If you have ever been in a camera store, you may have seen a used equipment section. As digital cameras become more advanced, this section has become filled with older manual telephoto lenses. Although these lenses collect dust in a used camera equipment case, they can still be useful. Used camera zoom lenses, long fixed focal length lenses and mirror lenses may be converted into telescope lenses with the correct equipment.
Locate a monocular converter. There are several companies that manufactured monocular converters including Pentax and Minolta. Many of these products may be found in used camera equipment stores, ordered new from back stock equipment at camera supply stores or purchased from online auction houses. Because many companies no longer make monocular converters, you should locate a monocular converter before purchasing used telephoto lenses.
Acquire used telephoto lenses that will fit your monocular converter.
Attach a monocular converter to your telephoto lens. Most newer American-made monocular converters have a bayonet mount. A few older converters attach by being screwed onto the camera lens.
Place the back lens cap of a telephoto lens facedown on a work table.
Center a PVC pipe adaptor end-down onto the back of the lens cap. Trace around the inside of the adaptor with a marker.
Drill out the area that you have marked inside the back lens cap.
Place a layer of glue onto the end of the PVC pipe adaptor. Place the adaptor end-down onto the back of the lens cap so that the inside of the pipe aligns with the hole you have drilled in the cap. Allow the glue to dry before continuing.
Cut a section of cardboard from the paper towel tube that will fit inside the plastic PVC pipe fitting. Line the PVC fitting with the cardboard.
Insert the push-fit eyepiece into the PVC tube so that it rests inside the cardboard.