Sharing a solution I came up with for bench testing my 83mm F10.8 achromat lens together with my Baader Hyperion 8-24mm Zoom.
I wanted to compare the light path length and focal length with my ASI224MC camera.
Bought two Australia Post mailing tubes, 90mm & 60mm, less than $10
Secure the lens cell in one end of the 90mm tube, camera in the 60mm tube.
Fire up ASIStudio, slide the small tube inside the big one, bring to focus and measure the camera focal length.
Plug in the zoom eyepiece, set to 24mm then 8mm, bring to visual focus and measure.
Very happy with the results, gave myself a pat on the back!
