Question

1. A Galilean beam expander is really a Galilean telescope used in reverse (see notes page 2-33a). A rallel beam of light enters a negative lens, diverges and enters a longer focal length positive lens of r diameter. The focal points of the two lenses are coincident on the input side of the instrument and the separation d = f, + , between the two thin lenses (center to center) is 90 cm. Assume fi 12.0 cm and f,:+21.0 cm, make a scaled ray diagram of the beam expander. From both algebra and your ray trace, find the lateral magnification of the instrument, which should agree with the formula given in the class notes

Answer 1

The ray diagram is given in the figure below:

2

Lateral magnification of the instrument is:

|m| = f₂/f₁ = 21/12 = 1.75