Seymour Rosin

Optical System for Large Telescopes

An optical system composed of a large primary mirror and a closely spaced two-element lens system in the convergent beam delivers a high-quality image over a flat field of appreciable size. The mirror is hyperboloidal in form.

A New Thin Lens Form

A general qualitative analysis of the aberrations of a thin lens system is given and applied to a triplet lens form which is quite flexible in adjustment of those aberrations which are capable of being varied in thin lens systems, particularly with regard to the axial secondaries, zonal spherical aberration, and sphero-chromatism. In its highly corrected state the lens form, of which three general examples are given, may be made to fulfill the conditions of Fraunhofer and Gauss at high relative apertures with mild curves and insensitive spacing.

Still More on Afocal Parabolic Reflectors

Seymour Rosin 94 Laurel Drive, Massapequa, New York 11762. Received 23 May 1974. I welcome Annables addition to the prior art on the afocal parabolic reflectors. A private communication from R. A. Buchroeder includes a description of the Mersenne telescope. I apologize to Gascoigne for having overlooked his reference. On the other side of the coin, many of my colleagues have been unaware of these systems. In particular, a recent excellent theoretical review of two-mirror aplanats seems to have overlooked them completely. As Annable points out, afocal paraboloids are useful as well as elegant, and their application need not be related to astronomical problems.

Extending the Stellar Field of View of Ritchey-Chretien Telescopes

The preferred modern type of large telescope today is the Ritchey-Chretien form. The field size is aberrationally limited by undercorrected astigmatism and field curvature. A pair of equally and oppositely oriented flat transmittng plates can neutralize either or both of these aberrations locally in the field to restore the image. These plates, relatively inexpensive and positionally noncritical, may be used to extend the available image area by an order of magnitude.