Updating a Celestron 5-1/2" Schmidt Camera
The 5-1/2" Schmidt is designed to use 35mm film to take astrophotos. However, the standard film holder only holds a single cut frame, or chip, at a time, so it's very hands-on and not the easiest of cameras to usee. The custom roll holder eliminates the need to cut the film, but that's only one of the many steps to successfully capturing an image.
After exposing the film it must be chemically developed. The end result is negatives or slides that can be printed on photographic paper or projected on a screen. This is exactly what I did back in the '70's with my first Schmidt, but I no longer have a darkroom and all the goodies to develop film and print photographic prints that I had back then.
And if I want to convert the film to digital for post processing then the negative or slide has to be scanned. I'm not sure I see myself having the time and inclination to go through all this for every Schmidt image I capture, especially when the end result won't be of the same quality as an image captured directly with a high res digital camera.
After exposing the film it must be chemically developed. The end result is negatives or slides that can be printed on photographic paper or projected on a screen. This is exactly what I did back in the '70's with my first Schmidt, but I no longer have a darkroom and all the goodies to develop film and print photographic prints that I had back then.
And if I want to convert the film to digital for post processing then the negative or slide has to be scanned. I'm not sure I see myself having the time and inclination to go through all this for every Schmidt image I capture, especially when the end result won't be of the same quality as an image captured directly with a high res digital camera.
The camera is about 2-feet long and 6-inches in diameter. The door on the side is for accessing the spider assembly to load and unload the film holder. The two options for mounting a CMOS camera are either installing it in place of the film holder or adding an elliptical secondary mirror to turn the camera into a Schnmidt Newtonian. I think I'm leaning towards the first option, but I'll look at the feasibility of both, and either way will require modifications.
I really don't want to make any irreversible mods to the camera, so I need to give this a bit of thought before I start removing parts from the Schmidt. There's also several issues to consider, such as the diameter of the CMOS camera and what percentage of light it would block if mounted internally. Plus possible heat build up inside the Schmidt from the camera could be an issue. Mounting the digital camera externally would eliminate the above issues, but requires an elliptical secondary mirror, and enough focal distance to clear the housing and allow for a focuser. And in both cases there is also the issue of the Schmidt's curved focal plane. Using a smaller sensor that captures just the center of the field-of-view, and using a CMOS chip with small pixels, should both help. Also adding a field corrector lens in front of the sensor could help eliminate the curvature. |
To make room for a CMOS camera and focuser inside the Schmidt would mean modifying or removing the existing spider assembly. Removing the spider and designing a custom replacement would be less destructive. But the custom spider will need to be built first, before removing the original assembly.
Installing an elliptical 45° mirror to create a Schmidt Newtonian would not require removing the spider and might be simpler. The spider could be used as a mounting point for the mirror. |
More to come...
Page created 5/28/2023
Last edited 6/19/2023
Last edited 6/19/2023