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Would 2x raci finders make a low power binocular?

Binoculars ATM
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#1 Binofrac

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Posted 27 October 2021 - 04:35 AM

My 10x50 binoculars on a monopod are my most used astronomy gear but of course are a bit of a strain near the zenith. I have tried the various mounting options with a zero gravity chair but like to be more on my feet and mobile. A right angle binocular would be ideal but are not available in the lower powers. A mirror mount would be quite a bulky thing, and the large first surface mirror involved looks quite vulnerable if not used on a table or surface of some sort.

 

Using my 9x50 raci finder the other night made me wonder if two of these could be coupled together to make a reasonable binocular. If the crosshairs were removed and each was held in a couple of finder rings screwed to a mounting of some sort, it would be possible to adjust the IPD and collimation via the ring screws. I'm presuming that finder manufacturing tolerances are tight enough to use two finders from the same company.

 

I've searched around to see if this has been covered before but only found binoculars converted to finders, not the other way round.



#2 Bkoh

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Posted 27 October 2021 - 04:51 AM

Using my 9x50 raci finder the other night made me wonder if two of these could be coupled together to make a reasonable binocular. If the crosshairs were removed and each was held in a couple of finder rings screwed to a mounting of some sort, it would be possible to adjust the IPD and collimation via the ring screws. I'm presuming that finder manufacturing tolerances are tight enough to use two finders from the same company.

I've searched around to see if this has been covered before but only found binoculars converted to finders, not the other way round.


https://www.cloudyni...x-50mm-finders/

In the thread above, very high quality finders (Stellarvue) and eyepieces (Televue) were used, but in principle any 2 RACI finders could work.

#3 Binofrac

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Posted 27 October 2021 - 05:16 AM

Thanks Bkoh,

 

It seemed such an obvious idea that I was sure someone must have done it in the past.



#4 Jon Isaacs

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Posted 27 October 2021 - 06:21 AM

Thanks Bkoh,

 

It seemed such an obvious idea that I was sure someone must have done it in the past.

 

The difficulty is building the fixture to hold the finders.  For a single user, the IPD could be fixed so it could be shimmed.

 

I actually purchased two of the Astro-Tech 50mm RACI finders with the idea of building a binocular telescope.  They're only $45 each and have a nice helical focuser.  Optically, they're much sharper than my StellarVue 50mm RACI finder.  I was able to split Porrima (3").. 

 

The problem is the OTAs are 62mm in diameter so your IPD would have to be at least 62mm.  I ended up just using them as RFTs and as a finder for my Dobs. 

 

https://www.cloudyni...45-50mm-f5-rft/

 

They come is a variety of colors, here's the black one.

 

https://www.astronom...ack-finish.html

 

Jon


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#5 PEterW

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Posted 27 October 2021 - 07:15 AM

I’m part way through this…. Currently fixed IPD and “jiggle” to focus/collimate. I’ve got plans for fixing both of these in version 0.2. I added a groove for a laser pointer and a synta dovetail so I could plonk it on an as-gti and have goto. Given the nice centre of gravity it is quite easy to use handheld. I can change 1.25@ eyepieces, but given the fast lenses you aren’t getting a flat field! Its an obvious gap in the market as looking at the zenith is a pain in the neck and no one makes smaller aperture angled binoculars… not that the market would be especially big.

Peter
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#6 Jon Isaacs

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Posted 27 October 2021 - 07:19 AM

I’m part way through this…. Currently fixed IPD and “jiggle” to focus/collimate. I’ve got plans for fixing both of these in version 0.2. I added a groove for a laser pointer and a synta dovetail so I could plonk it on an as-gti and have goto. Given the nice centre of gravity it is quite easy to use handheld. I can change 1.25@ eyepieces, but given the fast lenses you aren’t getting a flat field! Its an obvious gap in the market as looking at the zenith is a pain in the neck and no one makes smaller aperture angled binoculars… not that the market would be especially big.

Peter

 

Peter:

 

What finders are you using, what eyepieces?  

 

jon



#7 TOMDEY

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Posted 27 October 2021 - 07:30 AM

Yeah, that will work... the tough part is the co-alignment and getting them close together according to your personal Interpupillary Distance (IPD).

 

I did that with my Night Vision to build true binoscopic at 1x and 3x, using Howie Glatter's PST BinoPlatform© That comprises UDLR alignment adjustment built right in and the excellent IPD adjustment using that big knob on the left.    Tom 

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  • 96  85 Glatter Bino Platform.jpg
  • 95 85 Glatter Bino Platform.jpg

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#8 TOMDEY

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Posted 27 October 2021 - 07:31 AM

nother picture    Tom

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  • 94 ITT Night Vision 1x and 3x binos Tom.jpg

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#9 Rutilus

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Posted 27 October 2021 - 08:13 AM

I've just held to together, you will have to remove one of the adjusting screws from the finder bracket.

with it in place the IPD is around 75 - 80mm. With it removed I got around 63 -65mm.

 

For astronomical use I built this unit (works with two 50mm lenses from standard Synta made

finder scopes. I use magnifications from 4x up to 20x, and by using a two simple focal reducers

(cost around £5-£10) built into the two inch eyepiece holders I get a maximum fov of 16 degrees.  

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#10 Rutilus

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Posted 27 October 2021 - 08:14 AM

Version using two standard Synta finder scope lenses.

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#11 TOMDEY

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Posted 27 October 2021 - 09:21 AM

Oh --- just remembered --- I invented this binoscopic "Penta Mirror" dingus about forty years ago. It works great, and you can use any regular binos with it. The image is correct handedness (parity) and right-side-up. The business itself is long ago defunct... I just grew weary of working...   Tom

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  • 98 1982 CATALOG Dey Optics RACI Penta Mirror.jpg

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#12 TOMDEY

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Posted 27 October 2021 - 09:22 AM

pictures of actual embodiment of Tom's Penta Mirror. Others have also successfully done this.    Tom

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  • 97 Toms Bino Penta-Mirror Diverter 2 74 98.jpg

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#13 PEterW

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Posted 27 October 2021 - 10:56 AM

I am using cheap generic 50mm 13m focal
Length funders, had a straight thru and an amici model… same front end when you cut the tubes down. I bought some amici prisms as the cheap ones are too small. I am using 24mm UFF and other shorter length ones I have for a binoscope. Similar to Tom, my IPD adjustment will use some ground steel rods riding in tight fitting 3D print guides and a threaded rod and spring to keep stuff from moving.

Peter
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#14 ihf

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Posted 27 October 2021 - 11:39 AM

Agena may soon have a new prism for these kind of setup "Kasai Trading 1.25" Erecting Zenith Prism (EZP) Diagonal". It is a bit expensive though at USD 265 per prism. It would also require a platform similar (or better) to the one mentioned by Tom. There is a big and expensive one made by AOK. I think I saw one or two less expensive ones by 2047. Maybe Range88 could offer to forward those?

 

kt-bino-diagonal.jpg


Edited by ihf, 27 October 2021 - 11:58 AM.

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#15 ihf

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Posted 27 October 2021 - 11:58 AM

I got an SVBONY SV410 9-27x56ED recently hoping I could replace the eyepiece for 11x56 using the 18mm UFF. The exterior diameter is 66mm (about 5mm thick metal walls, could be ground down a bit to reduce IPD for my 62mm and stick together). The nice thing is it has a color free lens as promised. There are a few problems: it has a focal length of f=189mm so f/3.38 and as expected a murderously curved field even with UFF lenses (I think the 4 front elements are for focus not flattening). I think the field is not fully square but it was hard to tell. As one could have suspected in the pictures the prism is too small for 18mm UFF field stop (adequate for the zoom) and there is not enough space to safely place it. But the 10mm UFF can be shimmed to some degree[1] and I think an improvment over the zoom for an 18x56. But still not flat to the edge. While I had interests for an angled 11x56 I don't have the same interest in an angled 18x56 as I am perfectly happy with the Canon 18x50. So at this point need to spend some time to decide if I want to permanently convert it to lightweight/tiny 18x56 spotting scope (just under 500g with the much smaller 10mm eyepiece). Unfortunately the foot doesn't rotate to the side, so it isn't an ideal small spotter. It is fairly steady in the hand though, so maybe there are other lightweight ways to stabilize (like a neck band).

 

Anyhow, just showing how experiments in gluing 2 small scopes together can easily get sidetracked.

 

[1] I am still looking for the right step up ring, but I think I will have to permanently glue the 10mm flat to the top plate which if I don't want to spend ridiculous money.


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#16 pretyro

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Posted 31 October 2021 - 12:10 AM

Oh --- just remembered --- I invented this binoscopic "Penta Mirror" dingus about forty years ago. It works great, and you can use any regular binos with it. The image is correct handedness (parity) and right-side-up. The business itself is long ago defunct... I just grew weary of working...   Tom

   For your "Penta Mirror", how flat does it need to be for various binocular powers?   I am assuming a binocular of greater magnification would need a flatter mirror.     I am considering putting something like this together.   Some of the really flat first surface mirrors that would be large enough seem to cost North of $1,000. 


Edited by pretyro, 31 October 2021 - 01:34 PM.



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