DIY Lunt 50THa MOD

[astro1965]

Hi all,relatively new to solar observing and have just recently purchased
a lunt 50mm scope.Have been enjoying using it and still trying to get the
best out of the scope.Would probably like to do a mod using a 120mm f5 refractor or possibly a 80mm f5.Would one of these be suitable to use with the Lunt 50mm f7 scope that I have?
Does anybody know of a good site with detailed instructions
on how to go about modifying this particular scope?Have been to the solar chat forums,but there seems to be so much info there,its all a bit too much for me.Thanks all,Nick.

[traveller]

Trying messaging Ken (Merlin66).
:)

[Star Catcher]

Hi Nick

I am using a 127mm F7.5 refractor with a Lunt DSII unit and Quark etalon in this way. I am however not an expert at mods and you can direct your query to the best solar imaging resource on the net here: https://solarchatforum.com/index.php

In my opinion it would be far simpler using a Quark Chromosphere etalon eyepiece rather than doing the mod you suggest. It would however be more expensive! You would get away with not having an expensive ERF at the front of your 120mm refractor, something which would be essential if you tried using your Lunt's etalon. You would simply use an UV/IR blocker in your diagonal and then use the QUARK.

It is possible to do your mod but you would need to protect the Lunt's internal etalon unless you have an externally mounted etalon version. The protection would have to come from a full front 120mm ERF which is fairly pricey. Also the position of the etalon may require the tube to be modified in its length. You would also have to get the scope's focal length up to at least F20-F30 using a telecentric barlow.

Hope that helps.

Ted

[astro1965]

Ted are you using a quark,the ones that fit into the diagonal and you then simply put an eyepiece in and observe?If so,how do you find it?

[Star Catcher]

Yes I use the quark in my 127mm in SS mode. When I want a more narrow bandpass I add the DSII unit and use the scope in double stack mode.

The quark I have gives superb prominence views and reasonable surface details. It is the prominence version. You can also get the chromosphere version with narrower bandpass and more surface details. This is the one most people get. I wanted the wider bandpass to observe faint prominences.

Quarks are a great when you get a good one. In the solar imaging community there are many stories of people sending back units because they disappoint. I had the same experience. I suspect those who do imaging will be more fussy than those who do visual.

The Quark is a great idea and turns any refractor up to 120mm into a solar scope. You do have to add a UV/IR blocker to reduce the heat load on the quark when operating with 120mm aperture.

Ted

[Merlin66]

Nick,
A few comments:
The success of a mod, based on my ten years experience, is directly related to the quality of the etalon used.

The 10/80/10 rule seems to apply to all the etalons I've seen.
10% are basically rubbish and should never have left the factory.
80% are OK but....just acceptable performance - sometimes soft surface detail and loss of clarity on the proms.
10% are Whooooo -that's neat!!!!
If you use an average etalon in a mod you will not get the bang per buck - spending the $$$ to get the OTA/ ERF and larger blocking filter will just get you a brighter average etalon performance.

The Lunt mod involves removing the front objective and either using the remaining tube as an adaptor to the donor or making up a suitable adaptor to hold the etalon assembly/ focuser in the donor OTA.
Either way the etalon will act as an aperture stop and give an f7 outcome.
The scopes you mention, 120/600 and 80/400 would end up 85/600 and 57/400 systems.
Above an aperture of 60mm I strongly recommend either a full aperture ERF - the Baader D-ERF is excellent, or at least an internal ERF of >50% the aperture.
The blocking filter? I assume you have the basic B400? This will cause vignetting with focal lengths >400mm. For a "good" mod you'll need something like the B1200.

All this adds up $$$$$$
Doing a mod is not a trivial investment, and will probably not allow you to do full disk imaging. Think it through carefully.

[astro1965]

Thanks Ken for that useful info,I was told your the man I should seek out for help.I am only a visual observer and do no imaging.I don't mind not seeing the full disk when observing.
I was thinking of placing a 75mm erf internally.What do you think of the Lunt 75mm ERF energy rejection filter and using a baader uv/ir filter in the nosepiece of the lunt diagonal?
I am not sure of the exact placement of the ERF filter internally?Would this internal filter further reduce the effective aperture of the resulting scope?
Also would l be able to use a pair of burgess binoviewers I have with the resulting scope,as I would be able to adjust the placement of the Lunt adaptor in the 120mm scope and thus allowing me to achieve focus by moving it up or down?
Thank you Ken,…..Nick.

[04Stefan07]

Was going to say the same as someone else here, message Ken he's a legend on anything solar. Very resourceful.

Great tekescope purchase by the way. I got the Lunt LS50THa too.

If you want a really good case for it send me a PM, there's a place in Melbourne who I purchased it off.

[Merlin66]

Nick,
OK let's see if I can help....
1. The Lunt ERF is OK but not as good as the Baader.
2. The position should be less than 50% of the focal length behind the objective.
3. The UV-IR is good.
4.If you can use the bino viewer with the basic Lunt 50 then yes you can still use them after the mod. The mod (if done correctly) WILL NOT CHANGE the backfocus available. The position of the etalon assembly is FIXED relative to the objective - think about it - all you're doing is replacing the existing OTA with another - the etalon assembly in the original scope doesn't move, just the focuser behind it.

[astro1965]

Thanks to everyone who replied.Well it sounds like there is quiet a fair bit of work involved in modifying a solar scope to suit one's taste,so for the time been,I think I will enjoy and use the scope as it is.If my interest in solar observation continues,then I might consider a mod down the track.
I am just waiting for Siebert optics to start taking orders again and will purchase a 1.2X OCA for using on binoviewers and the Lunt 50mm.
Should be interesting to see the views.Thanks everyone,Nick.