90deg red dot finder

[Wobbly Bob]

I have these 100mm binoculars with 90deg eyepieces and found looking through the built in sight near impossible. I do not really want to use a large right angle finder as these could upset the balance of the mount plus there is nowhere to mount one, so has anyone any ideas on a red dot finder with a 90deg view ?

[John]

The only ones that I know of are the Telrad which can be fitted with a dew shield / right angle viewing mirror, and the Tele Vue Starbeam which is a £200 plus device.

 

[Geoff Lister]

I have 4 Celestron/Skywatcher scopes with the eyepiece at 90 degrees and the standard RDF at 0 degrees. I have fitted each with a 10mm dia, 1mm thick rare-earth magnet, and can attach a lightweight mirror assembly. The assembly, weighing about 16 grams, is a 40mm square acrylic tile mirror, glued to a small piece of wood (3 saw cuts), and a recessed magnet. The magnets hold the mirror very firmly in place.

I made a couple of others, with 30mm square and round acrylic mirror tiles, but the 40mm gives a better view of the sky around the RDF's tube.

Geoff

[Wobbly Bob]

That is a great solution Geoff. Where did you get the 40mm acrylic mirror from ?

[SilverAstro]

I feel a project coming on

A neat idea by Geoff @Geoff Lister !

@Wobbly Bob :- I have found a 50mm dia on ebay, £1.79+free, 3mm thick,  and there are various other vendors selling sheets,

how easy is this stuff to cut ? Is it likely to cause injury like broken  CDs !!

http://www.ebay.co.uk/itm/Modern-Circle-Acrylic-Mirror-Shatter-Resistant-Round-Circular-Wall-Decor-/191790828034?var=&epid=1756491398&hash=item2ca79fca02:m:mhz8a2hQFvHmFBcNmpVKBaA

Edit later : Hahaa just for a giggle and cloudy nights some star shaped ones :-

http://www.ebay.co.uk/itm/20-Acrylic-mirrored-glass-4cm-stars-mirror-shapes-embellishments-scrapbook-/322134224688?epid=920840584&hash=item4b00b22f30:g:1M8AAOSwjVVVxH43

[Geoff Lister]

Wobbly Bob,

I am sorry about the delay in responding, but I have been abroad, without internet access.

I bought the 3 mirrors, ready cut, on eBay, from "industrialplasticsuppliesltd", for £0.99 each, including p&p.

With my first attempt, I found that the solvent in the contact adhesive, that I used throughout, had attacked the mirror's rear protective layer. This gave a few little spots, visible when looking at the mirror surface, but almost invisible (out of focus) when looking through the RDF at a distant object. For the subsequent mirrors, I used a thin, double-sided sticky, foam pad; without further problems.

It is also worth experimenting with the mirror, before making the diagonal cut on the wooden support. A 45 degree cut should put the red spot in the same direction as the eyepiece; but a small variation in both planes can throw the red dot towards the eyepiece, and so reduce the head movement needed between finder and eyepiece. My 4 RDFs are in slightly different positions, with respect to the eyepiece position, so the 40mm one was cut at about 60 degrees, throwing the dot more towards the front of the RDF body. This worked better on my Newtonian OTA, where the front of the RDF is closer to the eyepiece holder.

Geoff

[Wobbly Bob]

Thank you Geoff for this simple fix, here is my version how ever I had great difficulty in using the RDF due to the fixed position on the binoculars, however I fixed this issue with another simple solution which will be shown in the DIY section.