2 Introduction We will discuss: Cameras The eye The simple magnifier The compound microscopeThe telescopeThe Michelson interferometerThe diffraction grating
3 The Camera A single lens camera consists of: A light tight box A converging lensProduces a real, inverted imageFocusing is done by adjusting the distance between the lens and the film.A shutter25.1
4 Camera Variables Shutter speeds Aperture size Control exposure times Faster shutter speeds for faster objects or for bright lightAperture sizeLarger 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 lensA measure of the light concentrating power of the lensA small f-number means that the aperture is wide open
11 The cornea does over 70 % of the refracting. The lens makes the final adjustment.
12 The Near PointThe 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 10About 25 cm at age 20About 50 cm at age 40500 cm or greater at age 60
13 The Far PointThe 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 lensMyopia (nearsightedness)Corrected with a diverging lensAstigmatismCorrected by using cylindrical lenses25.3, 25.4, 30-1
16 Diseases of the EyeCataractsThe lens is surgically replaced
17 GlaucomaCorrected by medication or YAG solid state laser surgery
18 The Power (P) of a Lens Measured in diopters (no abbreviation) Used in lens prescriptionsFormula:f must be in meters
19 The Simple Magnifier Consists of a single converging lens Increases the apparent size of an object25.6a, 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 magnifierAn objective with a short focal length ( )An eyepiece (ocular) with a focal length( ) of a few centimetersLenses are separated by a distance (L) which is greater than either or25.7a
24 Microscope ImagesThe image formed by the objective becomes the object for the eyepiece.The image is inverted with respect to the object.
39 ImagesMicroscopes 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 light25.10
41 Maximum ResolutionIf 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 CriterionWhen 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)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.