Help me make a cheaper Swarovski BTX (1 Viewer)

Hello birdforum! I haven't posted here in a long time, and have lived in other areas far away from where I once often used spotting scopes, but it is good to see that some of the helpful people that I remember are still here (Henry, FrankD, many others!).

So I want a Swarovski BTX, preferably one with zoom. Ha! Even at $5k, it still doesn't have zoom (although I am aware of their optional magnification extenders). So coming back down to earth...

My question is then this: Has anyone here been successful in making a 45-degree angled binoviewed spotting scope out of telescope parts? My understanding is that no one has succeeded in putting a binoviewer on angled spotting scope refractor bodies, even including creative use of telescope parts, except for Swarovski. I also know that DRodrigez has made some amazing creations, but none that are angled so far as I know, and anyway his creations (that I've seen) are very large and perhaps too delicate for me to rapidly and repeatedly take out of the back of my Subaru. I am aware of that Celelstron C5 "spotting scope," but with a binoviewer on it, it's over 50x *to start*, and I'm unsure of its visual quality?

Perhaps something like this would work:

- 100mm-ish refractor body, a short one probably
- 45 degree image erector (amici? Needs to be high-quality from what I've read)
- binoviewer, preferably one with powers (which is like zoom), like a Denkmeyer Binotron with Powerswitch
- eye pieces giving me reasonable spotting-scope-strength powers

I have read here, and especially in Cloudy Nights, of many issues with trying to make binoviewers work, especially one like the Denk with power switching. Issues that I don't even understand the math of what went wrong. Backfocus is commonly mentioned. CA is often mentioned. F/ apertures too. Machining the the tubes shorter has been mentioned, and I have no idea how to even approach that.

I have posted this question over at Cloudy Nights a few months ago, and had to leave it in limbo for a while. But now I've got time and energy to tackle this again.

I would truly love to hear of ANY specifics on ANY system that ANYONE has made to work. Even without powers/zoom, if that's what you got to work.

I realize that some may suggest various binoculars, but I've not seen a reasonable pair (for my use case) that has both 45 degree angle and center focus. And forget about zoom. If I cannot have have 45 degrees, then I would be forced to buy two binoculars (myself and wife), and the two tripods for them, and to take both rigs in and out of back of Subaru a lot. Which, since I am running into so many obstacles, perhaps I should consider as a real option.

Thanks sincerely.

For Astro scopes (1.25” eyepieces), I’ve been round this thought recently. 45degree erecting prisms exist, many reasonable binoviewers exist, for zoom the only option is the baader mk4 clickzoom eyepiece. The trouble is backfocus, so unless you use a magnifying Barlow lens (restrict yourself to high power) you’ll need to cut the tube down to reach focus.
The catadioptric approach won’t need the Barlow, but have very long native focal lengths… so back in high mag land again. I have a suitable 80mm scope, but prefer not to risk destroying it.
I’ve put the idea on hold as the cost is spiralling. If you want a chopped scope you could give APM in Germany a call, I got a small finder scope custom shortened by them once, do it professionally!

Good luck

PEter

wllmspd said:

For Astro scopes (1.25” eyepieces), I’ve been round this thought recently. 45degree erecting prisms exist, many reasonable binoviewers exist, for zoom the only option is the baader mk4 clickzoom eyepiece. The trouble is backfocus, so unless you use a magnifying Barlow lens (restrict yourself to high power) you’ll need to cut the tube down to reach focus.
The catadioptric approach won’t need the Barlow, but have very long native focal lengths… so back in high mag land again. I have a suitable 80mm scope, but prefer not to risk destroying it.
I’ve put the idea on hold as the cost is spiralling. If you want a chopped scope you could give APM in Germany a call, I got a small finder scope custom shortened by them once, do it professionally!

Good luck

PEter

Click to expand...

Thank you for your help, Peter. Yes, the minimal 50x-ish magnifications are a big issue. Have you any thoughts on the Denkmeyer Power Switch system? If I were to try to locate a chopped scope, do you think I could eventually succeed with either that or the Baader clickzooms in getting the lowest power to be about 30x-ish?

Is there any telescope maker that makes already shortened scopes?

No reason it shouldn’t. I am just being cheap.. I got lots of toys on the list to get and not enough pennies! I have looked for “imaging refractors” as these need to have enough focus travel for DSLR usage, I have an imaging Newtonian and I need to use an extension tube with eyepieces however 100mm has been mentioned for binoviewers, so even this might not be enough... a saw may be needed still. Aim to over shorten, adding a short extension is a lot less painful than finding it still won’t reach focus. It should then be possible to run with no Barlow, so 20mm focal length eyepieces can deliver their native focal length. Magnification depends on the scope you couple it to.

Good luck, you are entering less charted land!

Peter

After a lot more reading, I think the sane idea is for me to give up. Too much to go wrong that's above my knowledge/desire/time to fix. I do not want to be spending so much money, returning parts, cutting tubes in pursuit of something that may never even work, of which problems I don't even really understand.

I simply refuse to spend $5k on a Swarovski BTX system. I can only hope that a more affordable manufacturer like Vortex may create something like that in the future.

I will leave this reply here in case someone comes along in the future, and can post the details of a working system made with reasonably available parts. Something like 80mm to 100mm, light enough to transport, 45-degree diagonal, (Denkmeyer) power switching, and reasonable spotting-scope-level magnifications.