New "built in" double stacked Lunt 80, anyone?

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New "built in" double stacked Lunt 80, anyone?

Post by dashour » Wed Aug 22, 2012 10:37 am

As I'm thinking of upgrading my PST to something more addicting, and increase my chances of going off the resolution deep end like some of the rest of you, this sure looks like a good way to do that. I hope Stephan reviews it sometime. Anybody seen or used it yet?

http://luntsolarsystems.com/blog/introd ... a-and-dsii



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Re: New "built in" double stacked Lunt 80, anyone?

Post by GaborKiss » Wed Aug 22, 2012 10:42 am

Hi dashour,

I can Seach in the forum older posts about Lunt80. Steve loves his one, some people had problems with it, or with quality, or with the built-in DSII as it gives a little halo around the disk. As far as I see the Lunt60DS systems are the most used systems, I have also heard that Lunt80 with 60DS (not the build in) works well, but then its no meaning to own a Lunt80 if you will use it anyway mostly with DS mode. The perfect would be the Lunt100DS, but its not really a grab n go system. So hope Lunt80DSII owners can give you their suggestions :) Gabor


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Re: New "built in" double stacked Lunt 80, anyone?

Post by dashour » Wed Aug 22, 2012 10:51 am

Thanks Gabor, it looked to me from Lunts web site that this was something brand new, but on second look I guess I was fooled by the date they placed on their internal "post" about it.



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Re: New "built in" double stacked Lunt 80, anyone?

Post by solarchat » Wed Aug 22, 2012 11:05 am

I did review it on my site...;)


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Re: New "built in" double stacked Lunt 80, anyone?

Post by dashour » Wed Aug 22, 2012 2:40 pm

Stephen, just read your review, thanks. so if I were to chose, for outreach, between the

Lunt 60,
Lunt 60 DS,
Lunt 80, and
Lunt 80 Internal DS,

Which would you advise? An experienced viewer does not have the same issues as a novice, and I'm more interested in the best scope amongst those 4 for outreach. please help! Many thanks.



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Re: New "built in" double stacked Lunt 80, anyone?

Post by solarchat » Wed Aug 22, 2012 2:56 pm

Well, I believe I am an expert in this field, unlike imaging...:)

amongst those scopes there is absolutely no doubt that I would get the LS80 single etalon scope.

(followed shortly thereafter by the external LS60F with screw on adaptor to doublestack it)

like this one.. its my portable grab and go that I used on Mauna Kea for the transit.





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Re: New "built in" double stacked Lunt 80, anyone?

Post by MetaFlow1 » Sat Feb 13, 2021 3:29 pm

solarchat wrote:
Wed Aug 22, 2012 2:56 pm
Well, I believe I am an expert in this field, unlike imaging...:)

amongst those scopes there is absolutely no doubt that I would get the LS80 single etalon scope.

(followed shortly thereafter by the external LS60F with screw on adaptor to doublestack it)

like this one.. its my portable grab and go that I used on Mauna Kea for the transit.
Stephen,
I am in the process of purchasing the LS 80 Observer package, what are the advantages and disadvantages of using the Lunt external 60 DS with adapter versus using the internal 80 DS? And is the difference worth the additional cost of the 80mm scope when considering the 60mm seems to perform extremely well in DS configuration? I really feel the 80mm aperture is exactly what I need, however, the internal DS etalon scares me. Any input would be appreciated.



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Re: New "built in" double stacked Lunt 80, anyone?

Post by SimonM » Sun Feb 14, 2021 2:44 pm

MetaFlow1 wrote:
Sat Feb 13, 2021 3:29 pm
What are the advantages and disadvantages of using the Lunt external 60 DS with an adapter versus using the internal 80 DS? And is the difference worth the additional cost of the 80mm scope when considering the 60mm seems to perform extremely well in DS configuration? I really feel the 80mm aperture is exactly what I need, however, the internal DS etalon scares me.
I asked the same question of the kind Lunt Support folks about two weeks ago. You might want to call them and ask them for the LS80MT, which option works best - they are the same price, but what works best depends upon the current configuration and not may have previously been the case with the LS80THa. Existing users will not need (or want) to move to the new model and won't necessarily know if there are pros and cons with the performance. It isn't a foregone conclusion that a smaller DS etalon isn't a good solution - aperture isn't everything and many users have stopped down their existing setup for optimal imaging.

The advantage of an external front-mounted etalon is, that the Sun's parallel rays are striking the etalon and that there is more separation between the second etalon and the first etalon to limit reflections and allow secondary images to be moved outside of the FOV.

The advantage of a second internally-mounted etalon is that the size can be reduced and so can the cost that is almost directly related to the area since it takes much longer to grind and finish a bigger etalon. The Sun's rays striking the second etalon need to be managed so there are additional lenses in front and behind the etalon to make it parallel. A combination of negative and positive lenses accomplish this for a point source however the Sun is an extended object, so it comes as a bit of a compromise. Added complexity doesn't always translate to being better.

Simon
Last edited by SimonM on Wed Feb 17, 2021 7:20 pm, edited 1 time in total.



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Re: New "built in" double stacked Lunt 80, anyone?

Post by Highbury Mark » Sun Feb 14, 2021 3:08 pm

The internal LS80 DS filter (and the internal 100mm DS filter) tend to cause a bright shadow around the solar disk which some people find annoying (I say ‘tend to’ because I don’t know if it’s a problem with every scope). There are now extra Lunt filters that diminish the shadows, but also add bulk and dim the rest of the view. There are other techniques for minimising the shadow, and brightening the overall image which you will find discussed elsewhere on this forum. Most LS80 owners seem happy with their scopes once these changes have been made, though whether it’s acceptable for a £7,000 scope to have such issues is debatable. I must say that when I was upgrading from an LS60DS last year, the ‘shadow’ stories put me off buying an LS80. Otherwise it would have been the perfect scope for me. For virtually the same price, I was able to get two external (70mm) Solarscope etalons which I’ve been delighted with.


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Re: New "built in" double stacked Lunt 80, anyone?

Post by marktownley » Mon Feb 15, 2021 6:53 am

SimonM wrote:
Sun Feb 14, 2021 2:44 pm
The advantage of an external front-mounted etalon is,
The sweet spot (jacquinot spot) is much larger with an external mounted etalon.


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Re: New "built in" double stacked Lunt 80, anyone?

Post by Bob Yoesle » Mon Feb 15, 2021 3:21 pm

Ditto to what Mark noted.

The internal DS etalon will generally have a brighter background and out-of-focus internal reflections which can be or are optimized with small amounts of tilt. An ideal solution - as has been discussed with my SM140/internal SM90, and implemented by George H. with his DS's LS80 - is placing a high-quality circular polarizer between the two etalon modules: https://schneiderkreuznach.com/en/photo ... /polarizer

This polarizer will unfortunately reduce image brightness by 50%. This can be mitigated by replacing the BG38 filter in the blocking filter with a suitable KG and UV/IR block filter(s), or a combined filter such as the BelOptik filter. https://beloptik.de/en/uv-ircut-on-kg3-filter/

A high-transmission nighttime H alpha and KG filter could also be used in the blocking filter in conjunction with the circular polarizer between the etalon modules.


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Re: New "built in" double stacked Lunt 80, anyone?

Post by SimonM » Mon Feb 15, 2021 7:01 pm

marktownley wrote:
Mon Feb 15, 2021 6:53 am
SimonM wrote:
Sun Feb 14, 2021 2:44 pm
The advantage of an external front-mounted etalon is,
The sweet spot (Jacquinot spot) is much larger with an externally-mounted etalon.
Does the sweet spot covers about 1.25 "diameters" of the Sun with the smaller LS 60/80 scopes, SS but also DS? In effect, the designs use the minimum etalon diameter and collimation combinations for the pressure-tuned internally-mounted etalon in the solar scope objective to give the desired "result", but at the lowest cost too and the front-mounted etalon doesn't compromise things (too much)?

Simon
Last edited by SimonM on Wed Feb 17, 2021 7:22 pm, edited 1 time in total.



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Re: New "built in" double stacked Lunt 80, anyone?

Post by george9 » Mon Feb 15, 2021 10:30 pm

As Bob noted, I have an LS80 DSII. The sweet spot is just a little bigger than the Sun, so it works fine; but I do tend to center proms if I want to look closely. It had a glow, which I eliminated by (1) installing a Kaesemann High Transmission Circular Polarizer between the two etalons, (2) replacing the BG38 glass with something with brighter transmission (KG3 is one choice), and optionally (3) shimming the DSII attachment so the two etalons are dead-on.

Why step #3: Before the polarizer, I found the glow least annoying when it was dead on. Although the main thing is just make sure the DSII is not tilted when you attach it to the scope. Its weight makes it easy to tilt. But now with the polarizer, I find if they are dead on, then the polarizer eliminates all glow, versus a very faint residual glow on one side.

I don't think I have seen any 80mm scope perform any better, and it matches the pre-Meade Coronado 90m double stack at NEAF. My LS80 DSII is not a special selected one. In fact I have two DSII etalons now, and they perform about the same.

Compared to a front-mounted DS, the dual pressure tuning lets me tune up- and down-band quickly for off-band activity in a way that would be awkward with one tilt and one PT. If fits in a small scope soft case and goes on a photo tripod with a small geared head. I always use a binoviewer (Denk II).

George



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Re: New "built in" double stacked Lunt 80, anyone?

Post by marktownley » Thu Feb 18, 2021 7:41 am

SimonM wrote:
Mon Feb 15, 2021 7:01 pm

Does the sweet spot covers about 1.25 "diameters" of the Sun with the smaller LS 60/80 scopes, SS but also DS? In effect, the designs use the minimum etalon diameter and collimation combinations for the pressure-tuned internally-mounted etalon in the solar scope objective to give the desired "result", but at the lowest cost too and the front-mounted etalon doesn't compromise things (too much)?

Simon
Hi Simon.

I can't speak for the newer modular scopes, however in the previous Lunt models the internal etalon sizes as follows:

LS50 - 20mm
LS60 - 30mm
LS80 - 50mm
LS100 - 50mm
LS152 - ??? (can anyone enlighten me?)

So, you can see, the LS80 provides the best aperture to etalon ratio, and the largest sweet spot, this is why there is so much preference for it. When you put a 60mm etalon on the front of a 80mm scope, even though the aperture is reduced this ratio remains the same - so 60mm DS filter on a 80mm Lunt scope means the free aperture of the etalon being used is 37.5mm, which is more than the 30mm etalon of the LS60. Hence the sweet spot on the LS80/DS60 setup would be 1.25x larger than a LS60/DS60 setup...

Incidentally, in terms of Coronados SMii series:

PST (40mm) - 20mm
SM60 - ??? (can anyone enlighten me?)
SM90 - 60mm

Knowing the aperture to (internal) etalon size ratio you can calculate the field angles and then the size of the sweet spot. Bob knows the maths with this and he may hop in :)

Mark


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Re: New "built in" double stacked Lunt 80, anyone?

Post by SimonM » Thu Feb 18, 2021 12:08 pm

marktownley wrote:
Thu Feb 18, 2021 7:41 am
[LS50 - 20mm
PST (40mm) - 20mm
The Lunt website has some SS etalon clear aperture sizes (LS50 = 26mm):

Aperture: Lunt @ 50mm / PST @ 40mm
Etalon Clear Aperture: Lunt @ 26mm / PST @ 18mm
LS152THa unobstructed internal HD Etalon

For front-mounted DS, no size is given (I assumed it was full width e.g. 50 on 50, 100 on 100) - but perhaps they only mean no or minimal central obstructions:

LS50FHa solar filter front-mounted non-obstructed hydrogen-alpha filter
LS60FHa H-Alpha Filter, 60mm front-mounted non-obstructed hydrogen-alpha filter
LS100FHA 100mm front-mounted minimally obstructed hydrogen-alpha filter

For the DSII the same internally-mounted DS is used on 80 and 100, I would have assumed that a bigger DS etalon would be required on the 100 to maintain ratios and further improve the performance, except that all scopes are f/7 and the position is behind the first SS etalon e.g. further back in the light "cone"?

Would it be too simplistic to compare a front-mounted DS etalon of the same size e.g. 50 on 50, 60 on 60, or 100 on 100, to say that the sweet spot is not further reduced by adding a DS to the existing SS, just because of etalon relative sizes? Or that a second internally-mounted DS always affects the existing SS sweet spot without additional information? The external front-mounted DS etalon will obviously, be much bigger than the equivalent internally-mounted SS etalon, using the LS60MT as an example of etalon clear aperture comparative sizes of 62mm (DS) and 36mm (SS).

How important in a DS setup is there a requirement to add a High-Resolution Filter (HRG 80) to cut/eliminate reflections? Is it always a problem and/or can a circular polarising filter also be used?

Simon
Last edited by SimonM on Thu Feb 18, 2021 6:48 pm, edited 1 time in total.



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Re: New "built in" double stacked Lunt 80, anyone?

Post by george9 » Thu Feb 18, 2021 1:00 pm

On the HRG filter, if you have two etalons next to each other, there is usually a reflection. If they are internal, then you cannot tilt one enough to throw them out of the field of view. The amount of glow varies, but generally there is something. Lunt's HRG filter is convenient and gets you 80 or 90% of the way there. And easy to use. A circular polarizer is better at controlling reflections but finicky with binoviewers. It takes some trial and error to get polarized binoviewers (which is most binoviewers) to have even illumination between the eyepieces. It mainly means put the polarizer in the right direction (to minimize the effect) and then rotating it for the best view (to eliminate the effect). Lunt's $70,000 300mm H-alpha scope uses a circular polarizer.

Scopes with one internal and one external etalon that I have looked through did not have reflections (maybe the front one was tilted). My double stack front mounted filter is easy to throw the reflections off the field of view.

George



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Re: New "built in" double stacked Lunt 80, anyone?

Post by marktownley » Sat Feb 20, 2021 9:41 am

SimonM wrote:
Thu Feb 18, 2021 12:08 pm
marktownley wrote:
Thu Feb 18, 2021 7:41 am
[LS50 - 20mm
PST (40mm) - 20mm
The Lunt website has some SS etalon clear aperture sizes (LS50 = 26mm):

Aperture: Lunt @ 50mm / PST @ 40mm
Etalon Clear Aperture: Lunt @ 26mm / PST @ 18mm
Hi Simon.

Don't believe everything the manufacturers tell you. The clear diameter of the LS50 etalon is 20mm. It may be 26mm overall, but only 20mm of it is used optically.

ImageP1000683 by Mark Townley, on Flickr

PST etalon is also 20mm free diameter. I've taken apart countless PSTs.

ImageP1000684 by Mark Townley, on Flickr

Mark


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Re: New "built in" double stacked Lunt 80, anyone?

Post by SimonM » Sat Feb 20, 2021 7:14 pm

We are told that plate area determines the approximate etalon cost e.g. bigger, means relatively longer to grind and finish, which seems very plausible. The cost of making stuff also has an influence on the final price, which affects the sales and also the viability of products. I'm still coming to terms with the fact that a larger DS externally-mounted etalon costs almost as much as the whole SS scope when it becomes smaller and internally-mounted, especially at the lower end.

For the 60mm it's a 3" to 2" plate size-reduction going internal e.g. the 36mm etalon clear aperture is from a 51mm plate (halving the cost is a good thing). Of course, the numbers given could be from the 80mm version and don't relate to the 60mm? If it was 30mm, and assuming that it could be made from a much smaller plate e.g. half the diameter (and a quarter of the cost), that would be simply fantastic.

They said for the PST, even less than 20mm appears to be used e.g. 18mm is the etalon clear aperture that is in the light path. The Lunt etalon has a lens on each side to control the collimation that adds slightly to the complexity and cost. Also, the etalon clear aperture is smaller than the lenses that surround it.

Simon



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Re: New "built in" double stacked Lunt 80, anyone?

Post by MetaFlow1 » Fri Feb 26, 2021 11:46 pm

SimonM wrote:
Sun Feb 14, 2021 2:44 pm
MetaFlow1 wrote:
Sat Feb 13, 2021 3:29 pm
What are the advantages and disadvantages of using the Lunt external 60 DS with an adapter versus using the internal 80 DS? And is the difference worth the additional cost of the 80mm scope when considering the 60mm seems to perform extremely well in DS configuration? I really feel the 80mm aperture is exactly what I need, however, the internal DS etalon scares me.
I asked the same question of the kind Lunt Support folks about two weeks ago. You might want to call them and ask them for the LS80MT, which option works best - they are the same price, but what works best depends upon the current configuration and not may have previously been the case with the LS80THa. Existing users will not need (or want) to move to the new model and won't necessarily know if there are pros and cons with the performance. It isn't a foregone conclusion that a smaller DS etalon isn't a good solution - aperture isn't everything and many users have stopped down their existing setup for optimal imaging.

The advantage of an external front-mounted etalon is, that the Sun's parallel rays are striking the etalon and that there is more separation between the second etalon and the first etalon to limit reflections and allow secondary images to be moved outside of the FOV.

The advantage of a second internally-mounted etalon is that the size can be reduced and so can the cost that is almost directly related to the area since it takes much longer to grind and finish a bigger etalon. The Sun's rays striking the second etalon need to be managed so there are additional lenses in front and behind the etalon to make it parallel. A combination of negative and positive lenses accomplish this for a point source however the Sun is an extended object, so it comes as a bit of a compromise. Added complexity doesn't always translate to being better.

Simon
Thanks for the response. I just ordered the 80mm Observer Package, with the DS, B1800 BF, and the Feather Touch focuser. I saw on one of the other posts where a poster was able to configure their DS module so that the reflections were pretty much eliminated without dimming the image severely. I'll have to see how it goes. This is my first solar scope, and hopefully, it will be my last if all goes well.



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