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Optical System Layout 327
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LASER
DIODE
ASPHERIC
COLLIMATOR WEAK
CYLINDER
LENS
LENS
Figure 13.28 The anamorphic action of refracting prisms.
axial astigmatism only when used in parallel (collimated) light. Unlike
cylindrical systems, they cannot be focused by changing the space
between elements. For this reason, prism anamorphics are frequently
preceded by a focusable pair of spherical elements which collimate the
light from the object.
For use in systems which are not monochromatic, the prisms must
be achromatized (as discussed in Sec. 7.5). Prism anamorphs have
been used to project wide-screen (anamorphosed) movies; in this appli-
cation, each achromatic prism component typically consisted of two or
three prism elements. The useful field of such a device is rather small;
being completely unsymmetric, it has all (both odd and even) orders
of aberrations, including some unusual kinds of lateral color and
distortion.
