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 as it's sometimes called, so it's very hands-on and not the easiest of cameras to use. The custom roll holder eliminates the need to cut the film, but that's only one of the many steps to successfully capturing and displaying an image.
After exposing the film it must be chemically developed. The end result is negative or slide that can be printed on photographic paper or projected on a screen. This is exactly what I did back in the 1970's with my first Schmidt, but I no longer have a darkroom or all the goodies needed to develop film and print photographic prints like I had back then.
And if I want to convert the film to a digital image 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 anymore for every Schmidt image, especially when the end result won't end up being of the same quality as images captured and stacked using a high resolution digital camera.
After exposing the film it must be chemically developed. The end result is negative or slide that can be printed on photographic paper or projected on a screen. This is exactly what I did back in the 1970's with my first Schmidt, but I no longer have a darkroom or all the goodies needed to develop film and print photographic prints like I had back then.
And if I want to convert the film to a digital image 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 anymore for every Schmidt image, especially when the end result won't end up being of the same quality as images captured and stacked using a high resolution 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 Schmidt Newtonian. I'll look at the feasibility of both methods, but 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 are several issues to consider, such as the diameter of the CMOS camera and what percentage of light it would block if mounted internally. Also, possible heat build-up inside the Schmidt from an internal camera could be an issue. Conversely, 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 would ruin the factory focus. 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 the mounting point for the secondary.
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More to come...
Page created 5/28/2023
Last edited 6/19/2023
Last edited 6/19/2023