It’s hard to wait for 3d prints in the mail, so in the meantime, I designed two different parfocal rings. The first is a fixed-height ring that uses grub screws the same as the existing products on the market. 3d printing these is still cheaper than purchasing retail.
The second is a little more radical: a ring printed the exact height it needs to be for a given eyepiece. Binoscope users need these more than anyone, to prevent the need to constantly focus two eyepieces. These rings can be a press fit rather than a grub screw. They can live on their eyepieces. They’re durable, they’re lightweight, they’re stiffer than o-rings. They can be printed really short. They can be printed pretty tall (will need to test). It’s relatively easy to use one set of custom parfocal rings with one scope and another set with another scope.
Anything that can fall in the grass at night should glow in UV light, and that goes for parfocal rings. (Unlike even a very dim visible red flashlight, a UV flashlight is completely undetectable by other astronomers.) Red pigment charges the fastest and has the shortest glow duration, so it seems like the perfect choice.