Mechanical Design - Collimation
The Ceravolo Astrograph offers one major advantage over other high-end Cassegrain telescopes - ease of collimation. Unlike a typical aspheric Cassegrain secondary, the astrograph's spherical secondary has no discrete optical axis, and does not need to be precisely centered relative to the primary. Moreover, the primary mirror is pre-aligned with the field corrector lenses and bonded in the 6-point flotation cell. Therefore, collimation of the Ceravolo Astrograph requires only simple tip/tilt adjustments of the secondary mirror. Final collimation is achieved under the stars: an image is taken and the star shapes at the corners of the field examined. The secondary is adjusted until the stars are of a uniform size across the entire field of view.
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A great deal of effort was expended developing the primary and secondary mirror cells. The aim was to make high finesse collimation a simple procedure. With an optically fast system, we found that a conventional secondary mount was inadequate to achieve the tightest possible images across a large CCD. The Ceravolo Astrograph's advanced design features ultra-fine, 80 threads per-inch screws for collimation. The orthogonal, or left/right and up/down collimation screw adjustment method removes the often-frustrating guesswork associated with typical 3-point adjustment cells. And the heavy-duty spider is bolted to the aluminum end ring to avoid flexing the carbon tube. |