Spherically corrected reflecting objective for unit magnification.
Cassegrainian-type reflecting objectives are useful as in-line imaging devices for fast spectrometer systems. They are inherently free from chromatic aberrations and may be corrected for spherical aberration. A particularly simple design, consisting of two mirrors with oppositely equal curvatures, is possible when unit magnification is desired. This system has zero third-order spherical aberration, and all other aberrations are small also. Its main disadvantage is the loss due to the central obstruction of the beam, amounting to about 28% exclusive of reflection losses. The author is with the Analytical Chemistry Division, National Bureau of Standards, Washington, D.C. 20234.
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