1. THIN LENSES

2. Thin lenses Convex Converging f > 0 f Concave Diverging f < 0

3. First and second focal points of a converging thin lens
First and second focal points of a converging thin lens. The numerical value of f is positive.

4. Construction used to find the image position for a thin lens.

5. Three easy rays for ray-tracing
Objects and images S S’ x y f f
Three easy rays for ray-tracing
Thin lens equation
magnification

6. S’, f and S are all positive
Reading the signs
In this diagram
The object is “upstream” of the lens.
The lens is a converging lens.
The image is a real image through which light rays actually pass, and it is “downstream” of the lens.
S’, f and S are all positive

7. Formation of images by a thin converging lens for various object distances.

8. Two types of images Real image
i > 0 , so light rays pass through image point (“in front” of mirror)
Inverted
Virtual image
i < 0 , so light rays do not pass through image point (“behind” mirror)
Upright

9. First and second focal points of a diverging thin lens
First and second focal points of a diverging thin lens. The numerical value of f is negative.

10. A negative lens Upright, virtual image 37.5% as large as object
S = +50 cm
f = -30 cm
S’ = cm
m =
Upright, virtual image
37.5% as large as object

11. Principal-ray diagram for an image formed by a thin diverging lens.

12. Optical Instruments

13. A typical single lens reflex camera
A typical single lens reflex camera. The lens has many elements cemented together to form a single compound lens.

14. The larger image size with a larger value of f corresponds to a smaller angle of view.

15. In a camera lens, larger f-numbers mean smaller aperture diameters.
f-number = f / D where D = diameter of aperture

16. Overhead projector. The inexpensive plastic Fresnel lens is like an ordinary thick lens with the internal material removed.

17. The eye. The muscle contracts to change the focal length of the lens to image close objects.

18. Refractive errors for a myopic (nearsighted) eye and a hyperopic (farsighted) eye viewing a very distant object. The dashed blue curve indicates the correct position of the retina.

19. (a) An uncorrected hyperopic (farsighted) eye
(a) An uncorrected hyperopic (farsighted) eye. (b) A positive (converging) lens gives the extra convergence needed for a hyperopic eye to focus the image on the retina. The virtual image formed by the converging lens acts as an object at the near point.

20. Microscope Basics Originally conformed to the German DIN standard
Standard required the following
real image formed at a tube length of 160mm
the parfocal distance set to 45 mm
object to image distance set to 195 mm
Currently we use the ISO standard
Object to
Image
Distance
= 195 mm
Mechanical
tube length
= 160 mm
Focal length
of objective
= 45 mm

21. The Conventional Microscope
Mechanical
tube length
= 160 mm
Object to
Image
Distance
= 195 mm
Focal length
of objective
= 45 mm

22. The image produced by first lens acts as a virtual object for the second lens.