Concept: Multi-purpose rail mount for piggybacking a Tele Vue 85 refractor onto a Celestron NexStar 8 GPS using the standard Tele Vue clamshell mount instead of the common dovetail plate and rings system. Using the clamshell greatly simplifies movement of the TV85 between the Telepod alt/az mount and the NexStar.
Rail shown with Tele Vue clamshell mount attached.
Design: Wayne Gondella (AFA Telescope and Machine Engineering Services, Inc. of Pittsburgh, PA) designed and fabricated this piece for me - by email, no less. Wayne needed only a few measurements, such as the circumference of the front and rear castings of the OTA, the distance between the two mounting holes on the rear cell, the length between the front cell's single mounting hole and the mid-point between the two rear holes, etc. With these measurements in hand, Wayne went to work.
The rail is completely fabricated from 1/2" 6061-T6 aluminum. Seven holes along the length of the rail yield six possible positions for mounting the TV-85. In addition, four more mounting holes were drilled - two (one each at the front and rear) for mounting a camera with a standard captive bolt, and another two for mounting a Telrad when the TV-85 was not in use. The front and rear radius blocks were made tall enough to hold the rail high enough to allow for my hands to get underneath to attach and tighten the TV-85's two mounting nuts easily - approx. 1-3/4" clearance between the Celestron's optical tube and the underside of the rail.
Wayne gave me three options for the level of finish - natural, finished, and super-finished. I chose the middle option, expecting the rail to have a "nice homebrew" look, which certainly would have been good enough for me. When the parts arrived, I was immediately floored - it far exceeded my expectations with it's near-mirror polish.
Rail plate, radius blocks, and mounting hardware.
Assembled rail mounted to Celestron N8GPS.
Installation and Use : The rail went together easily, all parts showing superb fit. All mounting hardware was supplied, along with printed instructions for attaching the rail to the Celestron. The TV85 works fine in all but the first (extreme aft) mounting position due to the taper of the scope's objective cell; this is not a concern because the TV85 balances best in the third or fourth position, depending on how much weight is hanging off the back of the scope.
As of this writing, the rail awaits fine alignment - weather and work have conspired to prevent me from playing with telescopes of late. Objects centered in the Celestron are just slightly high in the field of view of the Tele Vue, but I believe this is due to the rear radius block being not fully tightened down to Celestron's rear OTA casting.
Nevertheless, having the TV85 on a computerized GOTO mount is wonderful. I've had a couple of opportunities to use the two scopes together for viewing Jupiter, Saturn, and some globular clusters. The misalignment is only an issue if the TV85 is used at higher magnifications, but even at around 150x the object is just slightly out of the field of view - close enough to slew to with little difficulty.
Stacking the two scopes requires counterweighting. I use the Astronomics system on the bottom of the Celestron OTA. The single 2.5 lb. weight is not quite enough, but it is helpful. Additional weights are on my shopping list.
Handy Telrad mounting option.
TV85 and N8GPS.