| 摘要 |
<p>PURPOSE: To provide an optical device which has aberrations improved furthermore by rotating a compensation plate around a beam axis at a prescribed angle to an optical element to completely eliminate the astigmatism due to the optical element. CONSTITUTION: A filter or an element 1 like a plate is arranged on an optical axis 0-0. For the purpose of compensating the astigmatism of the optical image formed through the plate (platy element) arranged at an angle, a compensation plate 2 is provided on the optical axis 0-0 and is so arranged that it is rotated at 90 deg. to the direction of the plate 1. Aberrations which have the same magnitude as the filter or the plate 1 and are rotated at 90 deg. to them are introduced by this compensation plate 2. The power in the vertical direction is reduced as the result of the astigmatism due to the first plate 1, and the power in the horizontal direction orthogonal to the optical axis 0-0 is reduced by the compensation plate 2. The power is symmetrically reduced in the pupil position by combination of them to introduce negative defocusing, and as a result, the astigmatism becomes zero and is shifted to the image forming position.</p> |
