Building a binocular SCT

[sfarndell]

I'm starting my project to build a binocular SCT using 2x meade 8" classic OTAs.

Not sure if it will work for me, but it has been done before. Primary purpose will be for planets, globulars and other smaller DSO's with higher-power magnification is needed.

A key requirement is that I don't want to modify the OTAs, which may be required to get the extended back focus.

The hardest part will be the system to merge the images. Matsumoto EMS is an easy solution, but at c.$2,500 it's not a cheap solution. That leaves replicating it using a DIY design and 3d printing, or leveraging off other ATM'ers who've already done it. I haven't found a source, so please let me know if you have!

If you've done this, attempted it or seriously considered it I'd love to get your input too!

Tools I have access to include a 3d printer and a lowrider 3 CNC (a 3d printed cnc that I made as a lockdown project)

My progress so far has been acquiring the OTAs and designing the frame to hold and align the tubes, with a few parts cut out on the CNC.

[Satchmo]

You might get a bigger knowledge base on Cloudy Nights ATM forum . I would use a split Amici style mirror system for a 90 degree bend and erect images , but the engineering would still be significant .

Reverse newt binoculars would be far simpler to make and probably give better images due to their optical simplicity but you have tools so it would be an interesting project .

[Rainmaker]

Have a look on Cloudy Nights for Jochen’s posts (username Arsmachina)
He has built a few binoscopes like the ones here…..

[sfarndell]

Thanks Mark and Matt.

I’ve seen Jochen’s posts which is what inspired me to attempt this. I have built a 14” F4.6 Newtonian binoscope which is mind blowing to look through, but it needs some refinement to hold collimation at changing altitudes and make the image merging easier. Works best on deep sky, but is ‘ok’ on planets and is not particularly portable, hence experimenting with this.

There is something to be said for completely finishing one project before starting the next, but that is not how I tend to operate. This isn’t going to be a very quick build - the handbrake is mostly going to be in whether I try design something to merge the images and 3d print it, or save up and spend the $2500 for the Matsumoto EMS.

[Satchmo]

Matsumoto designed the split Amici system , which was probably a precursor to his commercial system . Worth tracking down the original S and T Gleaning s article if you can. It will only add one extra reflection beyond a typical SCT.

You really need to use as little back focus as you can in the design as the SCT's start to go soft if you refocus them too far away from the design backfocus, which would defeat your planetary viewing criteria . I think that would negate Matsumot's commercial system .

[sfarndell]

I've built the housing for the tubes. Here are the fusion diagrams. I've only really modelled parts which will be machined (my lockdown project was a cheap 3d printed cnc), and the different are just to help see the components better.
In reality, the parts were all cut from the same sheet of 12mm marine ply and the tolerances were out by just enough (<0.5mm) that it required some wood filler and a lot of sanding to fix and I'll be painting everything to hide the visual defects more. Functionally, the finger joints make it really rigid.

I'll post pics of the real thing when the paint is dry.

[Satchmo]

Looking good.