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Sterope project - design and build a compact 16" binoscope

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#26 abberation

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Posted 11 June 2015 - 06:04 PM

Come on, pinheads need telescopes too.


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#27 Oberon

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Posted 11 June 2015 - 06:14 PM

Small children?

My wife has an IPD of 55mm. I don't know what the actual lower limit is, so I've chosen 50mm as a practical limit.

My goal is to build a physical structure that permits a theoretical 50mm IPD, so that the available IPD to any actual user is only eyepiece constrained. In practice I will need some form of "bump stop" to prevent the permanently fixed 51.4mm (2") Paracorr's from colliding, so will probably end up with a minimum IPD of, say, 54mm, just enough for my wife to observe. But it will be very tight, so I'm working to 50mm as a nice easy round number for design purposes.



#28 ckh

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Posted 11 June 2015 - 06:32 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.

 

I get that now. You need to match the views. Spikes would have mirror images which can only be parallel for single IPD. Your unusual diagonal supports help by minimizing spikes.  

 

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.

 

Reading your posts, the problem I was referring to is that some focusers could not be close enough to one another to bring the eyepieces close enough. but you've solved that potential problem in post #19 and in the illustrations that follow.

 

The worst case for IPD is about 55mm which is about 2.17". That leaves just 0.085" for any sort of protrusion on the eyepieces beyond the 1" radius.

 

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

 

I meant that the purple rings rotate independently. They are not constrained to move in equal arcs. As I said, I don't think it's a practical problem.


Edited by ckh, 11 June 2015 - 06:35 PM.


#29 Oberon

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Posted 11 June 2015 - 07:09 PM

 

I meant that the purple rings rotate independently. They are not constrained to move in equal arcs. As I said, I don't think it's a practical problem.

OK I get you now. I haven't drawn a constraint mechanism, and probably won't need one, but do have a simple constraint in mind that can easily be added later if necessary.



#30 Fivemileshigh

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Posted 30 April 2016 - 06:18 AM

Hey, awesome project! I have a couple of questions if I may:

 

1. Have you calculated the length of the optical path from the secondary to the focal plane? (I have some thoughts about that) and,

2. How much do you figure the mirror box is going to weigh?

 

thanks!

 

PS, I just thought, an IPD of 50mm is going to prohibit the use of 2" EP's. I think the lower practical limit is closer to 58 or so. The barrel alone is 50.8mm, that only allows 4mm wall thickness for a focuser, EP clamp, etc....



#31 Oberon

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Posted 30 April 2016 - 07:14 AM

An IPD of 50mm won't work for 2" eyepieces, but it will work for 1.25" eyepieces. Nevertheless I still want 2" eyepieces and everything I do revolves around the assumption I'll be using a pair of 17mm Ethos for wide-field views, which will work for my IPD. Observers with narrower IPDs just won't be able to use my Ethos 17mm, they may have to be content with a Delos.

You don't need 4mm wall thickness for a focuser or clamp. You don't need anything, you can get away with 0mm as my drawings illustrate. You just have to think different.

Assuming the angles in my drawing I have about 540mm from my secondary to the focal plane. If I stuck with right angles that would reduce to 485mm, which would be better. I may adjust to somewhere in between as I play around with the options. What were you thinking?

I won't have a mirror box. The way I see it mirror boxes are back-to-front logic that frustrate good engineering. My mirror cells will each hang from the UTA and be fully adjustable, making collimation and alignment a snack. btw I'm planning to make my cells from modified disc ploughs.

A binocular is fundamentally different to a telescope because everything is defined by an inflexibility of the observer's eyes. To me it makes sense to work out the optical paths backwards from there - basically you do what it takes to create parallel beams from the eyepieces and then align the primaries to that - the result being that it is the primaries (and only the primaries) that need adjusting, but not with respect to each other. Therefore it doesn't make sense to me to plonk them in a box that ties them together, they should be independent.

I won't be using a Stewart Platform like I did with Merope (see my signature link), but the thinking behind Sterope's design is the same. Its much simpler and better engineering to utilise the tube itself to define the relationship between optical components rather than fitting a bunch of secondary mechanisms working against the tube (using the tube as the reference). Its hard to explain...one day I shall draw it!!


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#32 BradleyB

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Posted 30 April 2016 - 09:51 PM

An IPD of 54mm covers just about all adults, but I'm in the 99th percentile at 51 to 52mm. It's very hard for me to find any binocular appliance that will fit. I found the one model of binoculars that fit, the Leupold Yosemite. I've never looked through a binocular telescope successfully. The Denkmeier binoviewers work though, they may be the only ones.

 

Just call me pinhead,

Brad



#33 Fivemileshigh

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Posted 01 May 2016 - 02:01 AM

 

Assuming the angles in my drawing I have about 540mm from my secondary to the focal plane. If I stuck with right angles that would reduce to 485mm, which would be better. I may adjust to somewhere in between as I play around with the options. What were you thinking?

I won't have a mirror box. The way I see it mirror boxes are back-to-front logic that frustrate good engineering. My mirror cells will each hang from the UTA and be fully adjustable, making collimation and alignment a snack.

 

I was wondering about what the final obstruction ratio would end up being.

 

About the mirror box, are you basically building a giant binocular, where each half is held together rigidly and they pivot about a common axis for IPD?



#34 Oberon

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Posted 01 May 2016 - 02:49 AM

No, not that either. There is a 3rd hitherto undrawn and so unpublished way.  :grin: 

 

Sterope will be radical and new; it builds on some things we did with Merope but pushes into new territory also. I'd like to think that when it is finished it will appear a perfectly simple and elegant way to build a big binoscope, and portable at that, but time will tell. I have to draw it first. Then I have to build it.

 

I could build a Dave style 16" binoscope easily enough, but it would prove so heavy and inconvenient I would hardly use it. Note he has a special trailer for it, and I believe he has now sold it.



#35 Fivemileshigh

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Posted 01 May 2016 - 05:49 AM

Re: the Dave bino, I agree, accurately moving large sub-assemblies will likely increase weight significantly. I need to be able to lift the heaviest part by hand. Given my level of knowledge and abilities I think the safest route is moving the EP's. Can't wait to see your solution though!

 

I'll have to draw a sketch to illustrate how I think a 66mm working distance might be enough. I'll have to double check my numbers first.

 

There is also the option of a Baader RCC corrector, 90+mm working distance. Check it out:

 

http://www.teleskop-...mm-Abstand.html


Edited by Fivemileshigh, 01 May 2016 - 05:59 AM.


#36 Oberon

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Posted 01 May 2016 - 06:08 AM

Thats a good idea. Its cheaper too...which may be a worry. And I already have one Paracorr. But if it fundamentally changes my design for the better its very much worth a look. Thank you, I'll give it some thought.



#37 Oberon

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Posted 01 May 2016 - 06:14 AM

And it has a removable ring! That means I don't have to machine off a flange. This is looking good!



#38 Oberon

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Posted 01 May 2016 - 06:35 AM

Well...OK no need to remove flange anyway if its between secondary and tertiary. Also with the tighter angles I'm using the path has increased, its minimum 90mm to the tertiary from focal point, and that again to the CC. Bummer.

 

Still...reopens the option of aligning the eyepieces as you were planning.



#39 macdonjh

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Posted 01 May 2016 - 06:55 AM

No, not that either. There is a 3rd hitherto undrawn and so unpublished way.  :grin:

 

Sterope will be radical and new; it builds on some things we did with Merope but pushes into new territory also. I'd like to think that when it is finished it will appear a perfectly simple and elegant way to build a big binoscope, and portable at that, but time will tell. I have to draw it first. Then I have to build it.

 

I could build a Dave style 16" binoscope easily enough, but it would prove so heavy and inconvenient I would hardly use it. Note he has a special trailer for it, and I believe he has now sold it.

Jonathan, cool link, thanks.  Dave's binoscope looks similar in execution to the JMI reverse binos.  I always thought they were interesting but completely impractical for me as I wouldn't be able to transport them.  That design cries out for a large observatory so the scope can stay put.



#40 Fivemileshigh

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Posted 01 May 2016 - 07:30 AM

Well...OK no need to remove flange anyway if its between secondary and tertiary. Also with the tighter angles I'm using the path has increased, its minimum 90mm to the tertiary from focal point, and that again to the CC. Bummer.

 

Still...reopens the option of aligning the eyepieces as you were planning.

 

If you place it in between the secondary and tertiary, you've got a minimum of 73mm from the edge of the 460mm front aperture to the tertiary (i.e. the length of the RCC), then the tertiary with a 50.8mm minimum optical path length, and then 40.7mm to reach the field stop. (50.8+40.7=91.5mm working distance of the RCC). Total optical path secondary to focal plane 230+73+91.5=394.5mm. A bit better than 485.

 

Might just work.



#41 Oberon

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Posted 01 May 2016 - 08:23 AM

I would still need the 120mm secondaries. What I would lose is the eyepiece height of 1500mm. What I would gain is being able to rotate the eyepieces to a more comfortable height anyway, making the 1500mm dimension moot. That would make the bino-scope much wider and bulkier, and increase alignment difficulties.


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#42 Fivemileshigh

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Posted 04 May 2016 - 05:48 AM

I would still need the 120mm secondaries. What I would lose is the eyepiece height of 1500mm. What I would gain is being able to rotate the eyepieces to a more comfortable height anyway, making the 1500mm dimension moot. That would make the bino-scope much wider and bulkier, and increase alignment difficulties.

 

I've been trying to figure this out. I can see how the scope will be wider, obviously, but I don't see how that will make it more difficult to align? the LOA would be one rigid piece, so would the UOA, as it won't have the Dave-style rotating rings for IPD adjustment. The secondaries would have to have an adjustment for aiming and for position (i.e. to place the optical center of the secondary in line with the optical axis of the primary). This adjustment shouldn't be too hard to do with a rigid UOA. It can be achieved by adjusting the spider tensioning nuts in pairs for example.

 

What am I missing?



#43 Oberon

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Posted 04 May 2016 - 07:53 AM

I suppose the key difference is that whereas an IPD adjustment done with a small rotation of the UTA only creates a very small angular rotation, and thus little risk of mechanical eccentricity introducing demerging, a rotation done at the eyepiece in altitude for user comfort involves up to say a 60 degree rotation, with a corresponding high risk of an eccentricity introducing a misalignment or demerging. 

 

Maybe I'm only imagining it to be a problem when in practice it isn't; I guess the bigger issue is that I haven't worked out out how to solve it elegantly were it to prove a problem. Otoh I'm perfectly familiar with the issues associated with rotating an instrument on the AAT - perhaps the finest mechanically engineered telescope in the world before the HST - meaning that it is incredibly difficult to ensure that the optical axis and the mechanical axis are the same thing. Basically it's an impossible task, and there is nothing like a rotation of a angular mirror at high magnification to expose it. Think about it...you've aligned everything and got it all merged...all looks great...but you wouldn't notice that the FOV are in fact say 2min of arc misaligned so long as the stars are aligned. Beautiful.

 

Until you rotate the tertiary. 

 

Irrespective, I won't be making the LOA in one piece as that just cramps my style and begs for problems. There is a reason why most binoscope makers end up putting motorized collimation screws under their mirrors, and the reason is that their binoscopes are hard to collimate. See JMI. Sure they think they've solved the problem but in fact they've added complexity and compromised rigidity. Its poor engineering masquerading as a solution.

 

However I agree with the UTA being one solid piece. That makes sense.



#44 Oberon

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Posted 13 June 2016 - 02:48 AM

Sterope construction officially begins today.
 

Under the clamps are two sheets of thin 3mm ply sandwiching a 25mm sheet of end grain balsa destined for the UTA and a layer of CF. Light and stiff.

I should really be doing this by vacuum bagging, but couldn't wait for my bags and seals to arrive. Next time.

gallery_217007_4999_58910.jpg


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#45 brucesdad13

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Posted 13 June 2016 - 02:34 PM

Congratulations! :band:  :gotpopcorn: :like:  I've not yet glued sheets of wood together. Did you say with Merope that you used polyurethane glue? Will you get a CNC mill or still making interesting tools for all of the angles?

 

 

Sterope construction officially begins today.
 



#46 Oberon

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Posted 15 June 2016 - 08:24 PM

Hi BD with Merope I used PVA glue (external grade) when gluing timber to timber (i.e. when laminating sheets of plywood #7), and I used polyurethane when laminating any other material to the plywood, including the CF sheet #94, laminex altitude bearings #68, lamipanel azimuth bearings and base #7, the acrylic setting circles #36 and the glossy black ACP sheet #61.

 

I'm afraid a CNC mill is dream territory at present. :)  



#47 brucesdad13

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Posted 15 June 2016 - 10:05 PM

Jonathan, seriously look at this unit I got in December. I bought the 1000mm x 1000mm package. It is probably less than what you've spent on a few eye pieces for Sterope. https://www.inventab...ologies/x-carve (full disclosure I have no connections with Inventables just a happy customer).

 

Hi BD with Merope I used PVA glue (external grade) when gluing timber to timber (i.e. when laminating sheets of plywood #7), and I used polyurethane when laminating any other material to the plywood, including the CF sheet #94, laminex altitude bearings #68, lamipanel azimuth bearings and base #7, the acrylic setting circles #36 and the glossy black ACP sheet #61.

 

I'm afraid a CNC mill is dream territory at present. :)  



#48 brucesdad13

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Posted 15 June 2016 - 10:08 PM

Also, I can't seem to find double flanged track wheels or roller bearings or whatever it is that you used to attach bicycle wheels to Merope. Ideas? Everything I find costs $30 or more ea.



#49 Oberon

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Posted 15 June 2016 - 10:17 PM

You're right. I'm sold.

Which software should I buy?


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#50 Oberon

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Posted 15 June 2016 - 10:21 PM

Also, I can't seem to find double flanged track wheels or roller bearings or whatever it is that you used to attach bicycle wheels to Merope. Ideas? Everything I find costs $30 or more ea.

 

Pulleys. Here.


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