1. Optical Instruments
Chapter 25

2. Introduction We will discuss: Cameras The eye The simple magnifier
The compound microscope
The telescope
The Michelson interferometer
The diffraction grating

3. The Camera A single lens camera consists of: A light tight box
A converging lens
Produces a real, inverted image
Focusing is done by adjusting the distance between the lens and the film.
A shutter
25.1

4. Camera Variables Shutter speeds Aperture size Control exposure times
Faster shutter speeds for faster objects or for bright light
Aperture size
Larger aperture needed for low light conditions

5. f-number The ratio of the focal length to the diameter of the lens
Determines the speed of the lens
A measure of the light concentrating power of the lens
A small f-number means that the aperture is wide open

6. The equation for lateral magnification:

7. The London Eye

8. The Human Eye Parts of the eye: Cornea Aqueous humor Iris and pupil
Crystalline lens
Vitreous humor
Retina
Rods and cones
B13

9. Accommodation
Ciliary muscles
Relaxed when viewing distant objects

10. The focal length of the eye is about 1.7 cm.

11. The cornea does over 70 % of the refracting.
The lens makes the final adjustment.

12. The Near Point
The near point is the closest distance for which the lens will produce a sharp image of a nearby object on the retina.
About 18 cm at age 10
About 25 cm at age 20
About 50 cm at age 40
500 cm or greater at age 60

13. The Far Point
The far point is the farthest distance for which the lens will produce a sharp image of a far away object on the retina.
Objects located beyond the far point will be out of focus.

14. Defects of the Eye Hyperopia (farsightedness) Myopia (nearsightedness)
Corrected with a converging lens
Myopia (nearsightedness)
Corrected with a diverging lens
Astigmatism
Corrected by using cylindrical lenses
25.3, 25.4, 30-1

15. Astigmatism Test

16. Diseases of the Eye
Cataracts
The lens is surgically replaced

17. Glaucoma
Corrected by medication or YAG solid state laser surgery

18. The Power (P) of a Lens Measured in diopters (no abbreviation)
Used in lens prescriptions
Formula:
f must be in meters

19. The Simple Magnifier Consists of a single converging lens
Increases the apparent size of an object
25.6a, b

20. Angular Magnification (m)
Angular Magnification is the ratio of the angle subtended by the object when the lens is in use to the angle subtended by the object when it is placed at the near point with no lens

21. Maximum angular magnification occurs when the image formed by the lens is at the near point of the eye (more eye stress).

22. Angular magnification (m) when the image formed by the lens is at infinity (relaxed eye):

23. The Compound Microscope
Uses two lenses to achieve greater magnification than the simple magnifier
An objective with a short focal length ( )
An eyepiece (ocular) with a focal length
( ) of a few centimeters
Lenses are separated by a distance (L) which is greater than either or
25.7a

24. Microscope Images
The image formed by the objective becomes the object for the eyepiece.
The image is inverted with respect to the object.

25. Microscope Equations
Magnification equations:

26. The Electron Microscope
Atoms could never be seen with a compound microscope by using visible light
The wavelength of light is too large

27. The Telescope
There are two fundamentally different types of telescopes.

28. The Refracting Telescope

29. The Reflecting Telescope

30. The Refracting Telescope
It uses a combination of lenses.
The image (q1) formed by the first lens becomes the object (p2) for the second lens.
The image is inverted.
25.8a

31. Refracting Telescope Difficulties
Large refracting telescopes are difficult to manufacture and are expensive.
In addition, their large masses would lead to sagging which would cause distortion.

32. The Reflecting Telescope
Reflecting telescopes are preferred in astronomy.
A parabolic mirror replaces the objective.
Spherical aberration is reduced.
Chromatic aberration is
virtually eliminated.

33. The Newtonian Focus
Reflecting Telescopes use the Newtonian focus.

34. Large Telescopes
The largest telescopes in the world are reflecting telescopes.
10 meter lens in Hawaii
5 meter lens on Mt. Palomar in California

35. Canada-France-Hawaii

36. Mt. Palomar

37. The largest refracting telescope in the world is at Yerkes Observatory in Wisconsin
Only 1 meter in diameter

38. Yerkes Observatory

39. Images
Microscopes and telescopes can only form virtual images.

40. Resolution Of Single-Slit And Circular Apertures
It is important to be able to distinguish between two closely spaced objects.
This ability is limited by the diffraction of light
25.10

41. Maximum Resolution
If the two sources are separated so that their central maxima do not overlap, their images can be distinguished and they are said to be resolved.
Maximum resolution occurs at the shortest possible wavelength.
265

42. Rayleigh’s Criterion
When the central maximum of one image falls on the first minimum of another image, the images are said to be resolved.
Equations for the resolution of a circular aperture (q is in radians)
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266

43. The Diffraction Grating
Diffraction gratings are preferred over single or double slits when accurate wavelength measurements are needed.
They have a much higher resolution and provide a brighter pattern.

44. The Michelson Interferometer
It splits a light beam into two parts and then recombines them to form an interference pattern.
262

45. The Michelson Equation
L is the length of travel of the adjustable mirror.
N is the number of fringe shifts.

46. Questions
1, 3, 4, 6 - 9, 11, 13
Pg. 842