Comparison of lens and Fresnel null correctors.

Fresnel null correctors are compared with classical Offner and Hindle null correctors for both optical performance and system sensitivities to errors of construction and placement in the test setup. Fresnel null correctors are closely related to circular diffractive null correctors, the main difference being that a Fresnel uses tilted grooves functioning like a blazed diffraction grating. The Fresnel has an advantage in that specific power terms can produce an aspheric wave front directly and not as the byproduct of bending lenses as in the traditional lens null correctors. The parametric relationships are summarized for a range of configurations of lens null correctors and for Fresnel null correctors. The sensitivities to construction and deployment errors are presented for each of these examples. The performance of two Fresnel correctors for an autocollimation test of a full three-mirror Cassegrain configuration is presented.

Spherical primary telescope with aspheric correction at a small internal pupil.

The aspheric plate at the center of curvature of a spherical primary is replaced by a small aspheric corrector at a minified pupil located inside a reimaging camera. The correctors are identical for each reimaging camera because the spherical aberration of the primary sphere is identical and symmetrical for all field positions. The magnitude of the field aberrations is evaluated over a range of primary focal ratios and minified pupil diameters. The major term is the increased field angle through the minified aspheric corrector. The field and chromatic aberrations in such a camera are compared with the equivalent full-aperture Schmidt corrector. Field-of-view partitioning enables each subfield to be designed for specific observational requirements, such as multiple-fiber spectrography or CCD imaging. Field partitioning is shown to be a powerful means for the replacement of the large aspheric corrector of a Schmidt telescope by a multiplicity of small reimaging subsystems. The cost to fill the typical wide field of a Schmidt telescope with reimaging modules is approximately 1% the cost of a Schmidt aspheric plate.

Determination of the Hubble Space Telescope effective conic-constant error from direct image measurements.

Direct measurement of discernible features in the Hubble Space Telescope (HST) imagery has enabled a self-consistent determination to be made of the effective conic constant of HST images taken with planetary camera 6 (PC-6) of the wide field and planetary camera. Before being corrected for the contribution from PC-6, the conic constant is - 1.01429 +/- 0.0002. The correction for PC-6 is less accurately determined but probably lies between -0.0002 and 0.0004. As a result the HST optics are characterized best by a conic constant of - 1.0140 +/- 0.0003 as obtained from direct image measurements.

Optimum solution for spherical primary mirror with two and three aspheric corrector plates located near focus. Part 2.

The case for two aspheric plates is further investigated to include ray trace evaluation of various solutions, removing the possible two solution regions noted in Part 1 [Meinel and Meinel, Appl. Opt. 20, 3627 (1981)]. The study is extended to include one reflection plus one transmission aspheric and two reflection aspherics.

Optimum solution for spherical primary mirror with two and three aspheric corrector plates located near focus.

Aspheric corrector plates can provide good aberration control for large spherical primary mirror telescopes, but the regions where good solutions can be obtained are very limited. Two isolated solution regions exist for the two-corrector configuration.

Aden and Marjorie Meinel's China trip October-November 1979.

The Meinels, astronomers with the Optical Sciences Center of the University of Arizona, briefly review their trip to China-both Mainland and Taiwan-and discuss the impressions gained during their few weeks there in the fall of 1979.

Minimum-cost 4-m telescope developed at October 1979 Nanjing study of telescope design and construction.

A lightweight 4-m telescope with a 6400-kg primary mirror of f/11.5 was developed during a two-week workshop at the Nanjing Astronomical Instruments Factory sponsored by the Purple Mountain Observatory, Academia Sinica, Nanjing, People's Republic of China. A central column supports the secondary mirror, thus eliminating all structures around the periphery of the primary mirror. The altazimuth mounting has the elevation axis behind the primary mirror and cell, requiring a counterweight. The Cassegrain focal position coincides with the elevation axis. A single secondary mirror and appropriate field correctors enable operations at the Harland Epps-Dan Schulte (HEDS), Cassegrain, Nasmyth, and coudé foci. Relay of the Cassegrain beam to the coudé is via an elliptical relay mirror. Cost scaling law considerations indicate that this 4-m design will have a cost comparable with that of a conventional 2.2-m telescope. A discussion of the double-tapered lightweight Cer-Vit-type mirror is included.