Lens Definition and 835 Threads

A lens is a transmissive optical device that focuses or disperses a light beam by means of refraction. A simple lens consists of a single piece of transparent material, while a compound lens consists of several simple lenses (elements), usually arranged along a common axis. Lenses are made from materials such as glass or plastic, and are ground and polished or molded to a desired shape. A lens can focus light to form an image, unlike a prism, which refracts light without focusing. Devices that similarly focus or disperse waves and radiation other than visible light are also called lenses, such as microwave lenses, electron lenses, acoustic lenses, or explosive lenses.
Lenses are used in various imaging devices like telescopes, binoculars and cameras. They are also used as visual aids in glasses to correct defects of vision such as myopia and hypermetropia.

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  1. P

    An optics problem - elliptical lens and plane waves

    Homework Statement I must show that a point source placed at one of the focii will produce a plane wave (or vise versa) when the light is refracted through the interface. This problem is really kicking my ***, I've spent at least three hours trying to figure out different ways to do it...
  2. P

    Why Do Sunglasses Have Zero Power?

    I have an interestng question. Though sunglasses have curved surfaces-why they have zero power? Can u answer me?
  3. W

    Calculate Lens Focal Length - Convex & Concave Lenses

    Homework Statement I have an actually interesting practical homework. I need to calculate the optical strength (hope I translated it right, D=1/F), to do I need to find the lens focal length. I need to find my self a concave and a convex lens. I don't have a concave lens (I think), but I do...
  4. M

    Ray Diagram: Small Bulb & Convex Lens

    Homework Statement A small bulb is placed in front of a convex lens. a) Suppose that the bulb is placed as shown. Using all three principal rays, draw an accurate ray diagram to determine the location of the image. Label the image location...
  5. O

    Deriving Focal Length for a Thick Lens

    Homework Statement Derive 1/f = (n-1)*( (1/r1)-(1/r2)+(((n-1)t))/(nr1r2))) using the ray matrix method. Homework Equations Matrix for curved dielectric interface: M1 = [1, 0] [(1/r)(n1/n2 - 1), n1/n2 ] Matrix for translation through homogeneous medium: M2 = [1, d] [0...
  6. D

    Help with Ray Diagrams for Lens and Mirror Systems

    hello, my professer has been getting us to draw ray diagrams of two lens systems and diagrams of a lens and mirror system. these are two situations that i can not seem to figure out for my self two lens system : diverging lens to converging lens (pictures would be ideal)...
  7. C

    Finding the thickness of a double convex lens

    Homework Statement A double convex lens has a diameter of 5 cm and zero thickness at its edges. A point object on an axis through the center of the lens produces a real image on the opposite side. Both object and image distances are 30 cm, measured from a plane bisecting the lens. The lens has...
  8. S

    What is the field of view for the low power lens

    Homework Statement A high end microscope with a total power magnification of 1500x has a field of view of 120 micrometers. when fitted with a new objective with a low power lens, the total magnification is 900x. what is the field of view for the low power lens? Homework Equations...
  9. S

    Lens: object distance vs. image distance?

    Homework Statement An object is at distance s from a thin glass lens of focal length f. The lens is surrounded by air. The image is at distance s' from the lens. Draw a graph of s' versus s. Explain physically why the graph varies as it does. Homework Equations I think I am...
  10. P

    Making a Fresnel Lens for Solar Water Purification

    i want to do a project on solar water purification. I just saw a video on purifying water using fresnel lens. However, i haven't found any information on how one can make a fresnel lens suited to the purpose. So, how does one make a fresnel lens?
  11. D

    Fresnel Lens Optics - Questions & Answers

    Hello :) I search for some specific info about fresnel lenses. I bought few so called "fresnel lenses" to play with light in my photography studio. I have both real fresnel lens (wide) and just magnifical foil (narrow). I want to project some pattern, so I put fresnel lens in front of...
  12. A

    Deriving the lens formula for a convex lens-say

    I will be thankful if the following points are clarified. 1. While deriving the lens formula for a convex lens-say, 1/f= 1/v - 1/u where u and v are the object and image distances, the minus sign is obtained after applying sign conventions. But, I don't understand the logic behind taking the...
  13. K

    How to Solve a Converging Lens Problem?

    Homework Statement There is an object 20 cm from a converging lens with a 10 cm focal length. Homework Equations Is the image upright or inverted? Calculate the image distance. Calculate the image height. The Attempt at a Solution I just had this on a college test in a...
  14. R

    What Software Can Design a High-Accuracy Collimator Lens?

    Hi I want to make a high accuracy collimator lens, such that it collimates ( with divergence angle < 1 micron) a beam of light coming from the focal plane but from off axis points as well ( -delta to + delta, where delta is in microns). Sugest some suitable softwares (along with the link)...
  15. Z

    Plano-Convex lens cut in two halves

    Homework Statement A thin plano-convex lens of focal length f is split into two equal halves. One of the halves is shifted along the optical axis as shown. The separation etween the object and the image planes is 1.8m and the magnification of the image formed by one of the half lens is 2...
  16. fluidistic

    What is the mathematical expression for the index of refraction in a GRIN lens?

    Homework Statement I must calculate the focal length of a GRIN lens. I.e. a lens which radii of curvature are both infinite. I will consider the refractive index to be varying in function of y (the height in the x-y plane). Say I'm given that at y=0, n(0)=n_0. I'm not sure how to write...
  17. D

    Finding Image for a Thick bi-concave Lens

    Homework Statement A bi-concave lens (n=2) has radii of 15cm and 25cm, and an axial thickness of 6-cm. Use the thin-lens equation to see how far off it is in determining the final image location. Homework Equations n1/so + n2/si = (n2 – n1)/R; (n-1)(1/R1 – 1/R2) = 1/f The...
  18. A

    Finding Distance of Retina from Lens: Power from 40D to 44D

    Homework Statement The accomodation power of a boy whose far point is at infinity can vary from 40D to 44D. Using this data find the distance of the retina from the lens. Homework Equations Power of lens,P = 1/f(in meters) f = focal length lens formula, 1/v - 1/u = 1/f The Attempt at...
  19. M

    Lens calculation problem (Optics)

    I'm building a light source for photography and I'm trying to calculate the focal length for a lens that will give me a 40 degree (full width) cone beam from a LED emitter. See attached image. [PLAIN]http://dl.dropbox.com/u/2301/LEDOpticDrawing.jpg The emitter itself measures about 0.5 x...
  20. A

    Medical Eye Lens Structure: Circular & Radial Fibres

    I just studied the structure of the lens of the eye. And I found out that there are two type of fibres present, which were the Circular Fibres and the Radial Fibres. Can anyone please tell me what is the purpose or function of these two fibres ? Or simply they are just fibres which are...
  21. A

    Lens to increase angular responsivity of optical sensor

    How to specify a lens to increase angular responsivity of optical sensor? Sensor I presently use has angular responsivity +/-60 degrees at 50% level and I would like to increase it to +/- 80 degrees at 50% level or more. Which lens should I use? Please advice on design guidance for this...
  22. I

    Why Must Lens Separation Be Considered in Multiple Lens Systems?

    Homework Statement Two 28.0-cm-focal-length converging lenses are placed 16.5 cm apart. An object is placed 36.0 cm in front of one lens. Where will the final image be formed by the second lens? Homework Equations 1/do + 1/di = 1/f The Attempt at a Solution for the first...
  23. I

    Calculating Object Distance for Magnified Real and Virtual Images

    Homework Statement (a)How far from a 50.0-mm-focal-length lens must an object beplaced if its image is to be magnified 2.00 x and be real? (b)What if the image is to be virtual and magnified 2.00x? Homework Equations m = -di/do 1/do+ 1/di = 1/f The Attempt at a Solution m...
  24. I

    Where is the final image in a 2 lens optics problem?

    Homework Statement We have a convex lens with a focal length of 8cm, which is 12cm from the second converging lens that has a focal length of 4cm. An object is 12cm from the first lens. Where is the final image? Homework Equations 1/do + 1/di = 1/f The Attempt at a Solution So...
  25. T

    Nonreflecting coating on a lens

    Homework Statement A transparent film (n = 1.6) is deposited on a glass lens (n = 1.76) to form a nonreflective coating. What is the minimum thickness that would minimize reflection of light with wavelength 500 nm in air? Homework Equations wavelengthXfrequency=c/n (Not sure if that's...
  26. S

    Proposal for measurement of Lens Thirring effect

    I don't possesses enough knowledge of GR to know if this proposal is feasible (or even remotely possible) I would welcome any constructive criticism of the following idea for detecting Lens Thirring effect: Apparatus consists of a dense, massive sphere or disc, rotating at high velocity...
  27. fluidistic

    Thick lens problem, transfer matrices

    Homework Statement A biconconvex (n_l=1.5) lens have radii worth 20 and 10 cm and an axial width of 5 cm. Describe the image of an object whose height is 2.5 cm and situated at 8 cm from the first vertex.Homework Equations Transfer matrices. The Attempt at a Solution I used the ray transfer...
  28. fluidistic

    Geometrical optics, lens and image

    Homework Statement What should be the focal distance of a negative thin lens such that there's a virtual image situated at 50 cm from the lens, of an ant at 100 cm from the lens? Given that the ant is at the right side of the lens, localize and describe the image. Homework Equations...
  29. S

    Lens shapes other than conic sections

    This is just a curiosity question. Are there lens shapes different than just conic sections? Any research or any found applications?
  30. J

    Prove a lens must always be converging if

    Prove a lens must always be converging if... Consider a single lens with the object on the left side. Prove that for an upright, enlarged image that the lens must always be converging. I'm assuming my professor wants this to be mathematically proven, but I have no idea how to do so...HELP! I...
  31. Z

    Are Back & Front Focal Lengths Equal for Thick Lenses?

    Homework Statement is the back focal length equal to the front focal length of a thick lens ie a thick plano convex lens? i know it is not but do not know how to clarify it please help Homework Equations The Attempt at a Solution
  32. P

    Creating a Converging Lens for Sound Waves at the Exploratorium in San Francisco

    How can converging lens for sound waves be made? I got confused because i don't which materials should be used to make such lens. The lens if kept in air cannot be made of a solid material as sound travels faster in solid than in air and thus sound would not be converged. I have read that...
  33. K

    Lens that will make the rays parallel to each other

    i need a lens that will make the rays parallel to each other & focal point at infinite.without much loss in the intensity.collimator lens kind of action but not at the cost of intensity.
  34. S

    Convex lens questionCant find the equation i need. Please help

    A convex lens of focal point 0.8m focuses a real image of the moon onto a screen. If the moon subtends an angle of 0.5 degrees to an observer on earth, calculate the size of the moons image on the screen? Thats the question guys, I am really struggling to find the appropriate equation as we...
  35. T

    Why doesn't a biconvex lens cancel itself out and not change the light beam?

    When you have a biconvex, i.e. two convex lens' back to back, doesn't the light beam just come out straight? Since one convex lens is back to back with another, essentially it is a convex lens, followed by a concave lens. The light would first hit the convex lens, and the light would...
  36. A

    How Does Bisecting a Lens Affect Its Focal Length?

    1)Why when a convex lens having radius of curvature R, focal length f and refractive index μ is bisected horizontally along the principal axis its focal length remains the same, whereas when it is bisected vertically focal length becomes 2f? Does the same thing happens in the case of...
  37. M

    Solving Optic Lens Problem: Find Object Distance for Magnification of 75

    Homework Statement Suppose we have a microscope made out of two lenses, both with a focal length of 25mm, placed 36.5mm apart. Find how far in front of the first lens should the object be placed to assure that the image is magnified at least by a factor of 75? One more: Suppose that...
  38. F

    How Effective Is a Fresnel Lens in Transporting Light Through Fiber Optics?

    Hello, I have a 12x12" fresnel lens and I want to place a 14mm diameter fiber optics cable at the focal point to transport the light ~2.5 ft. Would there be any heat loss? And what percentage of the light would exit the fiber optics? Thanks, Fritz Laun
  39. B

    Brightness of real images from converging lens

    Hi, Have a question about images from a converging lens. I assume that the brightness of the (real) image projected on a screen depends upon the amount of light rays going through the lens - more rays -> brighter. So a larger lens should bring about a brighter image. Ok, now let's go the...
  40. C

    Telephoto lens and focal length being longer that single lens.

    1. Why is a telephoto lens considered to have a longer focal length than that of a single convex lens? A lens combination, such as a diverging and a convex lens, is referred to as a telephoto lens. Suggest why a telephoto lens is considered to have a longer focal length than that of a single...
  41. C

    Why Does a Telephoto Lens Have a Longer Focal Length Than a Single Convex Lens?

    1. Why is a telephoto lens considered to have a longer focal length than that of a single convex lens? A lens combination, such as a diverging and a convex lens, is referred to as a telephoto lens. Suggest why a telephoto lens is considered to have a longer focal length than that of a single...
  42. A

    What is an electron lens diameter?

    On a computer simulation (Simion - ion simulating program) I've got two cylinders (with a small gap between them) through which an electron beam goes through. I understand that the "lens" refers to the equipotential lines, since they form a bulge at each end, just like an optical lens. What does...
  43. S

    Is the Fate of the Universe Truly Determined by Dark Energy?

    The BBc just publsihed this story: http://www.bbc.co.uk/news/science-environment-11030889 The conclusion is: "Professor Priyamvada Natarajan of Yale University, a leading cosmologist and co-author of this study, said that the findings finally proved "exactly what the fate of the Universe...
  44. S

    Doubt with power of lens with 2 media

    This is more of a general question. Suppose there is a biconvex lens(Radii are R1 and R2) with Refractive index =n2,it is bounded on 2 sides by media of RI=n1,n3. Now if I have to find its focal length, 1/f=(n2-n1)/R1+(n2-n3)/R1. Is it correct? Suppose it were correct, If there is a...
  45. T

    Understanding Lens Separation for Creating an Image at Infinity

    Homework Statement The lenses are separated by 250mm. Where should the object be places so that the final image is formed at infinity? I'm confused.
  46. J

    Optics question - eyes and cameras, and the mythical 50mm lens

    Eyes and cameras - a topic that has been troubling me Hi all. This is my first post. I'm seriously thinking about applying to optometric college in the fall. I'm trying to improve my knowledge as much as possible of the area, and one question that keeps coming up (I'm a hobby photographer...)...
  47. F

    Fresnel Lens Array - Focal Point Question

    Hello, all, I am using 9 fresnel lenses (~1x1' per lens) and 9 water blocks for a solar water heater. Each fresnel lens is positioned so that a water block below is heated. A pump is used to pump the water through the system. However, I have one question... I have all of my fresnel...
  48. H

    Design a Flashlight LED Reflector Lens for Flooding

    I'm designing a flashlight using a new LED reflector. It creates a good spot, but I want it to flood on the edges. See image below. My thought was to create a lens and put it in front of the LED reflector to disperse the light around the edges. Can anyone point me to some simple tools that will...
  49. S

    Estimating image distance in lens and mirror

    I'm having difficulty understanding how to estimate the location of an image in a lens/mirror. I tried understanding it by going off the books question/answer section: "A spherical concave lens has a focal length of 16 cm, and an object is placed 8 cm from the lens." It says the answer is...
  50. K

    HELP Finding the focal length of a lens, I'm totally stuck

    Homework Statement A slide projector needs to create a 81 cm high image of a 2.0 cm tall slide. The screen is 360 cm from the slide. Assume that it is a thin lens. What focal length does the lens need? How far should you place the lens from the slide? Homework Equations 1/f = 1/s +...
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