A "parts-only" Labophot included a binocular head with Siedentopf eye tubes broken off and missing:
A 42-33mm step-down ring was ordered; 42-33.8 could have been better..
33mm i.d. threads were ground and scraped away for a tight fit on the filed-flat Siedentopf flange:
most of the debris is from previous brutalities
To minimize debris in prisms, a paper towel was first wadded into the binocular port; later,
compressed air was blown at an acure angle with the port facing down, dislodging debris before wad extraction.
JB Weld will secure the abused 33-42mm ring to Siedentopf flange:
Parfocality is established by first focusing an objective using an intact head,
then swapping this lemonade photo head with a camera and focusing helicoid,
switching between low and higher magnification objectives
while tweaking stage z and helicoid until both objectives focus in the camera LCD.
This hack is particularly handy for Live View with camera bodies lacking flip-out LCDs.
