8. Zoom Lenses and Afocals#

8.1. Zoom Lenses#

8.2. Afocals (Beam Expander)#

Afocals are so called because neither the input nor the output comes to an image.

A ray diagram for an afocal lens.

Beam expansion:

(8.1)#\[ \tan (\theta_3) = \frac{h_2}{f_1} \approx \theta_3 \]
(8.2)#\[ \tan (\theta_3) = \frac{h_3}{f_2} \approx \theta_3 \]
(8.3)#\[ \frac{h_3}{h_2} = \frac{f_2}{f_1} \]

Angle:

(8.4)#\[ \frac{h_1}{f_1} = \theta_1 \]
(8.5)#\[ \theta_2 = \frac{h_1}{f_2} \]
(8.6)#\[ \frac{\theta_2}{\theta_1} = \frac{f_1}{f_2} \]