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. 2016 Apr 25;93(5):521–533. doi: 10.1097/OPX.0000000000000820

FIGURE 8.

FIGURE 8

(A) The calculated (solid line) and measured (solid squares) deflection angles, at normal incidence, of a bi-part prism constructed from two PMMA Fresnel prisms of 36Δ as a function of angle, &thetas;, between them. The nominal deflection angle (normal incidence) for a bi-part prism converges to a fixed value of about 38 degrees (∼78Δ) for angles between the prisms larger than 29 degrees. As the angle between the prisms is reduced, the deflection angle increases rapidly and the transmittance also decreases rapidly toward the critical angle (angle of TIR). Rated prism powers of conventional 57Δ (dotted line) and 36Δ (dashed line) are illustrated. (B) The tilt angle for the oblique design (with 12-mm interprism separation) needed to close the gap (33 degrees) between the expansion areas as a function of the angle between the bi-part prisms. The tilt angle required to close the gap with conventional 57Δ (dotted line) and 36Δ (dashed line) are illustrated for comparison.