| 摘要 |
The present invention selectively corrects astigmatism and is simple and inexpensive to implement. A spherical mirror is bent to simultaneously increase radius of curvature in one plane and decrease radius of curvature in the plane at right angles thereto. In one implementation the mirror disposed in a mounting that includes a plurality of abutment surfaces against which a front surface of the spherical mirror abuts to effect bending of the mirror when it is appropriately disposed in the mounting. The plurality of abutment surfaces includes at least two bending surfaces and at least two support surfaces. The bending surfaces are higher than the support surfaces, relative to a surface of the mounting from which they extend. When the mirror is appropriately disposed in the mounting, the bending surfaces push the mirror at particular bending locations at opposite sides of the mirror in the plane of incidence, while the mirror is supported by the support surfaces at two particular support locations at right angles to the plane of incidence. Mounting the mirror in contact with each of the bending surfaces and support surfaces has the effect of flattening or subtracting a cylindrical component from the curvature of the mirror in a first plane (i.e. in the plane of incidence), while steepening or adding a cylindrical component to the curvature in a second plane (i.e. at right angles to the plane of incidence).
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