Lens Basics Depiction of Archimedes burning glass Made

Lens Basics

• Depiction of Archimedes’ burning glass.

Made With Precision • A lens is merely a carefully ground piece of transparent material which refracts light rays in such a way as to form an image.

Types of Lenses • There are two types of lenses. Convex Lens Concave Lens (Converging) (Diverging) Thicker in the middle than at the ends Thinner in the middle than at the ends

Anatomy of a Lens Optical Axis Lens Focal Points Optical Center Principal Axis

Image Formation in Lenses

$Refraction is Key • The examples below illustrate how lenses can distort light. Convex$

Refraction is Key • The examples below illustrate how lenses can distort light. Convex Converging Lens Concave Diverging Lens

What Do You See? • Objects will also be distorted when viewed through a lens. Convex Concave

Ray Diagrams • We can use ray diagrams to predict how an image will look through a lens.

$Rules for Convex Ray Diagrams Incident Ray Refracted Ray Diagram 1 Parallel to principal$

Rules for Convex Ray Diagrams Incident Ray Refracted Ray Diagram 1 Parallel to principal axis Through second focal point 2 Through optic center Ray stays along the same path F 1 F 2 3 Through first focal point Parallel to principal axis F 1 F 2

Completed Diagram • Consider the following situation: Notice that if you looked at this candle through this convex lens, the candle would appear smaller and inverted! We will describe images in more detail later.

Try This!

Real and Virtual Images • A real image can be projected on a screen • A virtual image can be seen but cannot be projected on a screen. Living Graphs – Looking Glass Program

Completed Diagram • Consider the following situation: F 1 F 2 Notice that if you looked at this candle through this concave lens, the candle would appear smaller.

Describing Images • We describe how an image looks by explaining how each of the four variables below change. Image Characteristics Description S Size (or Magnification) Enlarged or Diminished A Attitude Upright or Inverted L Location Object side or Opposite side of lens T Type Real or Virtual

What is a Virtual Image? • A virtual image is an optical illusion. • You can see an image, but no light is actually there. It simply appears to be there! Real Image Formed Virtual Image Formed

Example 1

Example 2

Example 3

Example 4

• The following slides can be photocopied on to one legal sheet for student reference.

SALT – Image Description Image Characteristics Description S Size (or Magnification) Enlarged or Diminished A Attitude Upright or Inverted L Location Object side or Opposite side of lens T Type Real or Virtual

$Rules for Convex Ray Diagrams Incident Ray Refracted Ray Diagram 1 Parallel to principal$

Rules for Convex Ray Diagrams Incident Ray Refracted Ray Diagram 1 Parallel to principal axis Through second focal point 2 Through optic center Ray stays along the same path F 1 F 2 3 Through first focal point Parallel to principal axis F 1 F 2

$Rules for Concave Ray Diagrams Incident Ray Refracted Ray Diagram 1 Parallel to principal$

Rules for Concave Ray Diagrams Incident Ray Refracted Ray Diagram 1 Parallel to principal axis As if it came from the first focal point 2 Through optic center Ray stays along the same path F 1 F 2 3 Toward the second focal point Parallel to principal axis F 1 F 2