Distanceviewers rely on two or more convex lenses to focus light from a distant object onto the eye. Although other parts of the distanceviewer are important to its overall effectiveness, the quality of the lenses ultimately determines the usefulness of the distanceviewer.

The first step in making a distanceviewer lens (or, alternately, a lens for a pair of eyeglasses) is to select a glass blank from which to grind the lens. It should be round in shape, but doesn't have to be, and the glass should be flawless, else the lens will not work properly. The glass blank should be at least as thick as the thickest part of the double convex, and preferably thicker. Use the principles of optics and the type of distanceviewer required to determine the dimensions of the lens. Secure the glass blank to a working surface. Make sure to have a pitcher of water nearby to help cool the glass as it is being shaped and also to wash away the residue.

Use a grinder to rough out the shape of the lens. Keep it as parabolic as possible while grinding, but it doesn_t have to be perfect. As the glass heats in the grinder, keep it wet (if it gets too hot, it may warp). After the blank is ground into the roughly double-parabolic shape, use fine sand to finish the shaping. It is important to have a keen eye at this point, and be careful not to over-shape the glass. Double-curves ruin the lens.

Once the lens is nearly completely shaped, wash it off well with water, being careful of the glass splinters. Then, use a rough fabric (perhaps burlap or roughened felt or horsehair cloth or even steel wool) to smooth out the surface completely, removing all the ridges and marks. Use the fabric (and also sand or grinding, if necessary) to finish off the edge of the lens, as well.

Congratulations! You now have a lens. Unfortunately, this is a trial-and-error process, and many lenses come out imperfect, don't work, and have to be remade. Good luck!