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!