1. Lenses Properties, Characteristics & Ray Diagrams

2. Properties & Characteristics Lens = any transparent object with two refractive sides whose index of refraction is greater than air. Types of Lenses: 1. Convex Lens – ◦ Thicker at center ◦ Converging lens (refract parallel light rays so they meet) ◦ Sets ants on fire!!!

3. Properties & Characteristics (cont.) Types of Lenses (cont.): 2. Concave Lens – ◦ Thinner at center ◦ Diverging lens (rays spread out)

4. Properties & Characteristics (cont.) Large Lenses – collect more light, makes image brighter and clearer Spherical aberration – the inability to focus all light rays to a single point. (fuzzy image) Chromatic aberration – dispersion of light rays near the edges. (rings of color around image) **fix = achromatic lens…combo of a concave & a convex lens**

5. Corrective Lenses Near-sighted – can’t see distant objects, image focused in front of retina. Fix = concave lens Far-sighted – can’t see close objects, image focused behind retina. Fix = convex lens Astigmatism – eye isn’t spherically shaped. Fix = nonspherical lens

6. Lens Ray Diagrams Focal point still = “F” (on both sides) Focal length (f)= distance from lens to focal point There is no “C” New Stuff: 2F = twice the distance of F (on both sides) Principle plane (optical plane) = vertical line through middle of lens; perpendicular to principle axis

7. Lens Ray Diagrams (cont.) New Stuff (cont.): If image is on the same side of lens as object = virtual If image is on opposite side of lens as object = real

8. Convex Lens Diagram Find “F” and “2F” on each side of the lens. Draw in the principle plane Ray #1 – from top of object parallel to principle axis, hits principle plane and refracts through “F” on the other side of lens. Ray #2 – from top of object through “F” on same side of lens, hits principle plane and refracts parallel to principle axis. The intersection of the two rays = location of image. Describe the image – bigger/smaller; upside down/right side up; real/virtual. **Remember refracted rays can always be extended in either direction**

9. Concave Lens Diagram Find “F” and “2F” on each side of the lens. Draw in the principle plane. Use 2 rays to locate image. Ray #1 – from top of object parallel to principle axis, hits principle plane and refracts as if it is traveling from “F” (on same side as image), it also reflects through “F” on the same side as the object. Ray #2 – from top of object through the center of the lens (where principle plane and principle axis meet) without bending. The intersection of the two rays = location of image. Describe the image – bigger/smaller; upside down/right side up; real/virtual.