# Physics - Valencia

COLLEGE PHYSICS COLLEGE PHYSICS Chapter # Chapter Title Chapter 26 VISION AND OPTICAL

INSTRUMENTS PowerPoint Image Slideshow FIGURE 26.1 A scientist examines minute details on the surface of a disk drive at a magnification of 100,000 times. The image was produced using an electron microscope. (credit: Robert Scoble)

FIGURE 26.2 The cornea and lens of an eye act together to form a real image on the light-sensing retina, which has its densest concentration of receptors in the fovea and a blind spot over the optic nerve. The power of the lens of an eye is adjustable to provide an image on the retina for varying object distances. Layers of tissues with varying indices of refraction in the lens are shown here. However, they have been omitted from other pictures for clarity. FIGURE 26.3

An image is formed on the retina with light rays converging most at the cornea and upon entering and exiting the lens. Rays from the top and bottom of the object are traced and produce an inverted real image on the retina. The distance to the object is drawn smaller than scale. FIGURE 26.4 Relaxed and accommodated vision for distant and close objects.

(a) Light rays from the same point on a distant object must be nearly parallel while entering the eye and more easily converge to produce an image on the retina. (b) Light rays from a nearby object can diverge more and still enter the eye. A more powerful lens is needed to converge them on the retina than if

they were parallel. FIGURE 26.5 (a) The nearsighted (myopic) eye converges rays from a distant object in front of the retina; thus, they are diverging when they strike the retina, producing a blurry image. This can be caused by the lens of the eye being too powerful or the length of the eye being too great.

(b) The farsighted (hyperopic) eye is unable to converge the rays from a close object by the time they strike the retina, producing blurry close vision. This can be caused by insufficient power in the lens or by the eye being too short. FIGURE 26.6

Correction of nearsightedness requires a diverging lens that compensates for the overconvergence by the eye. The diverging lens produces an image closer to the eye than the object, so that the nearsighted person can see it clearly. FIGURE 26.7 Correction of farsightedness uses a converging lens that compensates for the under convergence by the eye. The converging lens produces an image

farther from the eye than the object, so that the farsighted person can see it clearly. FIGURE 26.8 This chart can detect astigmatism, unevenness in the focus of the eye. Check each of your eyes separately by looking at the center cross (without spectacles if you wear them). If lines along some axes appear darker or clearer than others, you have an

astigmatism. FIGURE 26.9 Laser vision correction is being performed using the LASIK procedure. Reshaping of the cornea by laser ablation is based on a careful assessment of the patients vision and is computer controlled. The upper corneal

layer is temporarily peeled back and minimally disturbed in LASIK, providing for more rapid and less painful healing of the less sensitive tissues below. (credit: U.S. Navy photo by Mass Communication Specialist 1st Class Brien Aho) FIGURE 26.10

The image shows the relative sensitivity of the three types of cones, which are named according to wavelengths of greatest sensitivity. Rods are about 1000 times more sensitive, and their curve peaks at about 500 nm. Evidence for the three types of cones comes from direct measurements in animal and human eyes and testing of color blind people. FIGURE 26.11

Absorption characteristics determine the true color of an object. Here, three objects are illuminated by white light, and one by pure red light. White is the equal mixture of all visible wavelengths; black is the absence of light. FIGURE 26.12 Emission spectra for various light sources are shown. Curve A is average sunlight at Earths surface, curve B is light from a fluorescent lamp, and curve C is the output of an incandescent light. The spike for a helium-neon laser (curve D) is due to its pure wavelength emission. The

spikes in the fluorescent output are due to atomic spectraa topic that will be explored later. FIGURE 26.13 The importance of edges is shown. Although the grey strips are uniformly shaded, as indicated by the graph immediately below them, they do not appear uniform at all. Instead, they are perceived darker on the dark side and

lighter on the light side of the edge, as shown in the bottom graph. This is due to nerve impulse processing in the eye. FIGURE 26.15 Multiple lenses and mirrors are used in this microscope. (credit: U.S. Navy photo by Tom Watanabe)

FIGURE 26.16 A compound microscope composed of two lenses, an objective and an eyepiece. The objective forms a case 1 image that is larger than the object. This first image is the object for the eyepiece. The eyepiece forms a case 2 final image that is further magnified. FIGURE 26.17

(a) The numerical aperture (NA) of a microscope objective lens refers to the lightgathering ability of the lens and is calculated using half the angle of acceptance . (b) Here, is half the acceptance angle for light rays from a specimen entering a camera lens, and D is the diameter of the aperture that controls the light entering the lens. FIGURE 26.18 Light rays enter an optical fiber. The numerical aperture of the optical fiber can be determined by using the angle max.

FIGURE 26.19 Light rays from a specimen entering the objective. Paths for immersion medium of air (a), water (b) (n = 1.33) , and oil (c) (n = 1.51) are shown. The water and oil immersions allow more rays to enter the objective, increasing the resolution. FIGURE 26.20 Illumination of a specimen in a microscope.

(a) Transmitted light from a condenser lens. (b) Transmitted light from a mirror condenser. (c)

Dark field illumination by scattering (the illuminating beam misses the objective lens). (d) High magnification illumination with reflected light normally laser light. FIGURE 26.21

An electron microscope has the capability to image individual atoms on a material. The microscope uses vacuum technology, sophisticated detectors and state of the art image processing software. (credit: Dave Pape) FIGURE 26.22 The image shows a sequence of events that takes place during meiosis. (credit: PatrciaR, Wikimedia Commons; National Center for Biotechnology Information)

FIGURE 26.23 (a) Galileo made telescopes with a convex objective and a concave eyepiece. These produce an upright image and are used in spyglasses. (b) Most simple telescopes have two convex lenses. The objective forms a case 1 image that is the object for the eyepiece. The eyepiece forms a case 2 final image that is magnified. FIGURE 26.24

This arrangement of three lenses in a telescope produces an upright final image. The first two lenses are far enough apart that the second lens inverts the image of the first one more time. The third lens acts as a magnifier and keeps the image upright and in a location that is easy to view. FIGURE 26.25 A two-element telescope composed of a mirror as the objective and a lens for the eyepiece

is shown. This telescope forms an image in the same manner as the two-convex-lens telescope already discussed, but it does not suffer from chromatic aberrations. Such telescopes can gather more light, since larger mirrors than lenses can be constructed. FIGURE 26.26 (a) The Australia Telescope Compact Array at Narrabri (500 km NW of Sydney). (credit: Ian Bailey) (b) The focusing of x rays on the

Chandra Observatory, a satellite orbiting earth. X rays ricochet off 4 pairs of mirrors forming a barrelled pathway leading to the focus point. (credit: NASA) FIGURE 26.27 An artists impression of the Australian Square Kilometre Array Pathfinder in Western

Australia is displayed. (credit: SPDO, XILOSTUDIOS) FIGURE 26.28 (a) Chromatic aberration is caused by the dependence of a lenss index of refraction on color (wavelength). The lens is more powerful for violet (V) than for red (R), producing images with different locations and

magnifications. (b) Multiple-lens systems can partially correct chromatic aberrations, but they may require lenses of different materials and add to the expense of optical systems such as cameras. FIGURE 26.29

A coma is an aberration caused by an object that is off-center, often resulting in a pearshaped image. The rays originate from points that are not on the optical axis and they do not converge at one common focal point. FIGURE 26.30 Spherical aberration is caused by rays focusing at different distances from the lens. This OpenStax ancillary resource is Rice University under a CC-BY 4.0 International license; it may be reproduced or modified but must

be attributed to OpenStax, Rice University and any changes must be noted.

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