they should not be made the same. Furthermore, when the warping harness is placed on the secondary mirror (see "The Mirror Warping Problem," ahead) other conditions dictate that the secondary mirror blank should be nearly the same size as the primary. If we make the two mirrors the same diameter and the same radius of curvature, then one grinding tool and one pitch lap will suffice for both. This represents an appreciable saving in time and expense in constructing the telescope and is, therefore, recommended. If R1 and R2 are replaced by the single quantity, R, and T is made equal to 1.28S, Eqs. (2) through (6) reduce to the following:
Theoretically, the primary mirror should be a paraboloid, and the secondary, an hyperboloid. Both
mirrors have such long radii of curvature, however, that neither one deviates very much from a perfect
sphere. In Yolo reflectors of small aperture and moderately long focal length, this deviation is
practically undetectable, and instruments employing spherical mirrors will show no need for correction.
However, instruments of eight-inches aperture or larger, made with spherical mirrors, will be found to
be under-corrected by an appreciable amount. This defect can be eliminated by a small amount of
parabolization applied to the primary mirror only.