10 replies to this topic

[Jethro777]

I would like to try and connect a 2" eyepiece to a refractor with a 36.4mm thread.  

I can already do this - but with a 1.25" eyepiece with this adaptor (Baader #2408195), is there a way to do this also with 2" eyepieces?

[ngc7319_20]

Maybe these folks could make a custom one for you?

 

www.preciseparts.com

[Astrojensen]

You'll get severe vignetting, so the field won't be much larger than what's possible with 1.25", in case you didn't know. 

 

What exact scope are you trying to convert?

 

 

Clear skies!

Thomas, Denmark

[markb]

Thomas is of course correct.

 

It can be done with a 36.4 to T2 thread adapter, and then attaching a T2 diagonal (Baader is the obvious, but expensive, one) or a T2 to 2" visual back, AgenaAstro has the bluefireball one. No need to empty your bank account for preciseparts.

 

But, as Thomas points out, the tiny refractor focuser tube will choke the light path and limit the field. I've never tried it so I cannot estimate the degree of vignetting. Long refractor tubes on old classics will accentuate the problem. I have done the 30.6 to T2 to 1.25 conversion without obvious problems, mentioned only if that gives you any usable information.

Edited by markb, 02 December 2020 - 01:28 PM.

[Littlegreenman]

You'll get severe vignetting, so the field won't be much larger than what's possible with 1.25", in case you didn't know. 

 

What exact scope are you trying to convert?

 

 

Clear skies!

Thomas, Denmark

Vixen made and still makes tubes from 40mm? 50mm? up to 150mm.

The drawtubes generally are threaded and different visual backs (eyepiece holder) can be used, or adapters to attach a camera. The diameter of the drawtube and threads vary, even with similar sized scopes. 

You may or may not get severe vignetting, depending on on the exact scope.

Many of the fluorite and ED scopes, for example have 58mm, 50mm, or 52mm diameter drawtubes, and were sold with a 2" fitting. It is just a matter of finding the right Vixen adapter. That may be the biggest challenge.

I'm ignorant if say, the Firstscope 80, an 80mm f/11 will suffer vignetting if converted to 2".

So, we are back to what is the exact model you have, and the diameter of the draw tube.
 

[Jethro777]

Hmm, well, it is an older 80mm f/15..

I wanted to put a Masuyama on it, where the outer edge is soft anyway..

Edited by Jethro777, 02 December 2020 - 02:18 PM.

[Astrojensen]

Hmm, well, it is an older 80mm f/15..

I wanted to put a Masuyama on it, where the outer edge is soft anyway..

The thing is, the Masuyama might not be so soft around the edges at f/15... 

 

But if the field stop is considerably larger than, say, 30mm, you won't see the edges at all... The 32mm Masuyama will be stopped down to an AFOV of ~50°, the 26mm will have ~70°. The 20mm will be almost full field, at around 80°. 

 

 

Clear skies!

Thomas, Denmark

[SeattleScott]

At F15 the light cone isn’t shrinking that fast so something with 32-33mm field stop might work just fine.

[25585]

You need Vixen parts 77292 EA 42 to 50.8mm and 72953 DC ring 43 to 36.4mm.

[Jethro777]

You need Vixen parts 77292 EA 42 to 50.8mm and 72953 DC ring 43 to 36.4mm.

 

Well, I think I will go with the Baader version of that.

Baader Parts: #1508039 and #2956242

 

So, given all that, which Masuyama would work well? 

[Terra Nova]

You can create a 1.25” to 2” hybrid diagonal using a Baader T-2 Prism star diagonal body (they sell everything modular). Get the one with the oversized 32mm prism. Then get the 1.25” nosepiece with the male T-2 back. This threads into the Baader prism body and is available from Baader and also Blue Fireball (Agena Astro). Last, get the Baader T-2 2” eyepiece holder. Once assembled, just plug it into your 36.4mm to 1.25” threaded Vixen visual back. You will be out quite a bit for the parts but you will have lots of expandability with the Baader prism body. For instance, you can get 0.965” and 2” to T-2 nosepieces, and 1.25” and 0.965” eyepiece holders for many different combinations.