ch30_nkct

 =Chapter 30 Review: Lenses =  aberration astigmatism converging lens cornea diverging lens eyepiece farsighted focal length focal plane focal point iris lens nearsighted objective lens principal axis pupil ray diagram real image retina virtual image 
 * Glass of a certain shape can form an image that appears larger, smaller, closer, or farther than the object being viewed.
 * Today eyeglasses allow millions of people to read in comfort, and cameras, projectors, telescopes, and microscopes widen our view of the world.
 * Important Terms You Should Know: **

 30.1 Converging and Diverging Lenses
>> >>  >> >> >> []  >> >> >> >>  http://www.glenbrook.k12.il.us/gbssci/phys/CLass/refrn/u14l5a2.gif  <span style="font-family: Georgia,serif;">
 * <span style="font-size: 90%; font-family: Georgia,serif;"><span style="font-size: 90%; font-family: Georgia,serif;"><span style="font-size: 132%; font-family: 'Times New Roman',Times,serif;">W <span style="font-size: 132%; font-family: Georgia,serif;">hen a piece of glass has just the right shape (or other transparent material), it bends parallel rays of light so that they cross, or appear to cross, and form an image at a single point. This is called a <span style="font-size: 110%; font-family: Georgia,serif;">**<span style="font-size: 120%; color: rgb(29, 10, 169); font-family: 'Times New Roman',Times,serif;">lens **.
 * <span style="font-size: 95%; font-family: Georgia,serif;">lenses manipulate light; they may be thought of as a set of prisms that when arranged in certain positions, the prisms bend incoming parallel rays so they converge to (or diverge from) a single point.
 * <span style="font-size: 90%; font-family: Georgia,serif;"><span style="font-family: Georgia,serif;">H <span style="font-size: 120%; font-family: Georgia,serif;">ere is an example of the two types of lenses: <span style="font-size: 144%; color: rgb(8, 16, 191); font-family: Georgia,serif;"> <span style="color: rgb(8, 16, 191); font-family: Georgia,serif;">**<span style="color: rgb(8, 16, 191); font-family: Georgia,serif;">converging ** <span style="font-family: Georgia,serif;">and <span style="font-size: 110%; color: rgb(8, 16, 191); font-family: Georgia,serif;">**diverging**.
 * <span style="font-family: Georgia,serif;"><span style="font-size: 132%; font-family: 'Times New Roman',Times,serif;">a <span style="font-size: 90%; color: rgb(8, 16, 191); font-family: Georgia,serif;">**converging lens** <span style="font-size: 91.8%; font-family: Georgia,serif;"> <span style="font-size: 102%; font-family: Georgia,serif;">is thicker in the middle, meaning that the initially parallel rays of light passing through are made to converge (or to meet at a point). in this type of lens, the wave fronts are retarded more through the center of the lens, which allows the light to converge.
 * <span style="font-family: Georgia,serif;"><span style="font-size: 120%; font-family: 'Times New Roman',Times,serif;">a <span style="color: rgb(8, 16, 191); font-family: Georgia,serif;">**diverging lens** <span style="font-size: 120%; font-family: Georgia,serif;"> i <span style="font-size: 120%; font-family: Georgia,serif;">s thinner in the middle and allows for parallel rays of light to be diverged (or to extend from different directions from a point). In this type of lens, <span style="font-size: 110%; font-family: Georgia,serif;">the waves are retarded more at the edges<span style="font-family: Georgia,serif;">.
 * <span style="font-size: 110%; font-family: Georgia,serif;">the most net bending of rays occurs at the outermost prisms, for they have the greatest angle between the two refracting surfaces. not net bending happens in the middle prism because its glass faces are parallel and rays emerge in their original direction <span style="font-size: 120%; font-family: 'Times New Roman',Times,serif;">.
 * <span style="font-family: Georgia,serif;">real lenses are not made of prisms but of a solid glass piece with surfaces that are normally ground down to spherical shape.
 * <span style="font-family: Georgia,serif;">here are some crucial terms that make up a lens:
 * <span style="font-size: 110%; color: rgb(8, 16, 191); font-family: Georgia,serif;">**principle axis** <span style="font-family: Georgia,serif;"><span style="font-size: 120%; font-family: 'Times New Roman',Times,serif;">: this is the line joining the centers of curvature of the surface of the lens.
 * **<span style="color: rgb(8, 16, 191); font-family: Georgia,serif;">focal point **<span style="font-family: Georgia,serif;">: for a converging lens, the point at which a beam of light parallel to the principal axis converges. for a diverging lens,the point from which such a beam appears to come. incident parallel beams that aree not parallel to the principal axis focus at ponts above or below the focal point.
 * **<span style="font-size: 110%; color: rgb(8, 16, 191); font-family: Georgia,serif;">focal plane **<span style="font-family: Georgia,serif;">: a plane passing through either focal point of a lens that is perpendicular to the principal axis. For a converging lens, any incident parallel beam of light converges to a point somewhere on a focal plane. For a diverging lens, such a beam appears to come from a point on a focal plane.
 * <span style="font-family: Georgia,serif;">a lens has two focal points and two focal planes because a lens affects light coming from the right the same way as light coming from the left.
 * **<span style="color: rgb(8, 16, 191); font-family: Georgia,serif;">focal length **<span style="font-family: Georgia,serif;">: whether converging or diverging, the focal length is the distance between the center of the lens and its focal point. when the lens is thin, the focal lengths on either side are equal, even when the curvatures on the two sides are not.

<span style="font-family: Georgia,serif;">**<span style="font-size: 120%; color: rgb(0, 142, 255); font-family: Georgia,serif;">30. 2 Image Formation by a Lens **
<span style="color: rgb(0, 142, 255); font-family: Georgia,serif;">
 * <span style="font-family: Georgia,serif;">with unaided vision, a far away object is seen through a small angle of view but when you are closer, the same object is seen through a larger angle of view. This wider angle enables the perception of more detail. **<span style="color: rgb(8, 16, 191); font-family: Georgia,serif;">Magnification **<span style="font-family: Georgia,serif;"> happens when an image is observed through a wider angle with the use of a lens than without the lens and allows more detail to be seen.
 * <span style="font-family: Georgia,serif;">a **<span style="color: rgb(8, 16, 191); font-family: Georgia,serif;">magnifying glass **<span style="font-family: Georgia,serif;"> is a converging lens that increases the angle of view and allows more detail to be seen. A converging lens will only magnify when the object is between the focal point and the lens, which is why you have to hold the magnifying glass up close to the object you are observing.
 * <span style="font-family: Georgia,serif;">the magnified image will be farther from the lens and will appear right-side up. If a screen were set at the image distance, no image would appear on the screen because no light is actually directed to the image position. However, the rays that reach the eye behave as if they came from the image position, making this image a **<span style="color: rgb(8, 16, 191); font-family: Georgia,serif;">virtual image **<span style="font-family: Georgia,serif;">. A virtual image is formed through reflection or refraction that can be sen by an observer but cannot be projected on a screen because light from the object does not actually come to a focus.<span style="color: rgb(0, 142, 255); font-family: Georgia,serif;">

<span style="color: rgb(0, 0, 0); font-family: Georgia,serif;">http://www.lhup.edu/%7Edsimanek/scenario/labman3/thinlens.htm <span style="font-family: Georgia,serif; color: rgb(0, 142, 255);"><span style="color: rgb(0, 142, 255); font-family: Georgia,serif;"> <span style="color: rgb(0, 0, 0); font-family: Georgia,serif;">http://www.lhup.edu/%7Edsimanek/scenario/labman3/thinlens.htm > > <span style="color: rgb(0, 0, 0); font-family: Georgia,serif;">http://www.lostartofblogging.com/wp-content/uploads/2007/12/magnifying-glass.JPG  <span style="color: rgb(0, 142, 255); font-family: Georgia,serif;"> <span style="color: rgb(0, 142, 255); font-family: Georgia,serif;"> =<span style="color: rgb(0, 142, 255); font-family: Georgia,serif;">30. 3 Constructing Images Through Ray Diagrams = <span style="color: rgb(0, 142, 255); font-family: Georgia,serif;"> <span style="font-family: Georgia,serif;"> <span style="color: rgb(0, 0, 0); font-family: Georgia,serif;">http://facstaff.gpc.edu/~pgore/PhysicalScience/optics.html <span style="font-family: Georgia,serif;">these three paths are shown in the above figure: the image is located where the rays intersect. any two of these rays is sufficient to locate the relative size and location of the image. <span style="color: rgb(0, 142, 255); font-family: Georgia,serif;"> <span style="color: rgb(0, 0, 0); font-family: Georgia,serif;">http://www.antonine-education.co.uk/physics_a2/options/Module_6/Topic_2/Ray_Diag_B1.gif
 * <span style="font-family: Georgia,serif;">when the object is far enough away to be beyond the focal point of a converging lens, light from the object does converge and can be focused on a screen, making this image a <span style="color: rgb(8, 16, 191); font-family: Georgia,serif;">**real image** <span style="font-family: Georgia,serif;">. A real image formed by a single converging lens is upside down or inverted. <span style="color: rgb(0, 142, 255); font-family: Georgia,serif;">
 * <span style="font-family: Georgia,serif;">converging lenses are used in projecting slides and motion pictures on a screen and for projecting a real image on the film of a camera.
 * <span style="font-family: Georgia,serif;">when a diverging lens is used by itself, t**he image result is always virtual, right-side up, and smaller than the object itself.**<span style="color: rgb(0, 142, 255); font-family: Georgia,serif;">
 * <span style="font-family: Georgia,serif;">a simple use for a diverging lens would be for the viewfinder of a camera. When you look through the viewfinder at the object you want to take a picture of, you see a right-side up, virtual image that matches the same proportions as the photograph to be taken.
 * <span style="color: rgb(8, 16, 191);">**r** <span style="color: rgb(8, 16, 191); font-family: Georgia,serif;">**ay diagrams** <span style="font-family: Georgia,serif;">show the principal rays that can be used to determine the size and location of an image.
 * <span style="font-family: Georgia,serif;">in order to construct a ray diagram three things must be known:
 * 1) <span style="font-family: Georgia,serif;">the size and location of the object
 * 2) <span style="font-family: Georgia,serif;">the objects distance from the center of the lens
 * 3) <span style="font-family: Georgia,serif;">the focal length of the lens
 * <span style="font-family: Georgia,serif;">to locate the position of the image,you only have to know the paths of two rays from a point on the object.
 * <span style="font-family: Georgia,serif;">a ray parallel to the principal axis will be refracted by the lens to the focal point.
 * <span style="font-family: Georgia,serif;">a ray of light will pass through the center with no appreciable change in direction. a ray from the tip of the arrow proceeds in a straight line through the center of the lens.
 * <span style="font-family: Georgia,serif;">a ray of light that passes through the focal point in front of the lens emerges from the lens and proceeds parallel to the principal axis.
 * <span style="font-family: Georgia,serif;">in the case where the distance from the lens to the object is less than the focal length, the rays diverge as they leave the lens. the rays of light appear to be coming from a point in front of the lens. the location of the image is found by extending the rays backwards to where they meet.


 * <span style="font-family: Georgia,serif;">the following ray diagrams show image formation by a converging lens as an object initially at the focal point in moved away from the lens along the principal axis. Since the object is not located between the focal point and the lens, all the images that are formed are real and inverted:

1.)<span style="color: rgb(0, 142, 255); font-family: Georgia,serif;">

<span style="font-family: Georgia,serif;"><span style="color: rgb(0, 0, 0); font-family: Georgia,serif;">http://www.antonine-education.co.uk/physics_a2/options/Module_6/Topic_2/Ray_Diag_A3.gif


 * Object Position**: between f and 2f from lens
 * Image Position**: beyond 2f from lens
 * Image size**: magnified

2.)<span style="color: rgb(0, 142, 255); font-family: Georgia,serif;">

<span style="font-family: Georgia,serif;"><span style="color: rgb(0, 0, 0); font-family: Georgia,serif;">http://www.antonine-education.co.uk/physics_a2/options/Module_6/Topic_2/Ray_Diag_A4.gif


 * Object Position**: distance f from lens (at focal point)
 * Image Position**: infinity

3.)<span style="color: rgb(0, 142, 255); font-family: Georgia,serif;"> <span style="font-family: Georgia,serif;"><span style="color: rgb(0, 0, 0); font-family: Georgia,serif;">http://www.antonine-education.co.uk/physics_a2/options/Module_6/Topic_2/Ray_Diag_A2.gif


 * Object Position**: distance 2f from lens
 * Image Position:** distance 2f from lens
 * Image Size**: same as object

4.)<span style="color: rgb(0, 142, 255); font-family: Georgia,serif;"> <span style="font-family: Georgia,serif;"><span style="color: rgb(0, 0, 0); font-family: Georgia,serif;">http://www.antonine-education.co.uk/physics_a2/options/Module_6/Topic_2/Ray_Diag_A1.gif


 * Object Position**: beyond 2f from lens
 * Image Position**: between f and 2f from lens
 * Image size**: smaller

<span style="color: rgb(0, 142, 255); font-family: Georgia,serif;"> <span style="color: rgb(0, 0, 0); font-family: Georgia,serif;">http://www.physics.uq.edu.au/courses/phys1000/optics_raydiag2.png =<span style="color: rgb(0, 142, 255); font-family: Georgia,serif;">30.4 Image Formation Summarized = =<span style="color: rgb(0, 142, 255); font-family: Georgia,serif;">30.5 Some Common Optical Instruments =
 * <span style="font-family: Georgia,serif;">drawing ray diagrams also works for diverging lenses. a ray parallel to the principal axis from the tip of the arrow will be bent by the lens in the same direction as if it had come from the focal point. A ray through the center goes straight through. A ray that is heading for the focal point on the far side of the lens is bent so that it emerges parallel to the axis of the lens.
 * <span style="font-family: Georgia,serif;">the three rays appear to come from a point on the same side of the lens as the object
 * <span style="font-family: Georgia,serif;">this point defines the position of the virtual image
 * <span style="font-family: Georgia,serif;">the image is nearer the lens than the object
 * <span style="font-family: Georgia,serif;">it is smaller than the object and right-side up
 * <span style="font-family: Georgia,serif;">to get a better understanding of how real and virtual images are formed, visit this web page to take a look at ray diagrams for the case of converging and diverging lenses:
 * <span style="font-family: Georgia,serif;">[]
 * <span style="font-family: Georgia,serif;">**Converging lens**: a simple magnifying glass when the object is within one focal length of the lens
 * <span style="font-family: Georgia,serif;">image is virtual, magnified, and right-side up.
 * <span style="font-family: Georgia,serif;">when the object is beyond one focal length = real, inverted image
 * <span style="font-family: Georgia,serif;">the location of the image depends on how close the object is to the focal point. If it is close to the focal point the image is far away ( movie or slide projector)
 * <span style="font-family: Georgia,serif;">if the object is far from the focal point, the image is nearer ( as with a camera)
 * <span style="font-family: Georgia,serif;">in all cases where a real image is formed, the object and the image are on the opposite sides of the lens.
 * <span style="font-family: Georgia,serif;">**Diverging Lens**:
 * <span style="font-family: Georgia,serif;">the image is always virtual, reduced, and right-side up.
 * <span style="font-family: Georgia,serif;">this is true for all locations of object
 * <span style="font-family: Georgia,serif;">in all cases when i virtual image is formed, the object and the image are on the same side of the lens
 * <span style="font-family: Georgia,serif;">camera
 * <span style="font-family: Georgia,serif;">telescope
 * <span style="font-family: Georgia,serif;">compound microscope
 * <span style="font-family: Georgia,serif;">projector

<span style="color: rgb(0, 142, 255); font-family: Georgia,serif;">The Camera:
<span style="font-family: Georgia,serif;">http://www.kenrockwell.com/nikon/d40/images/D3S_2078-600.jpg

<span style="font-family: Georgia,serif; color: rgb(0, 142, 255);"> [] <span style="font-family: Georgia,serif;">

consists of a lens and a sensitive film mounted in a lightweight box. the lens is mounted so that it can be moved back and forth to adjust the distance between the lens and film. the lens forms a real, inverted image on the film.
 * <span style="font-family: Georgia,serif;">most cameras use compound lenses to minimize distortions produced by a lens called <span style="color: rgb(8, 16, 191); font-family: Georgia,serif;">**aberrations** <span style="font-family: Georgia,serif;">.
 * <span style="font-family: Georgia,serif;">the amount of light allowed to pass through is regulated by a shutter and diaphragm.
 * <span style="font-family: Georgia,serif;">the shutter controls the length of time that the film is exposed to light
 * <span style="font-family: Georgia,serif;">the diaphragm controls the opening that light passes through to reach the film

<span style="color: rgb(0, 142, 255); font-family: Georgia,serif;">The Telescope:
<span style="font-family: Georgia,serif; color: rgb(0, 142, 255);">

<span style="font-family: Georgia,serif; color: rgb(0, 142, 255);"> <span style="color: rgb(0, 0, 0); font-family: Georgia,serif;"> http://www.lhup.edu/~dsimanek/scenario/telescop.gif <span style="font-family: Georgia,serif;">

paying attention to the diagram A, it shows a lens arrangement for an astronomical telescope.


 * <span style="color: rgb(0, 0, 0); font-family: Georgia,serif;">a simple telescope uses a lens to form a real image of a distant object
 * <span style="color: rgb(0, 0, 0); font-family: Georgia,serif;">it is projected in space to be examined by another lens used as a magnifying glass
 * <span style="color: rgb(0, 0, 0); font-family: Georgia,serif;">the second lens, called the <span style="color: rgb(8, 16, 191); font-family: 'Courier New',Courier,monospace;">**eyepiece,** is positioned so that the image produced by the first lens is within one focal length of the eyepiece.
 * <span style="color: rgb(0, 0, 0); font-family: Georgia,serif;">the eyepiece forms a larger, virtual image of the real image.
 * <span style="color: rgb(0, 0, 0); font-family: Georgia,serif;">when looking through a telescope, an image of an image is seen.
 * <span style="color: rgb(0, 0, 0); font-family: Georgia,serif;">//astronomical telescopes// produce inverted images, which is why maps of the moon are uspide down.
 * <span style="color: rgb(0, 0, 0); font-family: Georgia,serif;">a third lens (or reflecting prisms) is used in //terrestrial telescopes//, which make an image that is right side up
 * <span style="color: rgb(0, 0, 0); font-family: Georgia,serif;">this type of lens is used in //binoculars//, having a pair of prisms side by side each with a pair of prisms to provide four reflecting surfaces to turn images right side up.
 * <span style="color: rgb(0, 0, 0); font-family: Georgia,serif;">telescopes that use lenses are //refracting telescopes//.

<span style="color: rgb(0, 142, 255); font-family: Georgia,serif;">
<span style="color: rgb(0, 142, 255); font-family: Georgia,serif;">

<span style="color: rgb(0, 142, 255); font-family: Georgia,serif;">The Compound <span style="color: rgb(0, 142, 255);">Microscope:
<span style="font-family: Georgia,serif; color: rgb(0, 142, 255);"> []
 * <span style="font-family: Georgia,serif;">uses two converging lenses of short focal length
 * <span style="font-family: Georgia,serif;">the first lens is called the <span style="color: rgb(8, 16, 191);">**objective lens** and produces a real image of a close object.
 * <span style="font-family: Georgia,serif;">the image is enlarged because it is farther from the lens than the object
 * <span style="font-family: Georgia,serif;">the second lens, the eyepiece, forms a virtual image of the first image, and is enlarged even more.
 * <span style="font-family: Georgia,serif;">this instrument is called a compound microscope because it enlarges an already enlarged image.

<span style="color: rgb(0, 142, 255);"><span style="font-family: Georgia,serif;">The Projector :

 * <span style="font-family: Georgia,serif;">a concave mirror reflects light from an intense source back onto a pair of //condenser lenses//.
 * <span style="font-family: Georgia,serif;">the condenser lenses direct the light through the slide or movie frame to a //projection lens.//
 * <span style="font-family: Georgia,serif;">the projection lens is mounted in a sliding tube so that it can be positioned back and forth to focus a sharp image on the screen.

=<span style="color: rgb(0, 142, 255); font-family: Georgia,serif;">30.6 The Eye: = <span style="color: rgb(0, 142, 255); font-family: Georgia,serif;"> []

<span style="font-family: Georgia,serif;">[]

=<span style="font-size: 90%; color: rgb(0, 142, 255); font-family: Georgia,serif;">30.7 Some Defects in Vision = <span style="font-size: 90%; color: rgb(0, 142, 255); font-family: Georgia,serif;"> <span style="color: rgb(0, 142, 255); font-family: Georgia,serif;">
 * <span style="font-family: Georgia,serif;">the human eye is similar to a camera
 * <span style="font-family: Georgia,serif;">the **<span style="color: rgb(8, 16, 191);">iris **, or colored part of the eye, regulates the amount of light that is permitted to enter the eye through the **<span style="color: rgb(8, 16, 191);">pupil **, or opening through which the light actually passes.
 * <span style="font-family: Georgia,serif;">the transparent covering over top of the eye is called the **<span style="color: rgb(8, 16, 191);">cornea **.
 * <span style="font-family: Georgia,serif;">once the light passes through the cornea, is regulated by the iris, and goes through the pupil, it is focused on a layer of tissue at the back of the eye called the **<span style="color: rgb(8, 16, 191);">retina **, which is extremely light sensitive.
 * <span style="font-family: Georgia,serif;">the retina is not uniform
 * <span style="font-family: Georgia,serif;">there is a spot in the retina where the nerves carrying all the information leave the eye in the bundle which is called the **<span style="color: rgb(8, 16, 191);">blind spot **.
 * <span style="font-family: Georgia,serif;">the<span style="color: rgb(8, 16, 191);">**<span style="color: rgb(8, 16, 191);"> fovea **<span style="color: rgb(8, 16, 191);"> is the small region in the center of the field of view where there is the most distinct vision; this is where much more detail can be viewed than at the sides of the eye
 * <span style="font-family: Georgia,serif;">in both the camera and the eye the image is upside down and is able to be altered for both:
 * <span style="font-family: Georgia,serif;">in a camera you can turn the film around to observe it
 * <span style="font-family: Georgia,serif;">in the eye, your brain has learned to turn around the images it receives from the retina
 * <span style="font-family: Georgia,serif;">in the eye, most of the focusing is done by the cornea
 * <span style="font-family: Georgia,serif;">adjustments in focusing of the image on the retina are made by changing the thickness and shape of the lens to regulate its focal length which is called //accommodation// and happens courtesy of the //ciliary muscle// which surrounds the lens.
 * <span style="font-family: Georgia,serif;">the eyes of a farsighted person form images behind the retina because the eyeball is too short
 * <span style="font-family: Georgia,serif;">farsighted people have to hold objects more than 25 cm away to be able to focus on them
 * <span style="font-family: Georgia,serif;">the remedy is to increase the converging effect on the eye by wearing eyeglasses or contact lenses with converging lenses
 * <span style="font-family: Georgia,serif;">this will converge the rays that enter the eye sufficiently to focus them on the retina instead of behind the retina.
 * **<span style="color: rgb(8, 16, 191); font-family: Georgia,serif;">farsightedness and nearsightedness **:

<span style="font-family: Georgia,serif;">

<span style="color: rgb(0, 0, 0); font-family: Georgia,serif;">[] <span style="color: rgb(0, 142, 255); font-family: Georgia,serif;">


 * **<span style="color: rgb(8, 16, 191); font-family: Georgia,serif;">nearsighted **<span style="font-family: Georgia,serif;"> people can see nearby objects clearly, but does not see distant objects clearly because they are focused too near the lens, in front of the retina because the eyeball is too long
 * <span style="font-family: Georgia,serif;">
 * <span style="font-family: Georgia,serif;"><span style="color: rgb(8, 16, 191);">**Astigmatism** i s ad effect of the eye that is a result of the cornea being curved more in one direction than the other
 * <span style="font-family: Georgia,serif;">the eye then cannot form sharp images
 * <span style="font-family: Georgia,serif;">wearing corrective cylindrical lenses that have more curvature in one direction would be a solution to this defect

<span style="font-family: Georgia,serif;"> *

<span style="color: rgb(0, 142, 255); font-family: Georgia,serif;">
=<span style="color: rgb(0, 142, 255); font-family: Georgia,serif;">30. 8 Some Defects of Lenses = <span style="font-family: Georgia,serif; color: rgb(0, 142, 255);"> <span style="color: rgb(0, 0, 0); font-family: Georgia,serif;">[]
 * <span style="font-family: Georgia,serif;">**<span style="color: rgb(8, 16, 191);">Aberrations ** are the distortions of an image, because no lenses produces a perfect picture
 * <span style="font-family: Georgia,serif;">in order to eliminate this problem some lenses can be combined in certain positions to fix it, most optical instruments use compound lenses that consist of several simple lenses
 * <span style="font-family: Georgia,serif;">//Spherical aberration// happens when light passes through the edges of a lens and focuses at a different place from light passing through the center of the lens
 * <span style="font-family: Georgia,serif;">this can be revised by covering the edges of a lens
 * <span style="font-family: Georgia,serif;">in optical instruments, it is revised by a combination of lenses
 * <span style="font-family: Georgia,serif;">//Chromatic aberration// is a result of the different speeds of light of various colors and the different refractions that take affect on them
 * <span style="font-family: Georgia,serif;">through out a simple lens blue and red light bend by different amounts so they do not focus in the same spot
 * <span style="font-family: Georgia,serif;">//Achromatic lenses// correct this defect due to the combination of simple lenses of different types of glass
 * <span style="font-family: Georgia,serif;">vision is sharpest in the eye when the pupil is the smallest it can be
 * <span style="font-family: Georgia,serif;">this is so because light then passes through only the center of the eye's lens in which spherical and chromatic aberrations are limited
 * <span style="font-family: Georgia,serif;">light bends the least through the center of the lens so less focusing is required for a sharp image
 * <span style="font-family: Georgia,serif;">vision is better in bright light as opposed to darkness because your pupils are smaller
 * <span style="font-family: Georgia,serif;">in today's world, eyeglasses and contact lenses are becoming more and more of a thing of the past
 * <span style="font-family: Georgia,serif;">surgeons are able to reshape the cornea of the eye which allows for normal vision, via experimental techniques

<span style="font-family: Georgia,serif;">
 * Works Cited:**

<span style="font-family: Georgia,serif;">All information gathered was courtesy of the text book and outside sources: Hewitt, Paul G. __Conceptual Physics__. Third Edition ed. Menlo Park, California: Scott Foresman Addison Wesley, 1999.

__How Does the Human Eye Work?__ 1998-2003. Pasadena Eye Associates. 28 May 2009 <http://www.pasadenaeye.com/faq/faq15/faq15_text.html>.

<span style="font-family: Georgia,serif;">__Lens (optics)__. Wikipedia. May 2009 <http://en.wikipedia.org/wiki/Lens_(optics)>.

http://hyperphysics.phy-astr.gsu.edu/hbase/geoopt/lenscon.html

<span style="font-family: Georgia,serif;">
<span style="color: rgb(0, 142, 255);"> <span style="font-family: Georgia,serif;"> <span style="color: rgb(0, 142, 255);">