How to build a binocular mirror mount
Take the strain out of binocular astronomy with our guide to building a binocular mirror mount.
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A zip folder containing materials required for this ‘How to’ is available here.
Binoculars are invaluable tools for amateur astronomers, but for effective use they need to be held steady for long periods of time.
This is both tiring and challenging, particularly if the binoculars are heavy.
This month we’re going to build a table-top binocular mount with an adjustable mirror and pivoting base for hands-free observations.
With this, you can simultaneously take notes, make sketches, or even share the view with companions.
Best of all, at all times you look downward into the binoculars at a comfortable angle, so you never have to suffer that cricked neck feeling again.
Finish – Exterior quality gloss paint or varnish, or an oil or wax finish, depending on the wood and the effect required.
Materials – 12mm plywood for mirror base and round base; approximately 2.7m of 32x18mm softwood or hardwood; 205x152mm front-surface mirror.
Sundries – No.8 x 1.25-inch brass woodscrews, three M8 x 60 countersunk bolts with wingnuts and washers, 12-inch vinyl record, felt furniture pads, rubber feet for base.
Tools – Tenon saw, coping saw, drill with bits for screws (8 for pivots, 4.5 for clearance, 2.5 for pilot holes) and a countersink bit, sandpaper, ruler, pencil, screwdriver.
Beware of the ghosts
Our design uses stock-sized timber and requires only minimal woodworking skills.
The type of mirror you need is a first- or front-surface mirror.
This means the reflective surface is on the outside face of the glass, rather than underneath it as in a typical mirror of the type you might have in your bathroom.
The reason why is that front-surface mirrors produce a single clean reflection, whereas the bathroom type produces a second ‘ghost’ image from the outer layer of the glass.
The mirror surface is delicate, so care is needed when handling it; we’d also recommend a cover to protect it and prevent dust building up when not in use.
We sourced our relatively inexpensive mirror from Vacuum Coatings (www.scientificmirrors.co.uk), but there are other companies you could purchase one from.
The quality of the mirror surface is important – ours is fine for binoculars in the 50-70mm range and we have designed the mount to suit binoculars of this size.
Larger (say 80-100mm) binoculars could be accommodated with a scaled up design, but the quality of the mirror and subsequent cost may become the limiting factor – it is worth discussing your requirements with the mirror supplier if in doubt.
All the timber frame parts are made from 32x18mm wood, which is a common size found in DIY stores.
We were lucky to obtain some nice hardwood, but good quality softwood is fine.
The round base and the mirror base are made from an offcut of 12mm plywood, but a similar thickness of MDF would be ok.
The pivots for the mirror and base are M8 bolts with nuts and washers.
A wingnut is used to tighten and loosen the mirror during repositioning.
The special low friction base is just an old vinyl LP record (Holst’s The Planets would be most appropriate) stuck to a plywood disc, with some felt pads under the frame gliding around above it.
Alternatively, you could simply move the frame about on a smooth surface or improvise a tripod mounting.
Use the pivot hole position to determine the centre of gravity or balance point if you take the tripod route.
The mount is delightfully simple to use: just sit it on a suitable table, turn it so it is facing the area of sky you wish to observe, and then rotate the mirror to bring the view into position.
We found it was quite easy to look into the mirror along the top of the binoculars to achieve a close enough aim.
You do get a reversed and upside down view of the sky, which takes a little getting used to, but is made up for by the steady, comfortable views and resulting ability to discern faint detail.
Step 1
Use the plans available in the supplied zip folder to mark out and cut the various pieces of timber to size.
If you are lucky enough to have a timber merchant who can do this for you, all you need to do is cut the 45° angles with a handsaw.
Step 2
Clamp or tape the wood together to see where screw holes need to go.
Because the triangular shape is inherently strong, only one screw is needed at each joint.
Countersink the holes so the screws sit flush with the surface.
Slightly stagger opposing screws so they don’t clash.
Step 3
Mark out and drill the pivot holes.
Note that the pivot bolts for the mirror sides should be glued in with epoxy resin so they don’t turn in their holes.
After drilling, carefully sand all the parts so they are smooth and fit together nicely.
Step 4
Drill a 2.5mm pilot hole for each remaining screw – this makes it easier to screw in and prevents splitting.
Add a small amount of PVA wood glue to the joint before tightening.
Note the temporary wood spacers to ensure the mirror fork base is horizontal.
Step 5
Test fit your binoculars.
We made our mounting plate from a strip of brass screwed to the binocular mount block.
This needs to be positioned so the front of the binoculars is approximately 110mm from the mirror face, ensuring a clear view of the zenith.
Step 6
Finish the disassembled wooden parts with paint or varnish.
The mirror fork arms are not glued, so the mirror assembly can be removed.
Use four dabs of mastic to glue the mirror to the base.
Add a 12-inch vinyl record and felt pads to complete the pivot.
Mark Parrish is a consummate craftsman who loves making astro accessories
This ‘How to’ originally appeared in the November 2014 issue of BBC Sky at Night Magazine.
Authors
Mark Parrish is a consummate designer and a prolific producer of DIY astronomy products.
