 Quote by PhysicoRaj
Hi, Iam thinking of making my own telescope and I have a magnifying glass lens, biconvex, about 10 cm in diameter and 27 cm focal length. I think it would be better as the objective. For the eyepiece, what type of lens, of what focal length and aperture diameter should I use? (I hope to identify the rings of Saturn.... I may not be able to .. but at least the craters of the moon are okay.)
Thanks.
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The ratio of the objective and eyepiece focal lengths provides the (angular) magnification, so the shorter the focal length of the eyepiece, the greater the magnification. Using a negative (concave) lens for the eyepiece is worse than a positive lens when you are trying to look through the telescope (see Galilean vs. Keplerian telescopes).
http://depts.washington.edu/hssexec/...s_galileo.html
The f/# of your objective is 2.7, so the f-number of your eyepiece does not need to be much larger than 2.7 as well.
This simple analysis completely ignores aberrations, which are likely to be large.