A Small Refractor
One for the Kids
I built a small refractor for my youngest daughter, the techniques are applicable to other small refractors for finders and such. Because it doesn't use a real cell with adjustments and the focuser design slips a bit, it is not useful for more elaborate applications. It does have the advantage of being able to be built in a few hours for a few dollars. The PVC parts make it almost indestructible, which is perfect for a childs telescope. I have tapped a 1/4-20 hole at the approximate infinity CG (it changes whether the focuser extension) to mount it to a small camera tripod. This is important because it is hard for even an adult to hold a 19x scope steady for any length of time. You can easily make out Jupiter's moons in this scope, and in still air you can just see that Saturn has rings, rather than little bumps on each side. But what most kids love is looking at the moon, particularly in early crescent phases.
The Bits and Pieces
The Hardware Store Stuff
Check the corner of the basement, you may already have a lot of this stuff, if not you can get it all at the hardware store (for under $10).
The Objective Lens
I picked up the optics at Surplus Shed. They have tons of this kind of stuff and are really nice people to deal with to boot. I came across a particularly nice bunch of 48mm diameter 380mm FL lenses that seem well corrected. They are surplus and some have so-so coatings, but for $7 they are well worth it. There are other surplus optics dealers and don't overlook yard sale binoculars as potential objectives.
A Simple Lens Cell
An Inexpensive Eyepiece
This was a projection lense with a zoom barrel (20-32mm). Because it has to be turned "backwards" to use as an eyepiece, I sawed off the end and glued it to always provide its shortest focal length (20mm). The prototypes I tried to leave the zoom on never worked well enough to be worth the extra effort, you might have better luck.
Details and Assembly
The Focuser
MAIL ADDRESSES:
WORK: omalleyj@dialogic.com
PLAY: omalleyj@eclipse.net