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How to Convert a Schmidt Camera to a CCD

A Schmidt camera is a catadioptric telescope used for wide-field astrophotography. The camera (telescope) uses a concave spherical mirror to focus the image being photographed and, as a result, the film must be curved to match the curved focus of the camera. When a charge-coupled device (CCD) is used instead of film to record the image, a field-flattening lens must be placed in front of the CCD to convert the curved focus image into a flat focused image.

Things You'll Need

Plano-convex lens large enough to cover the CCD sensor
CCD camera
Low expansion plastic strips
Silicon glue

Instructions

- 1
  Remove the existing film camera from the Schmidt camera (telescope). The film camera is a simple film roll holder on each side of an open film plan.
- 2
  Glue the plano-convex lens to the CCD sensor frame, taking care to keep the sensor surface clean and free of glue, so that the distance between the lens and the sensor is 1 mm. Depending on the make and model of CCD camera, you may need to build up the border of the sensor using low-expansion plastic strips, to provide the 1 mm of clearance needed.
- 3
  Mount the CCD in the Schmidt camera (telescope) so that the CCD sensor is precisely aligned with the original film plane. The film plane is the location of the exposed portion of the film, when the film camera was in its original place.
- 4
  Calibrate the digital images using the camera software that you use to control the CCD. Depending on make and model of CCD camera and the software being used, several images of different subjects will be required.

Astronomy