Perhaps a bit odd and detailed question, but for me it’s interesting to know.
Only the Unitron / (Polarex) 4 Inch equatorial tripod models could be equipped with an -optional- tray light which operated on batteries.
It screwed into the aluminum coloured bottom end of the mount itself.
Threat for this was already provided as standard at the bottom end.
Early models had 62,5 millimeter thread and the later ones 60,0 millimeter.
I don't know in which production year this minor switch of thread diameter was made and why this was done.
The mentioned tray lights also came in these two thread diameter variants.
Now I was wondering if any Unitron / Polarex 4 inch equatorial mount was originally equipped with some sort of a cover cap / plate screwed in on this location if there was not a tray light in place?
Either made of metal or plastic.
Mine (Polarex) does not have such a cover cap / plate (and also no tray light).
It's a later green lens model with 60mm thread at the bottom end of the mount.
The purpose of such a cover plate/cap would be just cosmetical.
Otherwise one would have an open hole with threat.
Not that this disturbs, as you can't see it unless you are looking from below upward.
So it does not bother me, but I feel as a matter of "good quality finish" (something Nihon Seiko was famous for) there perhaps would have been a plastic or metal cap/plate which could be screwed in to cover the hole at the bottom of the mount from the factory?
However, I've never ever seen such a cover cap on any pictures I've seen of 4 Inch mounts, either as a seperate part, or screwed in place when the owner had not specified the tray light. So I somehow doubt if there was any cover cap/plate supplied with these particular mounts when new.
And as many scopes today might have "lost" some parts over the many years of life and use, it's now a bit harder to tell what was original and not regarding these mounts.
I also don't know if there are perhaps any differences in original spec between Unitron and Polarex 4 inch equatorial mounts.
For example, the tray lights were never listed or shown in Dutch Polarex brochures and price lists, so as far as I can tell, the tray lights were never sold new in Holland/Belgium, but I'm not 100% sure on this. (I can't remember having ever seen one when these scopes were sold new back in the '60-80s).
So are there perhaps any 4 Inch (original) owners or other collectors who might be able to shed some light on this?
Edited by C8 Ronald, 11 January 2021 - 08:32 AM.