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Telescope Lunar Photography

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May 10, 2005

Prime Focus:
Attaches camera (without camera lens) directly to the telescope *without* an eyepiece using the telescope as if it's a very long telephoto lens. Requires the appropriate adapter for both scope and camera. With some scopes it's a tube that mounts to the camera that slips into the eyepiece holder. With others (notably some Cassegrain models) the eyepiece holder is removed entirely and replaced with a tailpiece to accept the camera (instead of eyepiece). Magnification at the film plane is determined by the prime focal length of the scope.

Eyepiece Projection:
This is done using an adapter that mounts to the camera instead of a camera lens, holds an eyepiece in it, and slips into the eyepiece holder on the scope. It allows greater magnification than prime focus . . . the magnification being determined by the prime focal length of the scope and the focal length of the eyepiece.

Afocal:
This is perhaps the most difficult . . . in the manner I've seen it usually done. However, it requires nothing more than the scope and a camera as one simply holds the camera (with lens still attached) up to the eyepiece. The difficulty is in focusing the camera and holding it steady enough without bumping the scope either. There are a handful of adapter sleeves that can be used with some cameras and scopes that slip over the camera lens and the eyepiece holder (which requires removing the eyecup from the eyepiece to do this). The ones I've seen are for small digital cameras with small diameter lenses . . . and most of them are home made from black PVC pipe. Lens diameter of a 35mm SLR film camera lens is usually too large to make an adapter practical. Using the filter ring threads on the lens isn't mechanically sound. Filter ring threads weren't made to support the weight of lens and camera body and could strip out of the lens filter ring . . . with catastrophic results to the camera . . . not when it falls . . . but when it hits the ground. I've seen some pictures of a camera on separate tripod set up next to the scope to look through the telescope eyepiece . . . but having done quite a few field macros this seems pretty fussy getting it set up just right . . . and if one isn't fast enough either the object being observed will have moved out of the scope's field, or tracking of the scope will have moved the afocal projection from the eyepiece out of field of view of the camera lens. I also saw a picture of a home-made bracket attached to the scope on which a camera was mounted using its threaded tripod socket . . . it was a pretty healthy looking affair and added a fair amount of weight to the scope.

If you attach a camera to a scope:
Be prepared to adjust the counterweights to compensate for the additional weight of the camera. Some do a little experimentation and set up a preset weight that can be quickly added when the camera is mounted.

One additional method used for wide field is "piggyback." The camera with lens is mounted on the scope tube and aimed in the direction of the scope. The scope is used for maintaining accurate tracking.

If accurate tracking is needed for extremely long exposures, a "splitter" can be used with prime focus or with eyepiece projection. It has a prism inside that splits off some of the light to an eyepiece holder to the side and a special eyepiece with crosshair reticle is placed in it. During exposure, tracking is tweaked to keep the crosshairs on a convenient star in the field of view.

Go to a library and look for Michael Covington's book on Astrophotography. It's a classic and shows how to do all of these things . . . and is considered *the* astrophotography book for the amateur astronomer. It's extremely comprehensive and shows how to make all manner of home-made devices for this as well.

-- John Lind

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May 14, 2005