8. Zoom Lenses and Afocals

8.1. Zoom Lenses

• https://www.premiumbeat.com/blog/how-to-use-zoom-lenses/

• https://en.wikipedia.org/wiki/Zoom_lens

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)$$\frac{{\theta }_2}{{\theta }_1}=\frac{f_1}{f_2}$$