6 inch f15 Refractor Self-build: Light Shroud as Tube?

[spearbearer]

Hi -

 Within the next few months I am about to start building a 6 inch f15 refractor, having already in my possession the required achromatic objective which I purchased from iStar optics. It cost more than most introductory level scopes do so I have to make a serious go of it. It is, of course, a beautiful lump of glass

I am pondering various options for the tube (which will be some seven and a half feet long). On looking through the literature I find various options which I am weighing up, but when it comes to refractors there seems to be very little on the use of a black fabric light shroud stretched over a frame, such as is quite common on larger Dobsonians.

Unless there is a reason not to, I'm quite tempted to go down this road for reasons of both simplicity and low weight. I'm also thinking that aesthetically it might look pretty cool too if it's done right. I understand that the frame would have to be pretty sturdy to compensate for the lack of structural support from the exterior cladding.

Any advice/ideas about this question will be most welcome.

Also, any ATM's out there with any suggestions on other aspects of such a build - please feel free to comment!

Looking forward to your thoughts...

gary

[Chris]

Now this is right up my street! I'll be following your progress on this with interest, Gary  

If you check out page 68 on the "show me your frac" thread, there is a lovely DIY skeleton framed refractor pictured a few posts down. Maybe it's owner @PaulC-I can offer some words of wisdom?

 

[spearbearer]

Chris -

Wow, yes - that looks very nice, and it encourages me. I will  message Paul in the near future.

Very pleased that you will be following my build, but I suspect that the timeframe will be glacial and I have a couple of other projects to complete before I even start.

This thread seems like as good a place to log it as any though!

Much appreciated; thanks.

gary

[Chris]

Glacial? don't worry about glacial... you should see how slow my mirror grinding thread is going  

 

[Peter Drew]

Hello Gary. I've built quite a number of 6" and 8" refractors professionally over the years and currently own a self built 8.5" F12 achro, 6" F10 achro (solar telescope) and a 5" F15 APO triplet. The 8.5" was made by joining two 8" F6 Newtonian tubes. Istar do a framework refractor that would be worth a look at. I will also be following your progress with interest.  

[spearbearer]

Chris - I can imagine! That seems to be the nature of mirror grinding .

Will look at your thread to see.

[spearbearer]

Hi Peter -

Wow! Some serious scopes you have built. Can they be seen on SGL or elsewhere online?

Will certainly check out iStar's framework refractor. That should be interesting.

Many thanks,

gary

[John]

Thats going to be some scope Gary

I used to have an Istar 6" F/12 in the Istar solid tube. Very long and very heavy. Mounting the thing was the big challenge - cost as much as the scope !

Istar use a framework tube for their TCR refractors. Here is some stuff about it on the Istar Scope Club forum:

http://istarscopeclub.proboards.com/thread/318

It's quite a lot lighter than a solid tube and uses an internal baffled section for the light path immediately in front of the focuser.

 

[johnfosteruk]

Another follower here  Gary. I hope the build goes well.

[spearbearer]

 Peter -

Ohhh yes. The iStar Perseus TCR 150-12 does indeed look amazing...

The immaculate CNC milled tube rings and general finish are beyond my reach, but finding other ways is part of the fun!

So far, since starting this thread, I have heard nothing to dissuade me from the open frame with light shroud approach...

[spearbearer]

Johnfosteruk -

Thank you. It will take time... but your interest is appreciated.

Nice inventory you have there, by the way

[spearbearer]

John (Perfectly Normal Beast) -

I'll worry about the mounting issues once I get the scope made :-)

That iStar open frame job is a thing of beauty...

Thanks for the pointer.

[John]

This was one of the mounting arrangements that I used. EQ6 + Meade Giant Field Tripod (3 inch steel legs !). The whole lot weighed over 100 lbs so it was not "grab and go"

 

 

[spearbearer]

Indeed - 'grab'n'go' isn't on the agenda with this scope!

I am due to build a pier out of ductile iron pipe on which I hope to be able to mount a few different telescopes in time.

For the scope in question, I envisage an alt-az that I can swing around - perhaps according to Richard Berry's original design, or similar.

Nice scope and mount in the picture...

[johnfosteruk]

26 minutes ago, spearbearer said:

Johnfosteruk -

Thank you. It will take time... but your interest is appreciated.

Nice inventory you have there, by the way

Thank you Gary, I'm particularly proud of my universe (Mk I version) I very nearly didn't have one but It's a source of constant joy and amazement

 

[spearbearer]

Well, given that you have it, you must have done something to deserve it! 

[plyscope]

Hi Gary

Wishing you all the best with your project. Ten years ago I built a wooden tube 6" f15 with a D&G lens. You can read my initial thoughts here;

http://www.iceinspace.com.au/41-340-0-0-1-0.html

Since then I've made a few other scopes using similar methods. At the time I could not find suitable aluminium tubing locally here in West Australia. I had experience with building kayaks out of thin plywood and also was inspired by the 6" refractor in Richard Berrys book;

http://www.willbell.com/tm/tm2.htm

Here is a recent picture of my 6" f15. The mount is a home-made alt/az on a fixed steel pier.

[spearbearer]

Hi Andy -

Thank you for this. That is one beautiful scope you have built! The Takahashi Cassegrain isn't so bad either...  :-)

My original inspiration was also Richard Berry's 6" f15 but like you I have decided to do something different from his initial square cross-section design (even though I kinda like it in a retro sort of way). At this point I'm still thinking of an open tube format, but there is a great deal in your blog post which will be very helpful to me as I proceed. For example, I intend to mount mine on a metal pier (8 inch internal diameter ductile iron - I have it already).

Actually, I have seen your build review on iceinspace before, as part of my general 'scoping' (pun intended) of the project, and I have just re-read it with interest. I was particularly pleased to see that you have had some good results with deep sky objects, as these are my main interest astronomically. The reason I chose to build what is usually regarded as a planetary scope was that I like making things (making and observing being two distinct pleasures), but didn't see the point in replicating something of a spec that's easily available commercially (and probably for less money than the build would cost). However, to build a Dobsonian that's outside the usual commercial range would have meant spending a lot more on the mirror than I spent on the objective for the refractor. If this goes well, and doesn't take me the rest of my life, then maybe one day a 24 inch Dob...  No beer on ice yet for that one though!

Cheers,

gary

[Dave Lloyd]

Looking forward to following this thread.

[spearbearer]

Thanks for your interest, Dave.

It will be a slow thread, though...

[Chris]

Can we upgrade SGL to have a "super like" button so I can use it for plyscope's plywood refractor?....it's amazing! 

[spearbearer]

Agree! Thing of beauty...

[plyscope]

Make no mistake a 6" f15 refractor is a large unwieldy thing to manage particularly if you have to mount and dismount each time you use it. If you can make it as light as reasonable and you don't mind the physical handling of it then it can be a very satisfying telescope in use. My current pier is 165mm OD steel and is embedded in concrete block 900mm cubed. The alt az mount is simple and solid but does require very careful balancing.  

This type of telescope is wonderful for deep sky as well as solar system objects. The high contrast and flat coma free field makes the most of the aperture. You can use simple eyepieces without issue. For sure a 6" apo will be even better but not by much. There is a great feeling of nostalgia when using a long old fashioned scope like this. It is not for everyone but there is a lot of fun to be had. 

If you do not have the luxury of a fixed mounting in an observatory then I recommend you make the ota as light and easy to manage as you can. I've managed to keep mine under 30 lbs including finder, diagonal, tube rings and 24" dovetail plate. Even so, it is an effort to lift above shoulder height to lock it into the 16" saddle. A Berry mount has the advantage of being simpler to mount and dismount. The scope is stored in a large box in the shed when not in use. I have to carry it about 15 metres from the shed to the pier each way.

[spearbearer]

Andy -

I'm under no illusions about the ease and portability of this scope. My aim is to keep it in a 'semi permanent' location at my place in France where I am going to install a pier made of 8 inch inner diameter ductile iron flanged pipe bolted to a block of concrete sunk into the ground. I can't sink the pier as for various reasons I want it to also be removable, just leaving the concrete and studs. I think it will be pretty solid anyway.

I'm pretty used to hauling heavy things around and when I'm in France I tend not to be in a rush, which always helps.

If I go down the open tube route that should keep the weight down.

I'm not sure yet about what kind of mount I might use, and will look closely at a range of options including your design. I realize that the type of mount also has implications for the scope design, of course.

Your description of the scope's qualities is very exciting - can't wait to get going on it. Am particularly pleased by what you say about deep sky objects.

Thanks.

[primordial atom]

hi there,

I built a frac from the same lens cell.

Here is a link to the build

http://www.astronomyshed.co.uk/forum/viewtopic.php?f=35&t=24194&hilit=frac