Lunt 60 mod options??

Frankenscope? Let's see it!***be advised that NOTHING in this forum has been safety tested and you are reading and using these posts at your own peril. blah, blah, blah... dont mess around with your eyesight when it comes to solar astronomy. Use appropriate filtration at all times...
Post Reply
Eddie
The Sun?
The Sun?
Posts: 4
Joined: Wed Aug 16, 2017 10:22 pm

Lunt 60 mod options??

Post by Eddie » Mon Jan 15, 2018 10:46 pm

Hello fellow solar surfers! i have a lunt LS60 single stack pressure tuned scope with starlight focuser and B1200, based on that are there any practical ways without reinventing the wheel that i could perhaps mate my scope or parts the of with lets say an 80 or 90mm small short tube frac?.

I am fairly tech savvy and would love the challenge, are there any out there who have done this, im sure there are many, please weigh in with suggestions, i guess an IR cut filter would be needed for the new frac which would somehow mate with the lunts existing etalon?

Thank you! i would love for anyone who has done this to give me a good schooling on what i am getting into and whether or not they'd recommend it to begin with, looking for more aperture without loosing a leg to Lunt lol.

User avatar
marktownley
Librarian
Librarian
Posts: 24236
Joined: Tue Oct 18, 2011 5:27 pm
Location: Brierley Hills, UK
Contact:

Re: Lunt 60 mod options??

Post by marktownley » Mon Jan 15, 2018 11:24 pm

Yes, lots of ways, lots of people have done it. Start searching the threads in the mods section.
Image
http://brierleyhillsolar.blogspot.co.uk/
Solar images, a collection of all the most up to date live solar data on the web, imaging & processing tutorials - please take a look!

antonello
Ohhhhhh My!
Ohhhhhh My!
Posts: 63
Joined: Tue Mar 24, 2015 12:34 pm

Re: Lunt 60 mod options??

Post by antonello » Tue Jan 16, 2018 3:23 pm

It's strange, it seems to me that the Lunt ls60 is equipped with a objective with only one lens, so it is not the most suitable instrument for a modification. To have a good quality with another (bigger) objective, it is necessary to replace the negative and the positive lens of the etalon collimator...

User avatar
Merlin66
Librarian
Librarian
Posts: 3137
Joined: Tue Dec 13, 2011 1:23 pm
Location: St Leonards, Australia
Contact:

Re: Lunt 60 mod options??

Post by Merlin66 » Tue Jan 16, 2018 11:46 pm

Some modders are getting good results by removing the original objective and mounting the Lunt OTA assembly in a larger aperture scope.
If the f ratio is similar to the original the negative and position lens will still work; the SA corrections may be affected.
"Astronomical Spectroscopy - The Final Frontier" - to boldly go where few amateurs have gone before
https://groups.yahoo.com/neo/groups/ast ... scopy/info
"Astronomical Spectroscopy for Amateurs" and
"Imaging Sunlight - using a digital spectroheliograph" - Springer

antonello
Ohhhhhh My!
Ohhhhhh My!
Posts: 63
Joined: Tue Mar 24, 2015 12:34 pm

Re: Lunt 60 mod options??

Post by antonello » Wed Jan 17, 2018 7:38 am

Unfortunately it's not like that.
What you write may be good for an achromatic lens, but it's not good if the objective of the solar telescope is a single lens.
Recently I read a topic in which a passionate Italian complained of a poor quality of the telescope obtained by putting an achromatic lens larger than the 60 mm lens of the Coronado II 60 mm (single lens?).

It is not enough to change the single lens lens with another achromatic (or apo) of the same focal ratio: the quality deteriorates considerably. If someone is happy with the result, it is because he does not have the experience to evaluate the significant loss of quality.
All this is easily verifiable. Take this project with three individual lenses similar to the Lunt with a single lens (for h-alpha).

http://www.telescope-optics.net/special ... scopes.htm

In my image 1) attached, you have its quality with the image points inside the diffraction. If you change the lens single lens with a perfect lens (or apo or achromatic: it is the same) of the same diameter and equal focal length you get a noticeable deterioration in quality (see image 2)).
If you then put a commercial achromatic lens 150 mm f /10 you get the bad results (see the image 3). It is Optics!
1) THREE SINGLE LENS_100 MM F_8.3.jpg
1) THREE SINGLE LENS_100 MM F_8.3.jpg (210.17 KiB) Viewed 1454 times
2) THREE SINGLE LENS_100 MM F_8.3_WITH REPLACEMENT OBJECTIVE.jpg
2) THREE SINGLE LENS_100 MM F_8.3_WITH REPLACEMENT OBJECTIVE.jpg (224.57 KiB) Viewed 1454 times
3) 150_F_10.jpg
3) 150_F_10.jpg (217.42 KiB) Viewed 1454 times

User avatar
Merlin66
Librarian
Librarian
Posts: 3137
Joined: Tue Dec 13, 2011 1:23 pm
Location: St Leonards, Australia
Contact:

Re: Lunt 60 mod options??

Post by Merlin66 » Wed Jan 17, 2018 7:59 am

If I understand your logic, the secondary lenses at the etalon assembly compensate for the SA in the singlet objective.
Using an achromat has “different “ SA resulting in over/under SA correction.
You may indeed be correct, but I have to say there are many PST mods which deliver very high quality results.
This may be due to the use of an achromat doublet in the PST.
"Astronomical Spectroscopy - The Final Frontier" - to boldly go where few amateurs have gone before
https://groups.yahoo.com/neo/groups/ast ... scopy/info
"Astronomical Spectroscopy for Amateurs" and
"Imaging Sunlight - using a digital spectroheliograph" - Springer

antonello
Ohhhhhh My!
Ohhhhhh My!
Posts: 63
Joined: Tue Mar 24, 2015 12:34 pm

Re: Lunt 60 mod options??

Post by antonello » Wed Jan 17, 2018 8:32 am

Yes, there is an achromatic objective in the PST and that is why in the PST it is possible to replace the small 40mm lens with a larger one. In this case the quality at the center of the field remains unchanged, as can easily be verified with an optical calculation program. If instead the lens objective of the solar telescope is single, it is not enough to put a larger diameter achromatic lens, even with the same ratio focal. In this case it is necessary to replace the two lenses of the collimator of the etalon ... that is, the negative lens in front of the etalon and the positive lens behind it. This can be done without too much difficulty with commercial lenses, one concave plane lens and a convex plano lens, placed exactly as I suggested in this topic.

viewtopic.php?f=10&t=15443&hilit=dream&start=75

An example of this solution (to use a commercial Lunt 35 etalon) is the one I have applied in an upgraded version of the Lunt 35. Now my Lunt 35 has become a Lunt 50... (with ZEISS 50/540 "teleminor achromatic lens" ).
In the following image you can see the quality.
Attachments
lunt_35_upgrade.jpg
lunt_35_upgrade.jpg (226.37 KiB) Viewed 1446 times
Last edited by antonello on Wed Jan 17, 2018 8:50 am, edited 1 time in total.

User avatar
Merlin66
Librarian
Librarian
Posts: 3137
Joined: Tue Dec 13, 2011 1:23 pm
Location: St Leonards, Australia
Contact:

Re: Lunt 60 mod options??

Post by Merlin66 » Wed Jan 17, 2018 8:46 am

I think you're saying for this specific set-up replacing the original negative (-159mm) and the rear positive (+204mm) in the etalon assembly to -300/+300 give an improvement in performance?
Is this correct?
"Astronomical Spectroscopy - The Final Frontier" - to boldly go where few amateurs have gone before
https://groups.yahoo.com/neo/groups/ast ... scopy/info
"Astronomical Spectroscopy for Amateurs" and
"Imaging Sunlight - using a digital spectroheliograph" - Springer

antonello
Ohhhhhh My!
Ohhhhhh My!
Posts: 63
Joined: Tue Mar 24, 2015 12:34 pm

Re: Lunt 60 mod options??

Post by antonello » Wed Jan 17, 2018 9:06 am

No, in this case I have taken the etalon of the Lunt 35 (which is frontal to the telescope and is not inside the telescope, as it is for the Lunt 50 and the Lunt 60). My modification consists in placing the etalon of the Lunt 35 inside a new telescope with a greater diameter than 35 mm (i have taken a 50 mm Zeiss). To make everything work I had to buy two new lenses to be used as a collimator in the Lunt 35 etalon.
Being the etalon of the Lunt 35, in original, in front of the lens, he does not have (by factory) the two lenses that are indispensable when the etalon is placed in the optical path of the lens (between the lens and its focus).

Of course, if in the Lunt 60 you change the lens with a larger diameter and use two long focal length lenses, to be put, as I have indicated, instead of the two original lenses in front and behind the etalon, it is possible to have the same lens quality of the big objective chosen ... All of this must first be verified with the optical calculation, but I have found that it is generally valid for objective telescope f/10.

User avatar
Merlin66
Librarian
Librarian
Posts: 3137
Joined: Tue Dec 13, 2011 1:23 pm
Location: St Leonards, Australia
Contact:

Re: Lunt 60 mod options??

Post by Merlin66 » Wed Jan 17, 2018 9:57 am

Understood.
I can see this requirement when you use an external etalon in a mod; you need to add the negative and positive lens...
What about modding the original smaller internal etalon assembly (which already has the negative/ positive in the assembly) to a larger aperture? Say, a Lunt 60 mod?
How do you/ can you calculate the "new negative/ positive" lens required?? I assume most modders use an achromatic objective for their mod......
"Astronomical Spectroscopy - The Final Frontier" - to boldly go where few amateurs have gone before
https://groups.yahoo.com/neo/groups/ast ... scopy/info
"Astronomical Spectroscopy for Amateurs" and
"Imaging Sunlight - using a digital spectroheliograph" - Springer

User avatar
Merlin66
Librarian
Librarian
Posts: 3137
Joined: Tue Dec 13, 2011 1:23 pm
Location: St Leonards, Australia
Contact:

Re: Lunt 60 mod options??

Post by Merlin66 » Fri Jan 19, 2018 12:26 am

Antonello,
Any comment????
"Astronomical Spectroscopy - The Final Frontier" - to boldly go where few amateurs have gone before
https://groups.yahoo.com/neo/groups/ast ... scopy/info
"Astronomical Spectroscopy for Amateurs" and
"Imaging Sunlight - using a digital spectroheliograph" - Springer

antonello
Ohhhhhh My!
Ohhhhhh My!
Posts: 63
Joined: Tue Mar 24, 2015 12:34 pm

Re: Lunt 60 mod options??

Post by antonello » Fri Jan 19, 2018 4:15 am

Sorry Merlin66, but I'm in bed from two days with a fever at 39 °... I hope to recover soon. Now I can not even reason...

User avatar
Merlin66
Librarian
Librarian
Posts: 3137
Joined: Tue Dec 13, 2011 1:23 pm
Location: St Leonards, Australia
Contact:

Re: Lunt 60 mod options??

Post by Merlin66 » Fri Jan 19, 2018 4:20 am

Sorry to hear that, mate....
I keep hearing Europe/ UK is blaming us for the "Aussie Flu" outbreak.....
When you're ready.
"Astronomical Spectroscopy - The Final Frontier" - to boldly go where few amateurs have gone before
https://groups.yahoo.com/neo/groups/ast ... scopy/info
"Astronomical Spectroscopy for Amateurs" and
"Imaging Sunlight - using a digital spectroheliograph" - Springer

antonello
Ohhhhhh My!
Ohhhhhh My!
Posts: 63
Joined: Tue Mar 24, 2015 12:34 pm

Re: Lunt 60 mod options??

Post by antonello » Tue Jan 23, 2018 8:26 am

The flu has passed ... but this time it was hard ...

Summarizing...

In solar telescopes with an achromatic lens, the lenses of etalon collimator system do not introduce spherical aberration and do not change the quality of the objective.
Precisely for this reason it is possible to replace the objective with a larger one, possibly with the same focal ratio, and obtain a new telescope with an image quality given by the larger lens.

In solar telescopes equipped with a single lens, the quality is determined by the set of three lenses: the objective and the 2 lenses of the collimator, appropriately calculated to cancel the spherical aberration.
In this case, in fact (see image),
lunt-60-schema_2.jpg
lunt-60-schema_2.jpg (192.45 KiB) Viewed 1282 times

the objective consists of a single negative lens which has a noticeable spherical negative aberration (sub-correction).
On the other hand, the two lenses of the collimator of the etalon have a positive spherical aberration, which compensates for that of the objective.
In this case, by replacing the single lens of the lens with a larger diameter achromatic lens, the telescope will show a strong positive spherical aberration (overcorrection) and will NOT be unusable.
This is what happens at the Lunt LS60 if you try to change the objective lens only.
To solve the problem, if you want to put a larger achromatic objective it is essential to replace both lenses of the collimator of the etalon, with two new lenses thath cancel the spherical aberration.
The simplest way to do this is to use a negative flat/concave lens in front of the etalon and a convex/plane positive lens after the etalon.
In this way a solar telescope is obtained without spherical aberration.

The same solution is usable if one has only the etalon. If you have only the etalon, just put the two lenses that I have suggested and you get a collimated etalon "universal" block, that is, that can be placed inside any commercial lens telescope
An example of this is my little modified Lunt 35.

lunt_35_mod_did.jpg
lunt_35_mod_did.jpg (1.25 MiB) Viewed 1296 times
In this case I have removed the 35 mm etalon from the original telescope and placed it between two lenses inside a small Zeiss 50/540 telescope. Now the Lunt can show all solar diameter in h-alpha, but with a quality that is much higher than the original.
The same work can be done for a larger etalon, for example 60 mm.
Last edited by antonello on Tue Jan 23, 2018 2:30 pm, edited 1 time in total.

User avatar
Merlin66
Librarian
Librarian
Posts: 3137
Joined: Tue Dec 13, 2011 1:23 pm
Location: St Leonards, Australia
Contact:

Re: Lunt 60 mod options??

Post by Merlin66 » Tue Jan 23, 2018 9:02 am

I appreciate your input and understand the Lunt 35 design.
What are the special lenses required for the Lunt 60 internal etalon????
"Astronomical Spectroscopy - The Final Frontier" - to boldly go where few amateurs have gone before
https://groups.yahoo.com/neo/groups/ast ... scopy/info
"Astronomical Spectroscopy for Amateurs" and
"Imaging Sunlight - using a digital spectroheliograph" - Springer

antonello
Ohhhhhh My!
Ohhhhhh My!
Posts: 63
Joined: Tue Mar 24, 2015 12:34 pm

Re: Lunt 60 mod options??

Post by antonello » Tue Jan 23, 2018 12:54 pm

The two lenses required for to upgraded the Lunt LS60 with a big achromatic objective are two simple catalog lenses (about € 25 each). Their simplicity and particularity is that put in that position and in that orientation (plane / concave and convex / plane) DO NOT introduce spherical aberration. If the Etalon of the LS60 Lunt is 35 mm large, the two lenses are the same as my modified Lunt 35 telescope ...
For an objective achromatic it is as if they were not there.

User avatar
Merlin66
Librarian
Librarian
Posts: 3137
Joined: Tue Dec 13, 2011 1:23 pm
Location: St Leonards, Australia
Contact:

Re: Lunt 60 mod options??

Post by Merlin66 » Tue Jan 23, 2018 12:59 pm

OK.
If the Lunt internal etalon is 30mm diam?
Bearing in mind the original negative/ positive lenses are available....
What performance improvement would you anticipate if the lenses are changed???
"Astronomical Spectroscopy - The Final Frontier" - to boldly go where few amateurs have gone before
https://groups.yahoo.com/neo/groups/ast ... scopy/info
"Astronomical Spectroscopy for Amateurs" and
"Imaging Sunlight - using a digital spectroheliograph" - Springer

antonello
Ohhhhhh My!
Ohhhhhh My!
Posts: 63
Joined: Tue Mar 24, 2015 12:34 pm

Re: Lunt 60 mod options??

Post by antonello » Tue Jan 23, 2018 1:58 pm

If the Lunt internal etalon is 30mm diameter... nothing changes

You can put two 30-40mm lenses with the same focal length of my Lunt 35 upgraded.

Sorry, but I'm not sure I understood your question correctly.
Here it is not a question of improving, but of maintaining the quality of the new objective. In my new Lunt (with the Lunt 35 etalon) I can put any objctive f: 10 or less with the certainty of a quality inside the Airy disk ...
The precise choice of focal lengths to be used in the etalon collimator also depends on the chosen objective .
For a 100 mm f: 10 lens (for example a TAL RS100 telescope), 2 lenses with focal -300 mm and +300 mm, are appropriate (better is -250 mm and +250mm, but they are not easy to find). In any case, if you have precise information on the new objective, I can calculate the most suitable value.

User avatar
Merlin66
Librarian
Librarian
Posts: 3137
Joined: Tue Dec 13, 2011 1:23 pm
Location: St Leonards, Australia
Contact:

Re: Lunt 60 mod options??

Post by Merlin66 » Tue Jan 23, 2018 8:55 pm

The conversation started when you said:
"" To have a good quality with another (bigger) objective, it is necessary to replace the negative and the positive lens of the etalon collimator...""

I was trying to establish exactly what replacement lenses were recommended for optimum performance in a Lunt 60 mod.
"Astronomical Spectroscopy - The Final Frontier" - to boldly go where few amateurs have gone before
https://groups.yahoo.com/neo/groups/ast ... scopy/info
"Astronomical Spectroscopy for Amateurs" and
"Imaging Sunlight - using a digital spectroheliograph" - Springer

antonello
Ohhhhhh My!
Ohhhhhh My!
Posts: 63
Joined: Tue Mar 24, 2015 12:34 pm

Re: Lunt 60 mod options??

Post by antonello » Tue Jan 23, 2018 10:59 pm

For me a good solution is an achromatic 100 mm f: 10 lens (as Tal rs100).
In this case (if the etalon of Lunt LS 60 is 30 mm in diameter) will be necessary to change the two original lenses of the etalon with a new pair of lenses of 30 mm in diameter and -250 mm and 250 mm of focal length (plano-concave and convex-plano lenses).
This change wil be radical and will make lose to the instrument its original purpose: to show the whole sun in H-alpha. With a new big objective this will no longer be possible, as there will be a reduction of the Seet Spot. With 100 mm f:10 objective, only a little over 5' of the Sun will be in h-alpha. Is it worth it?

antonello
Ohhhhhh My!
Ohhhhhh My!
Posts: 63
Joined: Tue Mar 24, 2015 12:34 pm

Re: Lunt 60 mod options??

Post by antonello » Thu Jan 25, 2018 8:12 am

Hello Merlin 66
I managed to do two small projects to be able to use the Lunt LS60 etalon with achromatic objectives.
Both have two collimation lenses 30 mm diameter and -250 and +250 mm of focal. These lenses is it available in the Optosigma catalog at 25 $ each ...)
The first project involves the use of a 50/540 objective (type zeiss teleminor), with a 0.5 ° field angle. All information is in red in the figure. This allows you to keep the possibility of observing all the sun in h-alpha.
Changing only the objective (nothing else) it is possible to have a higher resolving power.
In the second project It has been planned a objective 100/1000 = (type tal RS100)
In this case the field in which the rays enter the etalon with an angle of +/- 0.5 ° is about 12 '.
Obviously you can also put a objective with larger diameter, but there might be vignetting. In my 2 projects (and with the 250 mm focal length lenses there is no vignetting).
I hope everything is clear.
50_540.jpg
50_540.jpg (990.75 KiB) Viewed 1240 times
100_1000.jpg
100_1000.jpg (946.51 KiB) Viewed 1240 times

Macavity
Oh, I get it now!
Oh, I get it now!
Posts: 29
Joined: Tue Mar 15, 2016 11:45 am

Re: Lunt 60 mod options??

Post by Macavity » Sat Mar 24, 2018 9:34 am

Some very useful (hard) information! Do you have similar data re. the
standard Lunt 50 (pressure tuner)? I have to admit I now wonder if
*abandoning* my 80mm ED Frankenscope project would be better... :P

Originally based on a "stopped down" ST120 achromat, I sense (hope!)
the ED80 objective will still be a BIT better! (Testing it on SUNday?) :D
As a "random number" objective Strehl values are 0.7(?!?) & 0.95 resp.

With my 1/3" Chameleon Cam, the native Lunt50 (just!) shows a full
disk. The f/7.5 (600mm) ED objective gives a "rather horrible" image
but seems to work "better" when Barlowed to (effective) f=1200mm. ;)

I suppose the WORTH of any upgrade (from a single stack Lunt 50) has
to be judged against the (un)likelihood of being able to *afford* much
better... But a dose of *reality* is genuinely useful and educational! :cool:

Post Reply

Who is online

Users browsing this forum: No registered users and 2 guests