Common Schmidt Camera Errors

There are a number of simple mistakes that can occur after late night fatigue interferes with the operation of a Schmidt camera.

The Celestron Schmidt uses two different film holders that position the emulsion at the exact focus of the camera, one for white light photography, and the other for photography with filters. The filter material slightly shifts the focus of the camera, thus the filter film holder is machined slightly different to take the focus shift into account. The only way to tell the two film holders apart is a flat washer under the film holder pressure plate on the filter film holder.

In the dark, especially when it is cold in the dead of winter, it is easy to overlook or simply not be able to feel the identifying flat washer on the Schmidt's filter film holder. Unless the two different devices are separated, you might use the wrong film holder. Using the filter film holder without a filter, of the nonfilter film holder with a filter, will result in the discovery of the Donut Cluster. This amazing star cluster seems to be composed entirely of ring-like planetary nebulae that are really out of focus stars.


Another Schmidt trick is catching the felt lib of a film cassette between the frame and pressure plate of the Schmidt film holder. This causes half of a 45-minute exposure to be out of focus after you just froze your bodily appendages off guiding the camera on a cold winter's night.


Schmidt trick number three is to use a roll film adapter and wind the film in the wrong direction, double exposing the previous shot. One can imagine Halton Arp's delight when he is presented photographic proof that M-31 and M-33 are in collision!


Another persuasive argument for switching hobbies to stamp collecting is to complete a half-hour Technical Pan exposure of the Butterfly Nebula near Gamma Cygnii then find the red filter has popped off the film holder and is laying on the Schmidt's mirror.

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