New layout for a refractive astronomical binocular
Posted 18 June 2010 - 04:00 PM
Also, it seems to me that two commercial telescopes could be modded in-to this configuration with custom brackets and a little shortening of the tube depending on how much back-focus the focuser provides. Such brackets would be very easy to make with a mill. Mind you with simple brackets it would be hard to collimate the tubes unless the lens cell was collimatable. But heck it might not even be needed if the construction was not extremely imprecise.
With a little added complexity you could make the bracket collimatable for one tube, and with some significant added complexity the IPD could be adjusted.
You have not presented any viable idea for implementing IPD adjustment.
Posted 18 June 2010 - 06:28 PM
For about 1 year that I have designed and planned building such binoculars.
I initially thought about using 2 Borg 50 scopes which have 60mm OD. I am now seliing them on CN classifieds.
But wanting to use better scopes, I have made all the design plans and calculations for such setup as you describe. Several pages of calculations, with specific scopes, diagonals, eyepieces, etc.
The scopes of my choice are Tak Fs-60CB with 80mm OD and TV102 with 120mm OD. No modifications to the scopes are necessary, and they can used separate or in binocular setup.
There are four main issues to deal with:
1. Back focus
My calculations give that 80mm OD implies 53mm of scopes offset, and 120mm OD implies 104mm of scopes offset.
The TakFS-60CB accommodates the 53mm even with a filter wheel.
The TV102 must be paired with a TV102iis for the focus range.
2. Full illumination of eyepieces field
In order to compensate for the additional distance from focus plane, one diagonal needs to be bigger than the other.
I calculated that using a Baader 2” diagonal on one scope and a Baader T-thread diagonal one the other gives approximately 30mm of fully illuminated fields on both scopes (Tak 60).
Baader diagonals have the advantage of being modular and therefore allowing shorter travel distance (we can eliminate nose pieces and eyepiece holders).
3. Diagonal and eyepieces width
If we use two 1.25” diagonals or two T-thread diagonals, one of the scopes will have significantly reduced fully illuminated field of view.
On the other hand we cannot use two 2” diagonals as the typical width is 65 mm, and therefore will exclude many people.
Also 2” diagonals take more focus travel.
So the perfect solution is to use one 2” diagonal and one T-thread diagonal, for three reasons:
a) 2” diagonal is 65mm width and T-thread diagonal is 50mm width. So we have an average of 58mm which is quite fine.
b) Regarding field illumination, having the second diagonal smaller is quite fine as it is closer to focus.
c) Regarding focus travel, the smaller diagonal will be on the critical focus travel scope, so we save there.
For eyepieces I use any eyepieces that have width smaller than 58mm, my target for interpupillary distance. Also I use only eyepieces with field smaller than 30mm in order to get fully illuminated field.
4. Holding the scopes, Adjustment of interpupillary distance, and scope rotation.
I have it designed also but that is another history, this post is long already.
Posted 18 June 2010 - 06:53 PM
We don’t have it anyways in a regular binocular. In order to keep perspective with a 10x binocular, we would have to be 10x closer, meaning that at a distance 10x farther, the scopes need to be separated by 10x our interpupillary distance. As they are not, 3D effect is reduced to near zero, so it does not matter if the scopes are stacked horizontal or vertical.
Posted 18 June 2010 - 07:56 PM
Posted 19 June 2010 - 06:54 AM
There is absolutely nothing new in this design:
Very nice. Thanks for the link.
There seems to be there some optimized models and others not so much.
We can see that several of models in the link use a larger diagonal in one scope to compensate the distance from focus, while others do not, which results in vignetting.
Also some models minimize the distance between the scopes, while others do not. Less distance means less scope offset.
Don't forget to see the link in the middle of the page, in which is shown the importance of one larger diagonal.
The only scope which I guess will sub-perform is the last one in this page: http://www.zellix.de...stbau/binos.htm :-)
Posted 19 June 2010 - 12:41 PM
One aspect of it I am not understanding - the parallelogram linkage. The 3-D rendering shows a monolithic tube, but would not separate tubes be required for the IPD adjustment? And the linkage would need to attach to both ends of the tube.
Posted 22 June 2010 - 11:44 AM
Thrawn, my intention is to acquire a second Jaegers 6" f/10 objective lens, after which I will start construction. It's clear at the moment that I'll have to wait for a while. Maybe next summer. I'm up to my eyeballs in projects non-astro. Sad case.
As far as IPD adjustment, the parallelogram structure was an idea for that. As long as the two eyepiece tube axes can be kept parallel, the images once superimposed should remain superimposed as the IPD is adjusted. The longer of the two tubes post-diagonal will sweep farther than the other for a given angular tweak, changing the IPD. The relative vertical (axial) locations of the two exit pupils will change slightly with the adjustment, but that is easily accommodated as long as the adjustment is not large.
Pedro and Thomas, I'm glad to see that this idea has been developed. It shows that it's viable. I'm even more motivated to make it now that I know that real examples exist. Pedro, thanks for your info. It will certainly help when I get to brass tacks.
Jeff, the linkage is only one possible concept for adjusting IPD. The brute force way would be to have one of the two scopes mounted on a lateral slide, such that different observers would only need to turn a control to move that scope laterally until the IPD is right for them. In the concept I show in my article, the telescopes themselves never need to be adjusted. The main telescope assembly should be designed so that it holds the two objective lenses at your personal IPD in the horizontal direction, as my sketch shows. Given that, the two eyepiece holder tubes extending up from the diagonals will then also be spaced by your IPD. However, if the two tubes can be rotated slightly in angle - by precisely the same angle - around their own telescope axis, so that they lean to one side in tandem, then the IPD will change without the two images becoming mis-aligned. The linkage was there only to maintain equality in rotation angle between the two eyepiece tubes.
In the concept that I showed in my sketches, the rotation occurs via the diagonal tubes that are inserted into the focusers. An alternative would be to make the main-tube end plates, which mount the focusers to the main tube(s), rotateable. Maybe something like a rotating head mechanism would work such as on Bob Royce's Ultimate Newt tube assembly. They could be geared to keep them in angular synch. I'm not capable of such construction myself, so I opted for a simpler idea.
To the folks overseas who have made this type of binocular,
Thanks and Clear Skies,
Posted 22 June 2010 - 02:19 PM
Edit: link now works
A small tug on the bottom link of the mechanism to the left will rotate both star diagonals through an equal angle, moving the eyepieces a bit closer together.
Posted 22 June 2010 - 07:37 PM
In the article, he describes what he learned from his project (apparently the hard way!) about the particular vagaries of the asymmetric layout. He also gives some observation notes, which only make me crave this project even more.
Posted 23 June 2011 - 05:44 AM