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Hi Steven
I had a Celestron Off Axis Guider lying around so I mated it with my Celestron x0.63 Reducer/Corrector and came up with the following measurements, based on the following assumptions:
Celestron designed their OAG to be used as follows:
Rear Cell of SCT -> 0.63 R/C -> OAG -> T-Ring -> DSLR.
I have a Canon DSLR so in the following example:
Canon EF Mount: distance from the mounting Flange (the metal ring on the camera and the rear of the lens) to the Film Plane = 44mm.
T-mount requires a 55mm Flange to Film Plane distance, therefore T-Ring is 11mm thick.
The 1st attached file shows the Celestron Off Axis Guider mated with my Canon 5D and the Celestron x0.63 Reducer/Corrector (RC).
When the Celestron OAG is screwed into the Celestron RC, the distance between the T-Ring flange and the interface between the OAG Flange and RC Rear threaded Face is 50mm (inside the knurled ring of the OAG).
This gives an overall measurement of 44 + 11 + 50 = 105mm.
Cheers
Dennis
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