Figure 4-18. Extent of displacement of light may be change by movement of wedge

TM 9-258

f. Another means of varying the path of light is

through the use of pairs of wedges which are geared to

rotate in opposite directions. The wedges of such a

system are referred to as rotating wedges or rotating

compensating wedges. When the thicker edges of two

of these wedges are together (A, fig 4-19), they produce

a deviation twice that of one wedge and in the direction

of the thicker edges of the wedges. When rotated until

the thick edge of one wedge is toward the thin edge of

the other (B, fig 4-19), the wedges neutralize one another

and the wedges produce no deviation. Intermediate

positions cause a deviation which increases as the thick

edge of one wedge rotates farther from the thin edge of

the other. When both wedges are rotated through 180ƒ

(C, fig 4-19), the thick edges again are together and the

wedges function as in A, figure 4-19, except in the

opposite direction.

Figure 4-18. Extent of displacement of light may be

changed by movement of wedge.

4-20