Principle

The focal lengths of unknown lenses are determined by measuring the distances of image and object and by Bessel's method. Simple optical instruments are then constructed with these lenses.

Tasks

1. To determine the focal length of two unknown convex lenses by measuring the distances of image and object.
2. To determine the focal length of a convex lens and of a combination of a convex and a concave lens using Bessel's method.
3. To construct the following optical instruments:
   a) Slide projector; image scale to be determined
   b) Microscope; magnification to be determined
   c) Kepler-type telescope
   d) Galileo's telescope (opera glasses).

Learning objectives

• Law of lenses
• Magnification
• Focal length
• Object distance
• Telescope
• Microscope
• Path of a ray
• Convex lens
• Concave lens
• Real image
• Virtual image

Benefits

• Understand a basic optical component: the lens
• Learn how common optical instruments work
• Geometric optics in a nutshell