Put a Lunt LS40 Etalon etc on another telescope? or How to get a decent focuser.

[Alan White]

Hi All, I am after experienced Solar nuts to assist please, this is a very specific question.

I have a Lunt LS40 Ha scope, I get good results, but the helical focuser is utter rubbish.
Its been back and the helical focuser replace 3x by the vendor,
I the upgraded to the FT focuser and had a run of challenges here too, one arrived in a bag and smashed,
the second arrived and had neither a Feather or Heavier touch as it was jammed solid, apparently caused by grease, it went back.
Its back with a helical and works fine, but that helical is a very fragile and I wait for the next issue.

So I am pondering shifting the Etalon unit and the blocking filter to a small telescope of decent quality and focuser, but this is where I step into unknown territory...
Has anyone else done this or am I off reservation?

 

Edited June 15 by Alan White

[NGC 1502]

Hi Alan, this may or may not be relevant…..however if I did the same as you are contemplating-

With my Lunt 35HA, it has a 2 element objective.  If the front etalon is removed, that leaves the 2 element objective with a 400mm focal length at the front end of the optical tube. This may not matter of course, if the new refractor has the same focal length as the original.

BTW, the helical focuser on my Lunt 35 is integral with the blocking filter and works fine. Shame yours does not even after multiple replacements.

I’m thinking that you may be better off if you attempt (yet again) to sort your focuser.

All the best, whatever you try.

Edit…ok having posted the above, it may be complete DRIVEL!  If your donor refractor has a different focal length it may not matter a jot, focus should be achieved without issue. There does remain something else. If I tried the same with my Lunt 35, the tilt tuner is a small and flexible metal plate between the etalon cell and optical tube, with a screw adjuster on the opposite side.

 

Edited June 11 by NGC 1502

[Alan White]

Thanks Ed

I too wonder about the helical, I tried to find a better replacement, but nothing looks to match up
perhaps that is another avenue for collective advice

 

Edited June 12 by Alan White

[NGC 1502]

Hi Alan, please see the edit on my previous post…

[Alan White]

I hope I have found my solution, I will feedback to the SGL community when I have it.
No new scope just a well made helical focuser without the sag and slop of the dire Lunt one.
Its made in Italy, web site once translated makes sense.

https://www.adrianololli.com/articolo.asp?ID=6117

The above image is from across the pond on CN and shows one fitted to an LS40,
the unit is sold for the LS50, but as the same thread, fits either.

This I hope will make a nice scope, that performs well, into a very nice scope that is a pleasure to use.
Watch this space...

 

[Alan White]

I have had a message from Adriano Lolli, order is confirmed and delivery is expected in 3-4 weeks time as order levels are up.
Happy with that.
Patience, I hope, will be rewarded.

Edited June 15 by Alan White

[Owmuchonomy]

I don't know why Lunt persist with the helical focuser.  It is dreadful.  Fortunately I have a FT upgrade on my Lunt. (I now have the 80).

[michael8554]

It's years since I sold my transplanted Meade PST, but back then it was essential that the new scope be f/10.

Maybe the Lunt has to be the same ?

Michael

[vlaiv]

6 minutes ago, michael8554 said:

It's years since I sold my transplanted Meade PST, but back then it was essential that the new scope be f/10.

Maybe the Lunt has to be the same ?

Michael

If I'm not mistaken, Lunt 40 has front mounted etalon while PST has etalon in that unit at the back together with blocking filter and diagonal - the thing that gets transplanted to larger scope.

With front mounted etalon - you don't really care how fast the optics behind it is - because etalon is working in collimated beam that arrives at aperture. With rear mounted etalon - its working in converging beam and it's optimized for some angle of convergence (it actually has diverging lens that makes beam collimated again and then another converging lens behind the etalon - again, if I'm not mistaken).

[Peter Drew]

47 minutes ago, vlaiv said:

If I'm not mistaken, Lunt 40 has front mounted etalon while PST has etalon in that unit at the back together with blocking filter and diagonal - the thing that gets transplanted to larger scope.

With front mounted etalon - you don't really care how fast the optics behind it is - because etalon is working in collimated beam that arrives at aperture. With rear mounted etalon - its working in converging beam and it's optimized for some angle of convergence (it actually has diverging lens that makes beam collimated again and then another converging lens behind the etalon - again, if I'm not mistaken).

You are correct.     🙂

[Alan White]

Lunt LS 40 is a front mounted etalon and rear blocking filter.

Edited June 16 by Alan White

[Rusted]

Lunt's Pressure Tuned etalons, in the rear light path, are meant to enjoy f/7 converging light cones.

The popular 150mm f/8s are still useful for H-a mods. Provided they are given a front D-ERF for heat protection of the "innards."

The f/10 stipulation holds true for the PST etalon.

[vlaiv]

1 hour ago, Rusted said:

Lunt's Pressure Tuned etalons, in the rear light path, are meant to enjoy f/7 converging light cones.

Indeed - their 60mm "all around" scope is actually 70mm F/6 ED doublet - but it has been stopped down to 60mm to provide F/7 cone to their 40mm internal etalon.

I supposed one could move etalon to larger scope - but I haven't seen it done. It is indeed possibility?

[Rusted]

I used my Lunt 60MT etalon in my iStar 150 f/10 mod with success. Used with a 2x "Shorty" Barlow.
A great improvement on the PST etalon. The larger aperture of the Lunt etalon provided a much larger sweet spot than the PST.
It also remained stable. Without the constant need for adjustment and re-tuning of the PST etalon.

The Lunt PT etalons don't readily lend themselves to changing their collimation lenses.
Since they must tolerate the pressure changes without leakage.
Changing these lenses would allow more variation of objective f/ratio.
Not a job for the hamfisted. If it is even possible.

[Rusted]

[Jforson]

8 hours ago, Alan White said:

Lunt LS 40 is a front mounted etalon and rear blocking filter.

Hi Alan, 

last week I took delivery of a lunt 40mm.  Just a quick question, what case have you used for storing the scope?

I am pretty lucky as my focuser is fine, not as nice as the one on my TV-60 but fine for visual.  
 

 

[Alan White]

The case was a foam lined one and I cut the insert out, very carefully with a carving knife

Case came from Maplin online.

 

Lucky you on the focuser

 

Edited June 17 by Alan White