1. 2 types of lenses just like mirrors
Lens Ray Diagrams
2 types of lenses just like mirrors
Convex Lens - Converging - thick in middle, thin edge - Opposite of mirror
Concave Lens - Diverging - thin in middle, thick edge

2. General Information for all lenses
The principle axis still exists line parallel to center of lens
The focal point is no longer 1/2 distance from CC
The focal point depends on both curvature and the way the lens refracts light
There are 2 focal points. f1 and f2- one on each side of lens
The ray method for lenses is similar to mirrors.

3. Ray Diagrams: Convex Lens
Ray #1: Light travels parallel & refracts through focal point f2
Ray #2: Light travels straight through the center of the lens
Ray #3: Light travels through first focal point(f1) & refracts parallel to the principle axis

4. Object at infinity - image located at f2
Object at infinity - image located at f2. This is one way to find the focal point 2f f f 2f 1 1 2 2

5. Object located beyond 2f1 - image is located between f2 and 2f2 …Image real, inverted, smaller

6. Sample problem
A 3 cm object is located 12 cm from a convex lens with a focal length of 3 cm. Where would the image be located? What is the size of the image?

7. Image Location Given: So=3 cm do=12 cm f=3 cm 1/di + 1/do = 1/f
1/di = (1/f)-(1/do)
1/di = (1/3) - (1/12)
1/di = 4/12 - 1/12 = 3/12
di = 12/3 = 4 cm

8. What is the size of the image?
si/so = -di/do
si = -so di /do
- 4cm (3cm) /12 cm = -1 cm

9. Object located @ 2f1 - image is located at 2f2 …Image real, inverted, same size

10. Object located between 2f1 & f1 - image is beyond 2f2 … Image real, larger, inverted

11. Object located at f1 Rays refracted parallel - No Image2 2

12. Object located closer than f1 … Trace diverging rays backwards Image is erect, larger and virtual2 2

13. Ray Diagrams: Concave (Diverging) Lens
1st Ray: Parallel to the Principle axis, as if it had come from the 1st focal point (f1)
2nd Ray: Straight through the center of the lens
3rd Ray: Heads toward 2nd focal point (f2) & refracts parallel

14. Object at infinity - image located at f1 and is virtual2 2

15. Object located @ 2f1 ……Image is virtual, upright, smaller

16. Object located between 2f1 and f1 ……Image is virtual, upright, smaller

17. Object located @ f1 ……Image is virtual, upright, smaller2 2

18. Concave (Diverging) Lens
Always form images that are
Virtual
Upright
Smaller