Warm Up A concave mirror has a focal length of 5 cm. If an object is 2 cm away from the mirror, where is the image? A convex mirror has a focal length of 10 cm. A person looks at their eyeball in the mirror 8 cm away. Where is the image?

Optics: Reflection, Refraction Lenses 05/25/2006 Optics: Lenses Lecture 16

Analogy… Mirrors make images with reflection Lenses make images with refraction!

Remember…. Virtual images are located where reflected light appears to converge Real images are located where reflected light actually converges

Convex Lenses Thicker in the center than edges. Two focii (one on either side) Lens that converges (brings together) light rays. Light traveling is refracted through lens, then refracted again back into air Any ray traveling parallel Will be refracted through focal point

Convex Lenses Lens that converges (brings together) light rays. Forms real images and virtual images depending on position of the object The Magnifier

Lens Ray Diagram Rules Three Rays: Ray goes parallel, refracted through f (on other side) Ray goes through f (on same side), gets refracted parallel (on other side) Ray goes through the center of lens

Concave Lenses Lenses that are thicker at the edges and thinner in the center. Diverges light rays All images are right side up and reduced. The De-Magnifier

How You See Near Sighted – Eyeball is too long and image focuses in front of the retina Near Sightedness – Concave lenses expand focal length Far Sighted – Eyeball is too short so image is focused behind the retina. Far Sightedness – Convex lens shortens the focal length.

Optics: Reflection, Refraction 05/25/2006 Cameras, in brief pinhole image at film plane object In a pinhole camera, the hole is so small that light hitting any particular point on the film plane must have come from a particular direction outside the camera image at film plane object lens In a camera with a lens, the same applies: that a point on the film plane more-or-less corresponds to a direction outside the camera. Lenses have the important advantage of collecting more light than the pinhole admits Lecture 16