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Sterope project - design and build a compact 16" binoscope

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#1 Oberon

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Posted 21 March 2015 - 02:21 AM

Merope was my mono dob designed and built as an engineering pathfinder for Sterope - an F/4.5 16" low compromise compact binocular telescope. The key challenges are much the same, only harder:-

 

1. must disassemble and fit in the boot of an ordinary sedan

 

2. must be fast, easy and fun to set up and use

 

3. must have superb optics

 

4. must be easy to collimate

 

5. must hold collimation well and be easy and intuitive to "merge" when necessary

 

6. must be easy to transport inside and outside (wheels), no lifting required in ordinary use

 

7. must fit through an ordinary doorway (~800mm) without being disassembled

 

8. must have setting circles

 

9. must permit use of 2" eyepieces, up to and including the 17mm TV Ethos

 

Although there are some fine bino-scopes out there, to my knowledge nobody has come close to achieving all these objectives in one package before. Bino-scopes are notorious for being heavy, bulky, complex and frustrating to use. At the same time they offer stunning and unforgettable views of the night sky. So in a fit of madness I decided to take on the challenge and see if I could deliver the goods without the bads.


Edited by Oberon, 21 March 2015 - 02:36 AM.

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#2 abberation

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Posted 21 March 2015 - 02:27 AM

I look forward to seeing your design.



#3 Oberon

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Posted 21 March 2015 - 02:34 AM

So far I've just completed my concept drawings of the UTA.

 

gallery_217007_4999_44377.png

 

This is the top down view of the UTA and primary mirrors.

 

The coppery colored rings are not structural, and arguably ornamental, although they could serve to hold the shroud in place should I use a shroud.

 

The red focusers are, well, imaginary. Not dissimilar to Moonlite's they will be engineered to permit an IPD as low as 50mm.

 

The yellow dots are brass knobs of 2 x FeatherTouch Micro focuser.


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#4 Oberon

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Posted 21 March 2015 - 02:57 AM

A couple of views with the top rings removed showing how it works...

 

gallery_217007_4999_8738.png

 

Main UTA structure.

The violet section can be thought of as a fixed frame joined to the LTA by a six pole kinematic truss structure, although not the classic truss as that would vignette the mirrors. This is the core structure against which everything works. More on that later.

Paracorrs
Two Paracorrs will be permanently fitted immediately after the Tertiary.
 

Secondary Support Structures x 2

The two black circles forming the secondary support spider are two short 170mm sections of 350mm (14") x 2.5mm carbon fiber tube from Dragon Plate. They are nestled within and supported by curved sections of ply (blue and brown) fitted inside and outside the tubes. The idea is to make the spider as stiff as it is reasonably possible to make a curved spider. The rings goes behind the two 125mm secondary mirrors to act as (an incomplete) light baffle, and to keep the UTA profile as low and compact as possible. They also protect the secondary mirror from damage when disassembled.

Each secondary support structure slides up and down up to 30mm to bring the Paracorrs into focus. Change of focus is achieved with a FeatherTouch Micro attached to the blue arc inside the CF tube pushing against a teflon rod, which in turn presses against the UTA without restricting rotation.

 

Each secondary support structure may be rotated by >5 degrees to provide an IPD range greater than 50-75mm.

Both rotation and focus utilise the linear bearings on a 10mm rod. They are not attached, the structure simply rests on the bearings which are free to slide and rotate.

 

Not shown is the mechanism that holds the two structures together against the bearings.


Edited by Oberon, 21 March 2015 - 03:07 AM.

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#5 Oberon

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Posted 21 March 2015 - 03:00 AM

Another view...

gallery_217007_4999_184155.png

 

Note the top ring folds down to permit Sterope to fit through an ordinary doorway, much like Merope does now.


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#6 m. allan noah

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Posted 21 March 2015 - 07:47 AM

I am curious about the need to move the paracorrs. Teleview's specs indicate around 55mm distance from the paracorr's flange face to the focal plane. Since you have focusers at the eyepiece, and an independent IPD adjustment, it would seem that paracorr position could be fixed.

 

allan



#7 Oberon

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Posted 21 March 2015 - 07:50 AM

Fixed for me, yes. But other observers will have a slightly different focus, and then there is the effects of seasonal temperature changes on tube expansion. I imagine 10mm would easily suffice, but its just as easy to do 30mm.



#8 Oberon

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Posted 21 March 2015 - 07:52 AM

On the other hand please correct me if I am wrong; possibly the focus correction for other observers is better taken out after the Paracorr. I forget who told me or why I understand that I need to adjust the Paracorr itself for different observers.



#9 Oberon

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Posted 21 March 2015 - 08:41 AM

I think you're right. The only reason given in the SIPS instructions to adjust the Paracorr focus is this...

 

"If the primary mirror moves up or down in its cell due to collimation adjustments that are made over time, the SIPS position should be adjusted periodically to maintain the proper distance between the Paracorr lens group and the primary mirror."

 

Thank you for questioning this. Should save a few hundred dollars and make the UTA even more compact. I can easily make those sorts of focus adjustments with my trusses.


Edited by Oberon, 21 March 2015 - 08:42 AM.


#10 abberation

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Posted 21 March 2015 - 11:03 AM

How do you plan to coordinate primary mirror movement with the secondary?

 

That seems like a pretty big design risk.

 

I would be very tempted to fix everything except the tertiaries and make the mechanics like two halves of an old style linear binocular microscope head (not the pivot type).

 

I don't know anything about paracors but it might be convenient if they could be mounted horizontal between the secondary and tertiary.  That might reduce your minimum IPD.

 

So far I like it, you've got a knack for giving a design some nice curves without pasting them on.  My designs are often lacking in grace.



#11 Oberon

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Posted 21 March 2015 - 04:19 PM

The primaries will literally hang off the UTA on 3 adjustable rods (ie tubes), with another 3 short horizontal tubes for axial adjustment and support. It's a bit hard to explain, but when I've drawn it up it will all make sense.

 

I'm thinking that even the secondaries need some initial adjustment to ensure they align with each other. Ditto the tertiaries. However I'm hoping those adjustments can be very minimal and done as a once off so that all regular collimation is the primaries only.

 

The Paracorr needs to be much too close the the eyepiece to slip a tertiary in between. This means enlarging the secondary, bummer, as otherwise 100mm would have been sufficient. It also means machining off the lip of the Paracorr.



#12 macdonjh

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Posted 21 March 2015 - 04:42 PM

Oberon,

 

Some of us are still reeling from Merope.  Sterope may kill those of us with weaker constitutions.


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#13 abberation

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Posted 21 March 2015 - 06:27 PM

I think I see the pins and concentric arcs that the UTAs will rotate on, I'm still a bit concerned, I'm sure I don't see the full picture.

 

That's too bad about the paracor, I thought they could be used with a diagonal which would pretty much match your setup.



#14 Alex Parker

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Posted 22 March 2015 - 09:05 AM

You are a madman. I am really looking forward to following this!


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#15 starcanoe

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Posted 22 March 2015 - 09:33 AM

I like that part of the design requirement is that it must be "fun to set up" :)

 

One day perhaps we can have scope that are fun to just own :)



#16 Oberon

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Posted 01 April 2015 - 10:28 PM

Development of Sterope's UTA was held up while I took a deeper look at secondary support from a diffraction perspective using Maskulator to simulate diffraction from different support structure designs. If you haven't already been following it see this thread here. It turns out that my proposed 2 x curved vanes weren't far from being the worst design possible, so I've ditched the idea of using a CF tube for secondary support. Instead I'll now fabricate something that presents itself to the sky like this...

gallery_217007_4999_46494.png

 

And here is the diffraction results for this design from Maskulator. For comparison with other designs refer to the thread.

 

gallery_217007_4999_2279.png


Edited by Oberon, 01 April 2015 - 10:33 PM.


#17 Oberon

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Posted 23 May 2015 - 11:10 AM

Or this...

gallery_217007_4999_77611.png

Note unusual use of Moonlite type focuser; the eyepiece tube is clamped to the purple ring, the body is fixed to the green plate, and the green plate supports the eyepiece via an over center bicycle seat clamp or similar (not shown on 3D dwg). This arrangement permits an IPD as low as 50mm for smaller eyepieces, and is limited only by the eyepiece itself for larger than 52mm.


 

gallery_217007_4999_71254.png

 

Lots of detail to be added yet (like mirrors), these are still concept but much closer to cutting.

All truss tubes attach to the yellow section. The purple rings rotate for IPD adjustment, and detach for portability, wheeling through doorways etc.


Edited by Oberon, 23 May 2015 - 11:26 AM.


#18 macdonjh

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Posted 23 May 2015 - 06:37 PM

I think I see the pins and concentric arcs that the UTAs will rotate on, I'm still a bit concerned, I'm sure I don't see the full picture.

 

That's too bad about the paracor, I thought they could be used with a diagonal which would pretty much match your setup.

 

What about Starlight Instruments' SIPS?  Expensive (especially for a binoscope), but may allow the use of a Paracorr for this design.



#19 Oberon

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Posted 24 May 2015 - 12:37 AM

Any standard 2" focuser is too big for a binoscope, aka won't allow a narrow enough IPD. Therefore a SIPS is no good. However my plan is to fit the Paracorr into the rings with a fixed focus (the trusses remain adjustable) and use a focuser mechanism to adjust the eyepiece height above the Paracorr. My eyepieces and Paracorr won't sit in eyepiece rings as normal, but will be clamped.



#20 Oberon

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Posted 10 June 2015 - 09:48 PM

Another design change...

Anyone designing a binoscope larger than say 12" x 2 is likely to start hitting the "ease of use" constraint. Its much nicer to keep one's feet planted on the ground for most practical observing positions, and preferable to avoid use of steps or ladders. This is more difficult to achieve with binoscopes because the eyepieces point vertical when the telescope is pointed at zenith. My own requirements indicated a maximum eyepiece height of 1500mm or 5' which no matter how close to the ground I placed my 16" F4.5 mirrors proved impossible to achieve with a 17mm Ethos and Paracorr.
 

Until now.
 

Lightbulb moment with a big "Duh! Why didn't I think of that before!"
 

Tilt the secondary another, say, 15 degrees and the tertiary to suit. As illustrated. Instant reduction of 200mm (8") height.

gallery_217007_4999_98794.png


Edited by Oberon, 10 June 2015 - 09:56 PM.


#21 Oberon

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Posted 10 June 2015 - 09:50 PM

Tilting the secondary away from 45 degrees slightly increases the obstruction, but in my case this is more than compensated by a reduction in obstruction size for the curved stalk.

gallery_217007_4999_24474.png



#22 Oberon

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Posted 10 June 2015 - 10:06 PM

And Maskulator seems happy enough...

gallery_217007_4999_1441532.png

 

gallery_217007_4999_506682.png

 

gallery_217007_4999_14527.jpg



#23 ckh

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Posted 11 June 2015 - 01:37 PM

Jonathan,

 

Why not use wire spiders? They can be as thin as 0.004 inches, supported by the purple rings. 

 

I assume the eyepieces are far enough from the apertures to avoid obstruction by the observer's head.

 

In post #21, the eyepiece clamping mechanism looks different than before. Can you explain how it works? Do two-inch eyepieces work now since they can be touching?

 

The eyepieces can swing independently, but in practice I doubt it's a problem. The purple rings must be square with and confined along the optical axis, so they cannot tip or fall out.

 

Carl



#24 Oberon

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Posted 11 June 2015 - 04:44 PM

Wire spiders still create noticeable spikes on brighter objects, just not as noticeable as solid vanes. The brain will still object and flicker between eyes.

 

Yes, no obstruction, and enough clearance to fit a tube extension if required.

 

I'll post more detail on eyepiece clamping mechanism when I've drawn it with more detail. 

 

Two inch eyepieces have always worked. The trouble is that when I draw the UTA at minimum IPD (50mm) where everything is square then larger eyepieces such as the TV Ethos 17 overlap, people notice and think I've drawn it wrong. So sometimes (if I remember) I rotate the rings out to create IPD separation to keep everyone happy. Other times I don't.

 

The eyepieces don't swing independently of the purple rings, they only move vertically to focus.



#25 mark cowan

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Posted 11 June 2015 - 05:52 PM

Does anyone have 50mm IPD though? :question:




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