with no hunting.


Bruce G

* The uniformity shows up better when you have a camera connected. We've been telling you to remove the camera at this point, but you really only need to do that while you're getting your bearings. Once you know what things are supposed to look like you'll be using the camera most of the time.
Last edited by Bruce G on Mon Sep 21, 2020 5:32 am, edited 1 time in total.


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Re: Having trouble tuning Lunt LS80MT Double Stack

Post by EGRAY_OBSERVATORY »

Thanks for the answers Andrew, which I'm sure not only helps me, but also Bruce and Mark to understand what gear you are using, as well as the image of the gear too.

I did look up your package on the Lunt website - which does also answer some of the basic questions.

A1. The Solar tracking mount question was simply to allow me to understand what you are trying to do and excellent for that mount.
A2. The zoom EP of 21 - 7 mm is ideal for the purpose as allows to zoom into the limb-edge for more accurate focusing, which should more or less
be the same setting for disk and prom activity, but maybe some very-fine extra-adjustment. Usually with changing between 21 & 7mm, refocusing
is required, as with any other changes/additions to the basic set-up later.
A3. Looking at the Lunt picture, tells me that I at least do not have sufficient experience of that particular arrangement of the double-pressure-tuned
Etalons as you have, so I would prefer to learn also from what Bruce, Mark or others are saying, as it does make sense to me.

Remember though, do things slowly and mark the draw-tube (as Bruce suggests).

It is likely but not certain yet, that in the next two to three days, there should be some surface-detail (possibly including a Sun-spot) from within the eastern-limb, which will help you much to take advantage of (weather permitting).

I now know that the LS80MT DS is also useful for night-time use, but obviously will mean that you will really need to know how to set it up in future -when and if you change between day and night use...

I'll be following with interest further advice given you and how you are getting on and especially when you are able to publish here some images, including any night-imagery on the "SUNLIT EARTH" forum of "SOLARCHAT" - of the Moon or Planets..

BEST WISHES & Clear Skies
Terry


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Re: Having trouble tuning Lunt LS80MT Double Stack

Post by AJ132 »

Bruce and Terry.

Thanks for the helpful advice. I have a direction to proceed. I will go back to single stack mode until i get a little more practice and then work up to double stacking once
I have that figured out a little bit better. I will also spend more time with the eyepiece until I get more practice and add back the camera once I am able to get good results at the eyepiece. I also like the colored pencil idea. Should help create a more repeatable process.

I really appreciate all the help and support. What a great forum.

Clear Skies,
Andrew


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Re: Having trouble tuning Lunt LS80MT Double Stack

Post by DeepSolar64 »

I considered strongly on buying a Lunt 80 or Lunt 100 just a little while back. I ended up getting a much better deal on a Coronado 90. The LS80MT is a fine instrument no doubt.


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Re: Having trouble tuning Lunt LS80MT Double Stack

Post by EGRAY_OBSERVATORY »

Thank you Andrew and just looking at the latest SDO imagery, you will not have to wait long for something to savour on the N.E. Limb of the disk,
as you will already have a large prominence-area and probably soon-after some Sun-spots etc., to enjoy through the EP with a single Etalon.

If you are happy, with that view, then why not try the camera instead of the EP, if time allows with just adjusting the focus only, to help you get accustomed to what is involved. If it doesn't work well the first time, go back to the first stages and look for the possibility of changing the positions of the draw-tube(s) of the B1800, camera and any another - keeping that one Etalon as is...

That will also give you the opportunity of making any adjustments to the imaging-software on the PC such as image timings, etc.

If you can use say SharpCap software, there are at least three options that may need setting and these can be a little different for capturing surface-detail and/or prominences in Ha. Still keeping to the one Etalon for the moment...

All the Best
Terry


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Re: Having trouble tuning Lunt LS80MT Double Stack

Post by BGazing »

Coming back to this...received my DS module a while ago, but we literally have a month-long monsoon here, can't get a view of the Sun at all. Just clouds and downpour.
Is SS focusing first a must? Can one burp the DS module and then first adjust SS through it? If temperature/pressure changes significantly, does one need to adjust both modules? Which one first? Just trying to cut out the frustration if the Sun ever shines again. :)
I know that higher temperature and humidity means one has to crank PT cylinder in to keep it on band...and I assume the effect should be comparable for both modules?


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Re: Having trouble tuning Lunt LS80MT Double Stack

Post by marktownley »

Yes, get SS tuning sorted first and then add the double stack and tune that. Leave the SS etalon tuning alone.


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Re: Having trouble tuning Lunt LS80MT Double Stack

Post by BGazing »

marktownley wrote: Sun Jun 04, 2023 5:06 am Yes, get SS tuning sorted first and then add the double stack and tune that. Leave the SS etalon tuning alone.
Interestingly, I grabbed a couple of minutes yesterday and today to test this. On both occasions it was cloudy, yesterday oppressively humid, today windy.
I adjusted yesterday as per norm, SS than DS. Today tried DS straight out and it did not look okay, no matter how much I played with the DSPT. Finally I adjusted the SSPT and voila...details popped out (sort of, given the conditions). I guess once you are 'in the ballpark' you can adjust, especially as the conditions change (temp and humidity)? It is not the situation of 'you have to take out DS module every time you touch the SS PT' I guess?


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Re: Having trouble tuning Lunt LS80MT Double Stack

Post by pedro »

I agree with Mark, try first SS abd then try DS. It iw not easy to adjust the two etalons, with practice you will get there


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