MDM Observatory's 8K CCD array project:


Telephone: (212) 854-7899


Moving forward from the focal plane, containing the CCDs, one encounters a fused silica vacuum window, the wide-field corrector, shutter, filter wheel and guider assembly. From the focus of the naked Ritchey-Chretien f/7.5 telescope to the back surface of the instrument rotator, there is a distance of 412mm to accommodate these components along the optical axis (elongated by 3.1mm due to the effects of the corrector.) Since the current MIS must be removed due to its constriction of the field of view of the telescope, some of its components: guider and filter wheel, must be replaced. No filter wheel currently at MDM is large enough for this purpose. Since the instrument is likely to be used ultimately on the 1.3-meter McGraw-Hill telescope at MDM, the guider should easily accommodate this change in telescope, as well as easily interface with existing guider telescope control hardware and software. Likewise, the corrector performs reasonably well on the 1.3-meter (treated elsewhere).

The basic components of the 8K system are divided into several separable modules: CCD imager, corrector, shutter, filter wheel, guider, empty spacer module (perhaps to be replaced later with a module containing spectrographic hardware for a wide-field spectrograph which could be swapped for the imager. This spectrograph is speculative at this point.) Riding on the instrument rotator with the components mentioned above are the dewar and liquid nitrogen reservoir, preamps, amps, control electronics bay and digitizing electronics bay. These are attached by a long cable run to a Sparc control computer, hard disk and tape drive farm.

Sketch of Basic Components near Optical Axis:

The positions shown here are approximate. The "Telescope Backplane" is the back of the instrument rotator. Not shown here is the 3 degree tilt of the two guider assemblies (pick-off mirror, corrector and guider cathode) to conform to the deviation of the focal surface from a plane. The guider corrector is a tilted flat that cancels astigmatism. The assembly and concept sketches for the shutter / filter wheel / corrector / focal plane + dewar + controlers are shown below.

Concept Sketch of Basic Components, Shutter to CCD Dewar (reduced 50%):

Assembly Sketch of Basic Components, Shutter to CCD Dewar (reduced 50%):