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Bino 77mm....


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A few months ago I posted something about restoring a 77mm refractor
During cleanup in one of our 'forgotten corners', believe it or not, I discovered (covered completely with dust) exactly the same refractor as the restored one.

Needles to say these two scopes are candidates to make another binocular...:bino2:


Except for the serial nr, these two are identical


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Bino's...story of my life, and I'd rather call it an addiction...🤭

Busy drawing parts already.
Not far from that refractor I also found a very old C8 fork, it's a first generation I think(very ugly green).
I'm thinking using that fork to support that bino. I'll make a system to keep that bino horizontal all the time while tracking.

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There's not to much work involved this time.
Both the tubes and cell's are in good condition. So that only leaves me the support unit(cradle) and also the focus/IPD unit to build.
My goal(as aways) is our open door mid Sept, so plenty of time. After open door I'll 'release' it in the hand of our youngsters...
I hope they take good care of it...🤨

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This is a first idea
There are in fact two cradles.
The brown is fixed in the mount. The red one is attached to the two scopes.
The upper part of the brown cradle can be removed and locked with bolts. So the bino itself can be removed for easy transport.

As I said before I will mount the complete unit into an old Celestron forkmount.
While tracking the scopes, in fact the eyepieces, needs to stay horizontal. That is why the red cradle will rotate in the brown one. Smooth gliding will be done on Teflon pads.

The Focusing and IPD unit (busy drawing) is completely selfmade. For that I need 4 small diagonals(31mm).

To have an idea how big this is ; the diameter of the brown part is 230mm  --> fits exactly in that Celestron fork.


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Eyepiece end design of a binoviewer is largely dictated by the translation distance between the objective centres and the IPD of the user.  For small binoviewers I have used a pair of monoculars and for units up to 120mm aperture, wide angle binoculars.  90 degree eyepiece angle large models usually require multiple prism arrangements.       🙂 

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I will use the same setup as in my 150mm binocular.
And I'll add a readout apparatus so I can see on a small screen how far apart the eyepieces are. I will also make  a handheld measuring device so the observer can read what his IPD is. Have to think about this, how to make it.

Edited by Chriske
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  • 2 weeks later...

While cannibalizing the two refractors I saw a few baffles in the tubes. Nothing wrong with that of course but the holes in these baffles are way to small. Looking through the hole, were the eyepiece supposed to be, I could not see the spacers of the 77mm Fraunhofer lenses at all. I even needed to shift my head to the very perimeter of the eyepiece barrel to see these spacers.
Seen from the eyepiece location I expect to see these spacers.Could it be that using (to) narrow baffles, these scopes cover up mediocre optics.???🤔

I've seen it before in some very cheap (50€ or so) telescopes sold in warehouses. One time I took apart such a cheap  70mm f/10 scope and found very close to the lens, about 25mm or so, a 50(!) mm diameter baffle. A few moments later I found out that the lens was only '1' lens. And that single lens wasn't even a doublet. It was nothing more the a convex/flat piece of glass...😳. I expect to see nothing more then the Moon or so with that kind of 'scope'. On the box were the scope was sold in, there were lots of promising markings, one of them was that the largest magnification was 600x(!!) Furthermore you could see the portholes of a ship that was miles away.

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I strongly suspect that the reduction in effective aperture is to further control aberrations.  I have seen many such instances in entry level refractors.  Interesting that at least the box recommends use for terrestrial and bright astronomical use, areas where the reduction in image brightness would be least noticeable.      🙂 

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There are, however, plenty of small inexpensive entry level refractors that have good optics even though the supplied mounts and accessories are of poor quality.  The generic 60mm F11-ish objectives are usually surprisingly good, the ones I used for my binoscope easily supported 120x and were full aperture.    🙂 

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