Hypomnemata

My first epoxy lens and its image at focus

I’ve long been reading telescope maker porn for a while now (I’ve read A Manual for Amateur Telescope Makers twice while commuting), but I have never found the time or place to get down to grinding my own mirrors. I found a few tutorials for grinding coke bottle lenses online over the years, but never got around to that, either.

A couple weekends ago, I did my first experiment with fiberglass. It went pretty okay (read: terrible), but left me with this great little puck of epoxy. Every since, I’ve been wanting to make a lens out of it.

Today, I did. It needs some figuring, and is still quite hazy, but it was surprisingly easy to quickly throw together.  The technique was incredibly cheap and straightforward: first, grind it against 100 grit sandpaper laid on a tabletop to shape.  Then, begin the polishing with a progression of 320, 600, and 1500 grit sandpaper laid on top of a folded rag.  Finally, go after the surfaces with metal polish.  This leaves them a little hazy, but I believe it might be that I wasn’t thorough enough with the intervening sandpapers, so there are still pocks/scratches in the surface.  My loupes are at noisebridge, so I can’t quite tell (and it feels awfully smooth to the touch after the 320).

The technique is still being refined, but it has a lot of promise for banging out toy lenses or custom optical assemblies for art pieces.