Mirror Mounts for big Binoculars

[Art McConnell]

Except for the price of the binoculars and a good mirror, mirror mounts are easy and cheap to build. Since one advantage of binos is the wide field of view, the limited magnification of less expensive mirrors ( I got a one wave for under $100) is not so much of a disadvantage for wide field wiewing.  The ease and speed of sweeping through a dark star-filled sky makes my mirror mount a joy to use.

This is what I did with my BT70 binoscope (everything but the mirror and binos came from my scrap pile):

 

The pedestal is height-adjustable (one pipe in another), and mounted on a lazy susan-type turntable off an old swivel chair, rotates 360 degrees.

I just came in from viewing the moon at 63x, and was pleasantly surprised at the clarity of the image my 1 wave mirror produced.

Edited September 28, 2021 by Art McConnell

[jjohnson3803]

Interesting!  When I was researching mirror mounts for binos, I seem to recall a lot of insistence on 1/4-wave mirrors, which were really cost prohibitive, so I dropped the idea.   I'd be using it with only 15x70s, but tilting my head back can be problematic due to some old injuries so a look-down would really help.

How did you calculate the size of your mirror?

Edited September 28, 2021 by jjohnson3803

[Peter Drew]

I built a mirror mount for a self built 102mm binoscope using two 102mm F5 Startravel refractors.  I used a 260mm x 275mm first surface mirror from an early Xerox photocopier.  The views at 20x were fantastic, I really must rig it up again this Winter.  Large mirrors are available from Vacuum Coatings Ltd on occasion.  You usually need a mirror slightly larger than the width of the binocular and around 1.5 x for the major axis for full coverage.  It is possible to use two smaller mirrors, one for each objective amd mount them on a common base with one of the pair adjustable to merge the images.  The rock steady image is a joy to behold.

[Art McConnell]

5 hours ago, jjohnson3803 said:

Interesting!  When I was researching mirror mounts for binos, I seem to recall a lot of insistence on 1/4-wave mirrors, which were really cost prohibitive, so I dropped the idea.   I'd be using it with only 15x70s, but tilting my head back can be problematic due to some old injuries so a look-down would really help.

How did you calculate the size of your mirror?

I had a large non-first surface mirror on it first, cut a cardboard template to cover all but what was needed. 6x9 was as small as I could go, and still use my laser pointer, which had a slight vertical offset from my optical axis.

I had my 6.3mm plossl in it this morning, and the moon was as clear as I could expect it to be. With a F/L of 400mm, it would have been about 63x. Just fine for deeper wide field viewing.

The mirror was $79 plus shipping, less than $100. I got the mirror here:

https://firstsurfacemirror.com/glass-first-surface-mirror/ 

 

 

 

with

Edited September 28, 2021 by Art McConnell

[Merlin]

I was lucky to obtain a superb ex- military mirror for my homemade mirror-mount. It cost just £3 on a flea market. It’s so good that I bought a second one the following week. The coatings are perfect.

Originally, the mirrors cost over two hundred of pounds each. They were well boxed and could be war surplus, which would make them very pricey on today’s money.