While the simplest way to do this would be via an Olympus Photomicro Adapter L and an eBay OM-to-EOS mount adapter, I decided to assemble my own to allow for a couple of characteristics I really wanted. The two things that were desired were...
1) The ability to smoothly rotate the camera 360 degrees, and if desired lock it in position
2) Have a very fine height adjustment so that it is easy to adjust the camera height in order to make the viewing eyepieces and camera very accurately "parfocal"
So here is the result. As marked on the lower picture the pieces used were:
A) An Olympus clamp scavenged from an old Olympus camera part.
B) A very nice custom piece made for me by our own member, and a relatively close neighbor "elf" (Thank you Ed!). This piece is attached via 4 machine screws to the part A. It then provides me with a standard "T-thread"
C) A Baader VariLock T-extension tube. This is a finely threaded variable extension tube with locking ring. It has a male "t-mount" on one end and a female "t-mount" on the other.
D) Blue Fireball Eyepiece Holder (2"), ("Visual Back"). (From Agena Astro Products)
E) Blue Fireball ELIM-T 2" Prime Focus Camera Adapter (From Agena Astro Products) This piece has an attached EOS mount and a nicely machined sleeve, about 50mm long, that fits very smoothly and precisely into the visual back (Part D). It allows for very smooth 360 degree rotation, and can be locked via thumbscrews on the visual back.
