TeleVue 32 mm Plossl filter thread

[Solanum]

For some reason, my TV 32 mm seems to have a different filter thread from my other eyepieces. My Lumicon nebula filter falls straight out of it, whereas it screws into all my other eyepieces. I'm confused, is there a reason for this?

[Profiler (Profiler)]

Check the threads on both the Plossl and filter for possible damage

I have noticed that the threads on some filters do not perfectly match - my Baader filters were fine but astronomiks wouldn't go on perfectly

[Don Pensack]

You've run into +/- tolerances.
The Tele Vue is cut a bit larger and the filter a bit smaller.
Eyepieces vary in size (and by more than you would think), so a filter manufacturer would tend to want to cut the size a bit small in order to fit, say, 80% of all eyepieces easily.
Eyepiece manufacturers, on the other hand, would want to cut the threads a bit large so that 80% of all filters would fit.
Add manufacturing tolerances and you have a poor fit.

Here is what you can do, and it will help:
use a small model-painting brush to paint the bottom threads on the TV eyepiece flat black. This won't damage the eyepiece--one could even argue Tele Vue should have done that already. It will essentially reduce the inside diameter of the eyepiece a tad.

And, hopefully, though the filter will be loose thereafter, it will snug up at the bottom of the threads to fit tight enough to stay on.

Many Korean filters (notably those from Orion in the US) have a slightly aberrant thread that doesn't thread in more than a thread or two.
But other filters have the usual threads--but, as you found, vary in size a bit.

[Solanum]

Originally Posted by Don Pensack

You've run into +/- tolerances.
The Tele Vue is cut a bit larger and the filter a bit smaller.

I guess so, this is a big difference for +/- tolerance though. Filters fit other eyepieces better or worse (including other TV eyepieces), but don't fall off, so I am surprised this is so big a difference. Doesn't catch in the thread at all. I bought this eyepiece new a couple of months ago, whereas my other TV eyepiece was second hand and is older (as is the UHC filter I was using and several of my other EPs). I wondered whether standards have changed.

Originally Posted by Don Pensack

Here is what you can do, and it will help:
use a small model-painting brush to paint the bottom threads on the TV eyepiece flat black. This won't damage the eyepiece--one could even argue Tele Vue should have done that already. It will essentially reduce the inside diameter of the eyepiece a tad.

This is a great idea, I think that's what I will do!