Coupling Gear
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Attaching a camera to a Questar telescope is relatively straightforward. With its lens removed, the camera body connects to a rear axial port via a coupling and, if necessary, a lens mount adapter. In line with the telescope’s central axis, the camera’s light recording medium receives light directly from the main optics. The telescope in effect becomes the camera’s lens.
With the internal diagonal disengaged (i.e., moved out of main light path), the photographer has use of the Questar’s finder system to aim scope coarsely before fine-tuning that aim in the camera’s viewfinder.
Couplers
For the first decade of production, the Questar’s rear axial port had the same dimensions as the top port used for visual observing. All that was necessary was a camera coupling set that was no more sophisticated than an additional eyepiece adapter tube and a coupling adapter plate with M42 x 1mm universal screw mount lens threads, which were commonly found on several SLR camera makes of the 1950s. Since both Praktica and Pentax cameras had this type of lens mount, some referred to this style of lens mount by those names.
In early 1964, Questar introduced an updated swivel coupling set at the same time that it brought its wide field construction to the market. The dimensions and threading of the rear axial port now matched the top of the Questar’s eyepiece adapter tube. In fact, one could now attach one of two threaded eyepieces directly to the rear port for straight-through axial observing without having to use an additional eyepiece adapter tube.
Adapters
Since its earliest days, Questar has not changed the dimensions of the camera coupler’s receiving threads. Even today, they continue to be the same M42/Praktica/Pentax/universal screw mount threads one found on the earliest camera coupling set.
The best way to attach any kind of camera either film or digital is to obtain a lens adapter with female M42 x 1mm threads on the lens side and whatever lens mount is appropriate for the camera on the adapter’s other side.
If such an adapter is not available for a particular camera, another possibility is to obtain a T-ring adapter (0.75mm thread pitch) that is appropriate for the camera being used. An additional adapter with T-ring threads on one side and the coarser M42 x 1mm threads on the other side would also be necessary.
For more information, see two helpful articles entitled “Camera Adapter Threading” and “Camera Connection” on Rob Pettengill’s website.
Extension Tubes
Extension tubes increase effective focal length and thus magnification, and they also reduce vignetting. They accomplish this at the cost of increasing focal ratio and exposure times.
Especially with heavier camera bodies, another consideration to keep in mind is the significant increase in the amount of force the weight of the camera body exerts as it hangs at a greater distance from the rear of the telescope.