# Chapter 35: Lenses

A lens is essentially a medium with a different index of refraction than the surrounding medium. The shape and index of refraction of the lens determine its properties. The key to designing optical systems is understanding the image formed by a given lens or combination of lenses. In this chapter many of the concepts of image formation are similar to those for spherical mirrors. The problems you will encounter will use ray diagrams to explore image formation, determine focal points, and develop methods for understanding multiple-lens systems.

# Table of Contents

# Illustrations

- Illustration 35.1: Lenses and the Thin-Lens Approximation.
- Illustration 35.2: Image from a Diverging Lens.

# Explorations

- Exploration 35.1: Image Formation.
- Exploration 35.2: Ray Diagrams.
- Exploration 35.3: Moving a Lens.
- Exploration 35.4: What is Behind the Curtain?
- Exploration 35.5: Lens Maker's Equation.

# Problems

- Problem 35.1: Hidden lenses, point sources.
- Problem 35.2: Hidden lenses, mixed sources.
- Problem 35.3: Hidden lenses, point sources.
- Problem 35.4: Focal length of converging lens.
- Problem 35.5: Focal length of lens system.
- Problem 35.6: Image location, beam source.
- Problem 35.7: Image location, point source.
- Problem 35.8: Find the focal length of each lens in the 2-lens system.
- Problem 35.9: Find the focal length of each lens in the 2-lens system.
- Problem 35.10: Find the focal length of each lens in the 3-lens system.
- Problem 35.11: Build a converging lens.