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Here is some more detail.

A and B are objectives. C is an eyepiece that slides into either A or B. Both telescopes are inverting. If I look at the sun or a distant object and slide the eyepiece in and out Ithe telescope does not focus.

D is a sight tube. It is what I use to take sights.

E is a filter that screws onto  C and D.

F is a lens with male threads on eiher side. The threads are of different diameters.  My guess is that  is to make the image erect. However despite trying just about every combination I can think of I cannot work out how it is meant to be used. I wonder if a tube with female threads at each end is missing, although there are no spare slots in the case.

My questions are therefore:

(a) How do I  get the telescopes to focus?

(b) What is F?

(c) Are the telescopes for sun sights and the binoculars for star sights? Clearly the binoculars cannot be used for sun sights because one half bypasses the sextant filters.