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TM 9-254
9-2.
Optical Components - Continued
(4)
Penta Prism. A Penta prism, as shown in figure 9-13, is a five sided prism with two silvered surfaces. It
is used to bend light rays through a constant angle, usually 90 degrees, without producing inversion or
reversion if reflection takes place in the vertical or horizontal plane.
Figure 9-13. Penta Prism
(5)
Pechan Prism. A Pechan prism, as shown in figure 9-14, is a rotating pechan or Z prism consisting of
two prisms separated at an angle to 45 degrees with two external reflecting surfaces that are silvered.
This type of prism is used to invert the image in one plane without deviating or displacing the axis of the
light rays. It is used in the conventional types of optical systems in panoramic telescopes.
Figure 9-14. Pechan Prism
Change 2 9-9
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