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Schmidt shows the application of an aspheric surface as well as an obstruction in the setup of a wide-field telescope. A Schmidt camera consists of a spherical mirror with an aspheric corrector plate at or near the center of curvature of the mirror. The purpose of the aspheric plate is to correct the spherical aberration of the mirror. In the design included here, an additional lens is placed near the image plane to correct field aberrations on a flat image plane (a normal Schmidt camera has a curved image surface). The system data is shown below.

*LENS DATA Schmidt System 100mm f/1.25 3deg SRF      RADIUS      THICKNESS   APERTURE RADIUS       GLASS SPE   NOTE

0        —        1.0000e+20    5.2408e+18             AIR 1    2.6134e+03      6.500000     42.000000         FSILICA   * 2        —         88.660000     42.000000 AP          AIR 3        —         98.860000     42.000000 X           AIR   *
4   -201.029000    -96.860000 P   55.000000      REFL_HATCH 5    -40.500000     -2.000000      7.000000         FSILICA P 6    234.033000     -0.416671      7.000000 P           AIR P 7        —            —          5.300000


SRF        CC          AD          AE          AF          AG 1      -1.000000 -5.8678e-08 -4.2209e-12  1.2779e-15 -3.0697e-19 *PICKUPS 2     AP     1 4     THM    3        2.000000 5     GLA    1 6     GLA    3      AP     5


0     SPC   5.2408e+18 1     SPC    42.000000 2     PKP    42.000000 3     SPC    42.000000 Special Aperture Group 0: A  ATP      Ellipse  AAC     Obstruct  AAN       — AX1    -7.000000  AX2     7.000000  AY1    -7.000000  AY2     7.000000
4     SPC    55.000000 5     SPC     7.000000 6     PKP     7.000000 7     SPC     5.300000

Note that an obstruction must be placed on surface 3 to block the rays that hit the image surface before hitting the primary mirror. The obstruction is specified as a special aperture as shown, and is marked not drawable, so that it does not appear in the lens drawing. The performance of the system is indicated in the ray analysis below. Note that the ray-intercept curves are not smooth. This is characteristic of designs that use high-order aspherics, as this one does. It is likely that the curves could be smoothed out by careful weighting of the variables during optimization.