Brackets and adapters

A "camera adapter" for a telescope can be any of a wide variety of gadgets, depending on the kind of camera, the kind of telescope, and the way you want to couple them.

Piggybacking is simplest because all you have to do is mount the camera on the outside of the telescope. Larger telescopes have predrilled holes for piggyback brackets. With smaller telescopes, including the NexStar 5 and ETX-90, you have to attach the camera with a strap, easily made from a drainpipe hanger or a large hose clamp. You can even mount a camera on the counterweight of a German equatorial mount.

There are three ways to do afocal coupling. You can support the camera on a separate tripod - which looks clumsy but is marvelously free of shutter vibration. Or you can use an afocal adapter. This in turn may be either a bracket that supports the camera by its tripod socket, or a cylindrical device that grips the eyepiece and screws into the front of the camera lens like a filter. Afocal adapters are available from ScopeTronix (1423 S.E. 10th Street, Unit 1A, Cape Coral, FL 33990, http://www.scopetronix.com) and LensPlus (11969 Livona Lane, Redding, CA 96003, U.S.A., http://www.lensadapter.com) among others.

Figure 7.3 shows how direct (prime focus) coupling is done. The camera body accepts a T-adapter (T-ring), which has 42 x 0.75-mm threads that accept other

Camera

Camera

42 x 0.75 mm

24 threads/inch

Figure 7.3. Direct (prime focus) adapters for ordinary telescopes (top) and Schmidt-Cassegrains (bottom). T-adapter is chosen to fit lens mount on camera.

24 threads/inch

Figure 7.3. Direct (prime focus) adapters for ordinary telescopes (top) and Schmidt-Cassegrains (bottom). T-adapter is chosen to fit lens mount on camera.

accessories. (These T-adapters are all that is left of a universal lens mount system that was popular in the 1960s but died out when lenses began to require aperture coupling.) Negative projection is done with the same adapter, with a Barlow lens between the adapter and the telescope or a teleconverter between the T-ring and the camera.

Adapters for eyepiece (positive) projection are similar but larger, with space inside for the eyepiece. They do not fit large wide-angle eyepieces.

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