OK, I see what you're looking at....
For the purposes of the comparison graph, the "zero" position shown is based on:
(Imaging through a DSLR with the Powermate™ T-Ring Adapter and camera T-Ring — without added extensions — brings the focus position to 0mm.)
which would bring the focal plane (the camera chip) to 55mm above the T-ring adaptor.
If you use the T-ring adaptor and connect directly to the camera (ie ASI 174 etc) the chip would lie 17mm above the T-ring adaptor.
This would be at minus 38mm on their graph......
I think the data is missing
