1. Lenses

2. Lenses
Although a flat piece of glass refracts light, it only displaces the light laterally. The rays remain parallel.

3. Lenses
Lenses are transparent objects with at least one curved side that refract light.
Although size and profile of lenses may vary, there are 2 basic shapes

4. TYPES OF LENSES
CONVERGING OR CONVEX
DIVERGING OR CONCAVE

5. Generally, light traveling through lenses is bent twice: once when it enters the lens and once when it leaves.
In the case of a thin lens, it is possible to neglect this double bending.
positive side of a lens
negative side of a lens
Light travels from the negative side of a lens to the positive side of a lens.

6. Converging Lens f f F’ F Principal Axis
All light rays travelling parallel to the principal axis will refract through the focal point of a converging lens.
The distance from the lens to this point is called the focal length of the lens, f.
Lenses have two focal points, one on each side, at equal distances from the lens. The lens does not have to have the same curvature on both sides for this to be true.

7. Converging Lens 2F’ F’ 2F F
Rule #1 All incident light rays travelling parallel to the principal axis will refract through the focal point (F) of a converging lens.

8. Converging Lens 2F’ F’ 2F F
Rule #2 All incident light rays passing through the optical centre of the lens (the vertex) will be refracted and undeviated.

9. Converging Lens 2F’ F’ 2F F
Rule #3 All incident light rays passing through the focal point (F’) will be refracted parallel to the principal axis.

10. Converging Lens 2F’ F’ 2F F Object distance is beyond 2F’
image
2F’ F’ 2F F
Object distance is beyond 2F’
The image is:
Smaller, Inverted, Between 2F and F, Real

11. Converging Lens 2F’ F’ 2F F Object distance is at 2F’ The image is:
Same size, Inverted, At 2F, Real

12. Converging Lens 2F’ F’ 2F F Object distance is between 2F’ and F’
image
Object distance is between 2F’ and F’
The image is:
Larger, Inverted, Beyond 2F, Real

13. Converging Lens 2F’ F’ 2F F Object distance is at F’
No clear image is visible

14. Converging Lens 2F’ F’ F 2F
image
2F’ F’ F 2F
object
Object distance is inside F’ (between F’ and the optical center of the lens)
The image is:
Larger, Upright, Same side as object (behind lens), Virtual

15. Diverging Lens f F’
Any incident light ray travelling parallel to the principal axis will diverge from the focal point (F) of a diverging lens after refraction.
The focal length is the distance from the lens to the focus
A concave lens has a VIRTUAL focal point.

16. Diverging Lens F’
Rule #1 Any incident light ray travelling parallel to the principal axis is refracted as if it had come through the principal focus.

17. Diverging Lens F’ F
Rule #2 Any incident light ray that appears to pass through the secondary principal focus (F’) is refracted parallel to the principal axis.

18. Diverging Lens F’ F
Rule #3 A incident ray through the optical center (O) continues straight through on its path.

19. Note: No matter where the object is placed, the image is alwaysF
object
image
Note: No matter where the object is placed, the image is always
SMALLER, UPRIGHT, CLOSER, VIRTUAL