| 摘要 |
This invention provides, in a restricted off-axis field optical system having a broad spectral range, which includes refracting elements, the improvement comprising: an optical system constructed and arranged so that the Petzval sum is substantially zero, said refracting elements including elements for balancing the effects of the variation in the Petzval sum due to variation in color by introducing axial chromatic aberration of the opposite sense so that the position of focus at the off-axis field remains substantially constant; according to the invention in one form thereof, the elements for balancing the effects of the variation in the Petzval sum due to variation in color include a symmetrically disposed nearly concentric meniscus element whose convex radius is larger than its concave radius and whose thickness is greater than the difference between its convex and concave radii; further, according to a form of the invention, the system includes at least one convex and one concave mirror, said mirrors being nearly concentrically arranged along an optical axis; further, according to one form thereof, the system includes a color trimming element; the invention according to a form thereof, includes an optical system having a first half and a second half, each half including an optical system having an optical axis and having conjugate planes substantially normal to that axis, the first half and the second half being coaxially disposed in back-to-back relationship so that the conjugate planes are superimposed on at least one side of the optical system, and provision is made for spacing the object and final image locations on the other side of the optical system.
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