I have a question that may not strictly belong in this forum as it relates to modifying a commercial mounting, but my one of the main parts of the question relates to generic optics so I'll post it anyway.
I have a Celestron Ultima 8 SC. One of the things I don't like about observing with it (although all scopes I used have the same problem) is the contortions I have to put my body through to locate and view objects in diverse parts of the sky. Sometimes I have to kneel, sometimes to stand and sometimes it seems the best thing to do might be to lay on the ground. This is not only a problem for me, but for "the public", especially kids, when our club hosts star parties.
I am considering modifying the mount to allow comfortable viewing from a single position no matter where the scope is pointing. I expect my design is not unique but I don't know what its name might be; I'll describe it here.
Basically, I plan to replace the fork mount with a modified german equatorial.
I plan to remove the existing fork mount and use the existing clock drive, etc. as the polar axis. A rectangular platform will be attached to the axis drive housing in place of the fork arms. The declination axis mechanism will be attached to this platform. When viewing, the observer will sit with his/her back to the north an look directly down the polar axis toward the south celestial pole. (This is the opposite direction that is used with the aligning scopes in the polar axis of some german equatorials.)
One of the major mods involves the declination axis. In most german equatorial the declination "axis" is a solid steel rod; in my design this axis is a 2" hollow tube with external bearings. The scope's tube assembly will be fixed to this axis and a corresponding 2" hole will be made in the tube itself. A new diagonal mirror will be placed on the scope's optical axis to reflect the light from the secondary on the corrector plate out the side of the scope and through the declination axis tube. No matter what the declination orientation, the image will be sent out the declination axis instead of down the original baffle tube.
The declination axis tube will be fairly short (but long enough so that the observer will not be in the light path when the scope is pointing toward the celestial north), and will be supported by external bearings. A second diagonal mirror will be fixed to the support platform directly over the polar axis and will reflect the image toward the north celestial pole into the eyepiece. This second diagonal and the eyepiece will rotate with the entire platform around the polar axis but are not connected to the dec. tube.
With this arrangement, the observer sits in comfort, looking down the polar axis into the eyepiece no matter what dec. and RA the scope is pointing at. (Of course, as the dec and RA are changed the image will undergo some interesting rotations from the observers perspective).
I realize that dimensions will be critical, and counter-balancing etc. will have to be done.
My questions relate mostly to the optical issues, including:
Has anyone done this before? (Does this kind of a mount have a name?)
I'm assuming the additional diagonal mirror needs to be only the diameter of the current current tube...is this correct?
I'm assuming the dec. tube will have to be baffled to reduce light scatter; is there some other source of light pollution problem inherent in the design?
Other that the need two use two diagonal mirrors does this design present any specific optical degradations
Are there any other mods I could make to improve the design?
Am I crazy?
TIA,
Terry Chrisman