Converging and Diverging Lenses

1. Converging and Diverging Lenses • Lenses are used to focus light and form images. • There are a variety of possible types • We will consider only the symmetric ones • the double concave and the double convex.

2. Convergingat the Focal Point • For a double convex (i.e. converging) lens, the light refracts such that it converges at the focal point.

3. Diverging from the Focal Point • A double concave (i.e. diverging) lens has the refracted rays diverging as if they all come from the focal point.

4. Constructing Ray Diagrams Draw two of the three principal raysoriginating from the same point on the object and follow these rules: 1. P-Ray is drawn through a point on the object and parallel to the principal axis. It is refracted through the focal point, F. 2.F-Rayis drawn through a point on the object and through (convex) or towards (concave) the focal point. it is refracted parallel to the principal axis. 3.V-Rayis drawn through a point on the object and through the vertex. It goes straight through and does NOT change direction (assuming lens is thin) 4

5. Rays – Converging Lens

6. Image Types – Converging Lens Converging = Convex The convex lens forms different image types depending on where the object is located with respect to the focal point 5 possible object locations • Case 1: The object is located in front of F • Case 2: The object is located at 2F • Case 3: The object is located beyond 2F • Case 4: The object is located between F and 2F • Case 5: The object is located at F, the focal point. Please complete handout for CONVEX lenses (front half) (two examples are done for you on the next slides to help get you started)

7. Image Types – Converging Lens Case #1: Object is Located in front of F Notice that you refract the ray along the optic axis  i.e. the middle of the lens

8. Image Properties – in front of F L – O – S – T - Same side of lens as object Upright Larger Virtual Notice here that for location, you are telling me what SIDE of the lens the image is on (same side or opposite side as the object)

9. Ray Diagram - Converging Lens Case #2: Object is Located at 2F

10. Image Properties – at 2F L – O – S – T - At 2F – Opposite Side Inverted Equal Real Notice here that for location, you are giving an approximate location (between __ and ___, or at ____), but you are also telling me what SIDE of the lens the image is on (same side or opposite side as the object)

11. Rays – Diverging Lens Diverging = CONCAVE

12. Ray Diagram - Diverging Lens Locate the image of an object located between F and 2F for a diverging lens

13. Diverging Lenses • Complete the ray diagrams for concave/diverging lenses • You only need to complete two or three of these … if you catch on to the trend, you can stop!

14. Complete the summary table for Image properties of Diverging and Converging (next slide)

15. Summary: Image Characteristics formed by Concave and Convex Lenses