Greg's Right Angle Telrad (Finder)


While at the Oregon Star Party this year (2011) I found it uncomfortable to twist my neck to look up through the Telrad so I decided to convert my Telrad for right angle viewing.  My first attempt was to mount a 45 degree angle mirror below the Telrad.  I built a mock-up out of cardboard.  It worked but it was bulky.


At a (Rose City Astronomers) telescope workshop Greg Jones suggested that I consider using a beamsplitter mirror instead of the 45 degree mirror.  Greg's idea is simple and elegant.  I attached the beamsplitter mirror to the under-side of the Telrad window with blue painter's tape.  Notice that holding your eye closer to the mirror results in a larger field of view.


The beamsplitter mirror cost 50 cents at (plus $5 for shipping).  The mirror reflects 75% of the light and the image is reversed.

Alternately, the beamsplitter mirror can be attached on the top of the Telrad window.  

  • Pro:  Light from the stars reflects directly off the mirror instead of passing through the Telrad window twice.  

  • Con:  The blue tape covers some of the beamsplitter mirror and the mirror is susceptible to fingerprints and dew.


Whether the beamsplitter mirror is attached to the top of bottom of the Telrad window, this is an inexpensive way to convert your Telrad for right angle viewing.


Some of my astronomy projects:

12.5" F4.5 String Telescope       
String Telescope Concepts     
8" F6 Stacked String Telescope (Successfully built)    
Flex Ring (Flexible upper ring used with four strut string telescope)   
Truss Tube to String Telescope Conversion