| Bargain hunter's delight: How much for a small, compact, used 500mm f/8 mirror lens? Anywhere from $60 up. Any good? Better test it.|
1-Call photo stores and ask for the Used Equipment department. Inquire about the availability of mirror lenses in the 450-600mm range.
2-If possible, go to the store with your camera body to examine lenses yourself. You can probably try lenses right there and maybe even shoot some test pictures at the store.
3-If an in-person visit isn't possible, ask the salesperson to describe lens by phone: indicate its size, weight, close-focusing capability, price, warranty, and shipping and handling costs. Check on the price of a T-mount for your camera. Make sure you can get a money-back guarantee.
4-When you receive the lens and T-mount, attach them together and then to your camera body. If lens scales are not at top, loosen three T-mount screws with a jeweler's screwdriver. Turn lens so scales are upright on camera, tighten screws.
5-Make a quick, simple lens test: On a bright day, load camera with ISO 400 print film. Find a set of buildings or a scenic with details at infinity that appear at the center and edges in your viewfinder. Place camera and lens on a suitable tripod or other support. Focus carefully on subject using camera focusing screen. Select aperture-priority autoexposure. Ask your photofinisher for an 8x12 enlargement. Examine sharpness at center and edges. If the sharpness pleases you, keep the lens.
6-Alternatively, make a more precise lens test: Load up with ISO 100-200 fine-grained slide film. Find a detailed building façade at least 25 feet away that is parallel to your tripod-mounted camera's film plane. Shoot as in 5. Now, change lens and mount one of your non-mirror lenses that you know to be sharp. Approach the building until you frame the same view as the one you shot with the mirror lens. Make an aperture-priority exposure at f/8. When slides are processed, compare results using a 10X or greater magnifier. Quality of mirror lens photo should approach picture made with your non-mirror lens. But don't expect the mirror lens picture to equal it.