The Charlie Bates Solar Astronomy Project is proudly sponsored by the following fine companies:
ImageImageImageImage
Image
Image
Solar Analemma. This outstanding image from Alexandra Hart taken over a period of 4 years charts the midday position of the sun in the sky throughout the year. The north–south component of the analemma results from the change in the Sun's declination due to the tilt of Earth's axis of rotation. The east–west component results from the nonuniform rate of change of the Sun's right ascension, governed by combined effects of Earth's axial tilt and orbital eccentricity.

Merry Christmas, Happy New Year and looking forward to a great solar cycle 25!

Welcome to Solar Chat! The best forum for Solar Astronomy
Moving forward from solar cycle 24 to 25

No adapters, no tube cutting: the easiest 80mm "stage 1" Lunt LS50 mod possible!

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
User avatar
Roel80
The Sun?
The Sun?
Posts: 16
Joined: Sat Nov 23, 2019 8:25 am

No adapters, no tube cutting: the easiest 80mm "stage 1" Lunt LS50 mod possible!

Post by Roel80 » Mon Dec 23, 2019 2:38 pm

I recently bought a Visionking 80mm f/7,5 refractor on Ebay to use it as a donor scope to mod a Lunt LS50 to an 80mm h-alpha scope. It's a Chinese, but very well made telescope with a retractable dewshield, 1:10 Crayford focuser, tube rings and dovetail plate included. It even comes with some kind of sports bag (low quality, but still).

When the refractor arrived a few days ago, I started to measure things, to determine whether I had to cut the tube and/or make an adapter to mount the Lunt's etalon unit at the "magic" distance from the focal plane.
I discovered that when you remove the focuser, the remaining mounting ring has an internal diameter of 70mm. That's quite convenient, because the etalon unit has M68 male thread, and will fit snugly when a 1mm thick strip of plastic (or tape, or whatever material available) is placed around the piece of thread. Just tighten it with the three allen screws in the ring, and it looks like the two are made for eachother. A one minute job: nice!

But that was not the only surprise. It turned out the ring places the etalon unit at the exact same distance (-168mm) from the focal plane as the original 50mm Lunt OTA. And I mean EXACT! I double checked by measuring again, and by switching between the original OTA and the 80mm OTA, and I didn't have to adjust the focuser AT ALL for a sharp image. I mean, this is incredible, right?

All I basically had to do, is mount an ERF (inside the tube, for it is a 75mm), and that's it!
With this refractor you can basically built a 'stage'1' 80mm Lunt mod it the time it takes to mount an ERF. It even looks great:
DSC_2333.jpg
DSC_2333.jpg (321.17 KiB) Viewed 297 times
DSC_2336.jpg
DSC_2336.jpg (111.85 KiB) Viewed 297 times
DSC_2335.jpg
DSC_2335.jpg (130.12 KiB) Viewed 297 times
DSC_2334.jpg
DSC_2334.jpg (182.24 KiB) Viewed 297 times
Last edited by Roel80 on Mon Dec 23, 2019 2:57 pm, edited 1 time in total.

User avatar
Roel80
The Sun?
The Sun?
Posts: 16
Joined: Sat Nov 23, 2019 8:25 am

Re: No adapters, no tube cutting: the easiest 80mm "stage 1" Lunt LS50 mod possible!

Post by Roel80 » Mon Dec 23, 2019 2:49 pm

But there is more! If you would like to replace the original helical focuser, it's possible to use the Visionking's 1:10 Crayford, although the drawtube needs to be shortened and an adapter will be needed to mount in onto the back side of the etalon unit. The focusing part is even shorter than the helical focuser and a travel of 12mm is possible when you cut the drawtube. It is way cheaper to use the Visionking's focuser with a custom made adapter than buy a $$$$$$ Feathertouch.


DSC_2338.jpg
DSC_2338.jpg (179.7 KiB) Viewed 296 times
DSC_2339.jpg
DSC_2339.jpg (170.28 KiB) Viewed 296 times


This is something I'm planning to do in the weeks to come. To be continued!

The Visionking refractor is easy to find for around US$200 when you search for "Visionking 80mm" on Ebay.

User avatar
marktownley
Librarian
Librarian
Posts: 26656
Joined: Tue Oct 18, 2011 5:27 pm
Location: Brierley Hills, UK
Contact:

Re: No adapters, no tube cutting: the easiest 80mm "stage 1" Lunt LS50 mod possible!

Post by marktownley » Mon Dec 23, 2019 5:14 pm

Very nice!
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!

Marcus444
Oh, I get it now!
Oh, I get it now!
Posts: 22
Joined: Sat Sep 12, 2015 5:11 pm

Re: No adapters, no tube cutting: the easiest 80mm "stage 1" Lunt LS50 mod possible!

Post by Marcus444 » Tue Dec 24, 2019 12:45 pm

Looks fantastic - do report back on how it performs.
Lunt LS60THa, 60FHa
Quark Chromosphere
Baader Herschel wedge
Tak FC-100, TV85

Marcus444
Oh, I get it now!
Oh, I get it now!
Posts: 22
Joined: Sat Sep 12, 2015 5:11 pm

Re: No adapters, no tube cutting: the easiest 80mm "stage 1" Lunt LS50 mod possible!

Post by Marcus444 » Tue Dec 24, 2019 12:58 pm

Notice there was a report of a similar mod on solarchat back in July 2017 - some alignment issues and keyhole effect, but obviously improvement in detail
Lunt LS60THa, 60FHa
Quark Chromosphere
Baader Herschel wedge
Tak FC-100, TV85

User avatar
MalVeauX
Almost There...
Almost There...
Posts: 1100
Joined: Tue May 09, 2017 7:58 pm
Location: Florida

Re: No adapters, no tube cutting: the easiest 80mm "stage 1" Lunt LS50 mod possible!

Post by MalVeauX » Fri Jan 10, 2020 2:19 pm

Looks nice, any images or opinion on performance? Potential to double-stack? Transmission?

Very best,

User avatar
Roel80
The Sun?
The Sun?
Posts: 16
Joined: Sat Nov 23, 2019 8:25 am

Re: No adapters, no tube cutting: the easiest 80mm "stage 1" Lunt LS50 mod possible!

Post by Roel80 » Sun Jan 12, 2020 3:06 pm

Thanks!

Well, I intend to use the telescope for visual observations only, so unfortunately I can't show any images.. All I can say (with the Sun barely 15 degrees altitude at noon these days) is that it works like a charm! I got some great details in small proms some weeks ago. Surface details are nice, detailed, and contrasty. The B600 in combination with the faster f/ gives me a significant wider true field of view compared to my old 70mm PST mod with its BF5.
The sweet spot is fairly large, round and centered, so everything appears to be in line. And that's without one bit of machining!

The mount I use is from my 3" Polarex/Unitron refractor


DSC_2350.jpg
DSC_2350.jpg (482 KiB) Viewed 114 times

User avatar
marktownley
Librarian
Librarian
Posts: 26656
Joined: Tue Oct 18, 2011 5:27 pm
Location: Brierley Hills, UK
Contact:

Re: No adapters, no tube cutting: the easiest 80mm "stage 1" Lunt LS50 mod possible!

Post by marktownley » Mon Jan 13, 2020 2:32 pm

Nice setup!
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!

Post Reply