Show me your lunt solar mods

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SPACEBOY
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Show me your lunt solar mods

Post by SPACEBOY » Mon Oct 09, 2017 6:19 pm

Hi All

I'm new to solar chat but have been solar observing for the past 3-4 years with various filters and scopes. I currently have a project planned to mod my LS60tha with an OMNI XLT120. The plan is after chopping the OTA to the desired length and to remove the focuser and have an adapter to allow the lunt etalon assembly, focuser etc to attach directly to the OTA focuser reducer. Up the objective end the hope is to have a 3D printed cell holding a 110mm Baader D-ERF internally mounted.

There seems to be plentiful PST mods around but few lunt. I can understand the reasoning as PST are considerably cheaper to purchase and there are extensive guides on how to mod them but I am aware that there are some Lunt mods knocking about to which I hope to add my own with a little help and guidance from members on this forum. If anyone knows of a machinist in the west Midlands area able to make a reducer for the focuser this would also be handy.

So in the hope to gain some inspiration and also some ideas on how to mod a Lunt I'd be grateful for any pics members have or know of consisting a Lunt solar mod. Also on another note does anyone know of any difficulties encountered splitting the etalon from the white objective tube on Lunts?

Thanks in advance

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marktownley
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Re: Show me your lunt solar mods

Post by marktownley » Mon Oct 09, 2017 6:52 pm

I think there's a few people know who've done a variant with different scopes on what you're wanting to do so there will be plenty of info on here. You should be able to 3D print a reducer for your focuser, just go for a dense fill. Where abouts in the west midlands are you?
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Solar images, a collection of all the most up to date live solar data on the web, imaging & processing tutorials - please take a look!

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Re: Show me your lunt solar mods

Post by SPACEBOY » Mon Oct 09, 2017 7:09 pm

Hi Mark

I'm up the road from you and not far from Halesowen. I have planned to have the ERF cell printed as it can save on material and lathe time along with it being black but I'd rather go with ali for the focuser adapter for piece of mind if nothing else. I could in all fairness probably do the bulk of the turning on the adapter myself but I have absolutely no experience cutting threads and I hear the lunt is a 1mm fine thread which will be testing for even those who know what they are doing.

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marktownley
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Re: Show me your lunt solar mods

Post by marktownley » Mon Oct 09, 2017 8:08 pm

Should be a pretty straight forward mod. Let me know if you find anywhere local to mill the ali.

Mark
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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!

SPACEBOY
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Re: Show me your lunt solar mods

Post by SPACEBOY » Wed Oct 11, 2017 4:20 pm

Will do Mark.

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GreatAttractor
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Re: Show me your lunt solar mods

Post by GreatAttractor » Thu Oct 12, 2017 5:23 pm

Here's mine, works very well: viewtopic.php?f=9&t=19238
Most of my solar images since then have been captured with this setup.
My software:
Stackistry — an open-source cross-platform image stacker
ImPPG — stack post-processing and animation alignment
My images

SW Mak-Cass 127, ATM Hα scope (D=90 mm, LS50 etalon), Lunt LS50THa, ATM SSM, ATM Newt 300/1500 mm, PGR Chameleon 3 mono (ICX445)

Macavity
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Re: Show me your lunt solar mods

Post by Macavity » Sat Oct 14, 2017 2:12 am

I have added a few practical details re. the making of my Lunt50 / SW ST120
86mm Frankenscope now. I acknowledge the ideas & encouragement of others! :)

viewtopic.php?f=9&t=23187

No skilled machinist *immediately* on hand here either. But sometimes easier
to make a "prototype" to get the "Engineering Drawing" into acceptable form? ;)

Chris / Macavity (SGL)

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Re: Show me your lunt solar mods

Post by SPACEBOY » Sun Oct 15, 2017 5:10 pm

I had originally planned to go with a 110mm Baader d-erf thinking this is going to keep the filter no further than the recommended 1/3 the way down from the objective but now I actually have the donor scope I found the internal dimension of the omni120 to be only 113mm.

Even with a risky 1mm catch on a cell this means a 110 mm erf is going to be too large.

Are there any other erf as highly regarded as the Baader D-ERF which offer sizes around 100mm ??

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Re: Show me your lunt solar mods

Post by Macavity » Mon Oct 16, 2017 9:06 am

Hi SB! :)

There is e.g. a convenient EU source of 100mm Lunt ERF's at Teleskope Service (DE)?
https://www.teleskop-express.de/shop/pr ... ilter.html

There is a slight "flaring" of the ST120 lens cell to give a canonical 120mm.
But the internal diameter of the ST120 OTA is indeed about 112mm too! :|

However, this being my *first ever* Frankenscope, I decided to "stick with the rules" in the design. Since I was upgrading the Lunt 50 *BF600* version, I decided to go with a f=600mm Donor scope. You can calculate light cone width at the blocking filter, but I decided to stay within the quoted limits! That limit fixed, I followed the general advice to stick with the Lunt f/7 light cone. Solar scopes use lenses to paralellise then restore this before / after passing it (parallel) through the Etalon etc. This also fixes things to f/7 and an objective aperture to 86mm! Ergo my 90mm Baader ERF. :)

Whatever the *individual* experience, it is anecdotal that mounting the ERF internally may give rise to tube currents? But simply it is *easier* to mount the thing on the front of the scope! lol. You may sacrifice some (potential) aperture, but I also checked out the (Ronchi Tested!) *optical* performance of Bresser / Skywatcher Achromats. I looks like they work best in green light and may suffer some spherical aberration at H-Alpha wavelength? :shock:

I tried a few ad-hoc tests of my ST120 and concluded the performance of the objective WAS better using a (green) Solar Continuum than a (red) standard H-Alpha (nighttime) filter. It is (as ever) far easier to focus a white light scope using a GREEN filter! But stopping down a faster objective down a bit from full aperture would not hurt things? I decided to be content with an externally mounted ERF - An 86mm H-Alpha seemed a FAIR upgrade! :cool:

It is not a *Full Disk* Solar scope. I checked that out too... Vignetting, non-uniformity of tuning (sweet spot) limits it. BUT it does give some encouraging *Barlowed* images. Overall I am pleased and excited by the result of this. On my limited budget, it is all totally FINE by me! I have some vague notions of upgrades. A BF1200 + greater aperture? Use the ERF inside the tube? Like Dogs and CATS, an ERF is "for life"! :mrgreen:

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Re: Show me your lunt solar mods

Post by SPACEBOY » Mon Oct 16, 2017 12:43 pm

Hi Macavity

I had either a daystar or Lunt erf in a PST / TAL stage 1. It is my understanding and indeed experience that the DS or lunt offerings are absorption filters and so let some heat through where as the D-erf from Baader is said to reduce this even further as it reflects a large part of the energy back out of the objective. While the DS and lunt are perfectly safe and affordable they do though on the hotter days suffer from a build up of thermals in the OTA . I'm sure the Baader will suffer a similar fate to some degree due to it being internally mounted but my hope is because it is a true rejection filter any thermals will be kept to a minimum. If I can keep it far enough up the OTA that is.

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