Re: ATM Making eyepieces

["Betsy or Mike Marchand" <bmarchan@mnsi.net>]

Hello,

>Is their a way too (cheaply)
>make one's own eyepieces ?


 Yes. I used to make my own Ramsden eyepieces for around $3 each. Do you
have access to a quantity of plano-convex lenses?

If you can find a cheap supply, you need two identical lenses for each
eyepiece. The simplest arrangement has both plano surfaces facing outward,
convex surfaces facing together inside.

Classically, use 2/3 times the focal length of the lens as seperation.

You want to know what will be the effective  focal length of the
combination?
It is 3/4 times the focal length of a lens.

Example: I purchased two identical 22 millimeter diameter plano-convex
lenses of 36 millimeter focal length.

Seperation between convex sides of lenses = 2/3*36 =24 millimeter
Effective focal length =3/4*36=27 millimeter.

You need to know what diameter of lenses to buy to avoid vignetting?

I made a scale diagram of the entire telescope (including light rays) and
drew in the eyepiece a distance equal to the effective focal length past the
focal plane formed by the telescope. The lens diameters were drawn to the
same scale as the rest of the scope.

For reference, see one of Sam Brown's books:
1) All About Telescopes or,
2)Telescope Optics
especially if you are going to try designs for higher powers of
magnification or scopes faster than about F/8...

Hope this is clear, and that you can find a quantity of lenses cheap!

 - mike