Sextant - what are these bits for?

[neil_s]

Hi to all - I am new on the site and a relatively new self taught celestial navigator - I've been hooked for about three years, now. There are a couple of things that are bugging me about using a sextant that the books don't seem to answer. I started out with an Ebbco plastic with bits of film negative where the filters should be and got on pretty fine with that. I coped with measuring ie for each observation, and found that multiple shots and averaging would give LOP's pretty close to where the GPS said. Now, I have a rather better instrument. I don't need to average any more, but am puzzled about the choice of filters. The direct sunlight ones I understand, but what are the green and blue ones for? Another thing is the choice of telescopes. I have only a 4X30 on my sextant but I see that a long thin X12 telescope was also offered. What was that used for? I also see that more modern instruments have telescopes with prisms, maybe 7X30. Do these have any advantage over my 4X30? All comments most welcome!

Greetings, Neil. Welcome to the site!  I'm with  this site for not too long but  found it as a treasure box of useful information and expert answers and advices. Can't answer about the filters. I have Astra iiiB sextant and i use zero magnfication sight tube. I found it much  more useful than any magnification telescope because , the way I experienced it, it was very difficult to keep  the object of observation steady. Magnification kind of affected it.  With zero tube I didn't have this kind of problem. I've read somewhere that those filters are used for some specific conditions. Not sure about the source,, kind of vague recollection.  Best regards

Thankyou for your comments, Rumata. I also made a site tube for the Ebbco sextant and found it good for Sun sights. I find I need some assistance, though, to see the stars. My eye-sight is not as good as it was. That's my justification for buying the Tamaya!