Does anyone know of where I can get a 50mm skylight or uv filter. I'm trying to protect the front element of a Horseman Universal Finder which appears to be an odd 50mm (49mm is definitely too small by the slightest bit). 50mm appears to not be a conventional size and I'm having a hard time finding anything. Wondering if I may be missing some brand designation that would turn something up.
Being a finder and not a lens it's not likely to be designed to use filters .
The thread your looking at will be for the retaining ring to hold the front parts in the barrel .
If you want to protect it while it's not in use , use push on caps that slip on the outside as you would binoculars or telescope eyepieces .
Alternatively you could use a clip on filter , or have a firm make you a step up or down ring to allow you to mount a standard size filter .
SRB Gritturn in the U.K , or Grimes in the US .
You'll need to confirm the thread diameter and pitch if you doing that though , so you might need to take the retaining ring out to measure.