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Thanks for the explanation. I just took some measurements:
Height of 2” Powermate with 2”-1.25” adaptor removed = 119mm (with bottom cap on).
Height of 2” Powermate with upper visual piece removed and replaced with a T-RING FOR TELE VUE 2X POWERMATE (printed on side) = 73mm (with bottom cap on).
Difference is 43mm. With the Tele Vue T-ring option you simply attach the T-Mount adaptor for your DSLR to the T-ring.
If not using the Tele Vue T-ring adaptor you connect the camera body T-mount adaptor to a 2”-T2 adaptor and slip this into the 2” visual part of the Powermate. The DSLR ‘film’ plane is then 43mm further back (plus thickness of 2”-T2 adaptor, these days quite thins at approx 3mm), than if using the Tele Vue T-ring.
I’m not quite sure I fully understand the Tele Vue graph. They label it FOCUS POSITION FROM TOP SURFACE, but is that from top visual surface or top t-ring surface?
Anyway I’m not an imager and just dabble in the occasional lunar eclipse photo through my ED80 or TV-101. I too have all the Tele Vue adaptors and Powermates mainly for visual. A 35mm Panoptic with 4x Powermate makes an outstanding (but very heavy) 8.75mm eyepiece with huge eye lens and plenty but not too much eye relief.
To the OP. Powermates do come up for sale in the classifieds but sell usually reasonably quickly (depending on asking price of course).
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