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. D

    Focal Length of a Diverging Lens

    Homework Statement An object that is 6.00 cm tall is placed 40.0 cm in front of a diverging lens. The magnitude of the focal length of the lens is 20.0 cm. Find the image position and size. Is the image real or virtual? Upright or inverted? Homework Equations / The Attempt at a...
  2. N

    Solving for p: Finding Distance from Convex Lens

    Homework Statement Given only the distance between the object and its image (p +q), how is it possible to find p, the distance of the object from the convex lens? Homework Equations 1/p + 1/q = 1/f in this case, p + q =40 also, the image is smaller than the original, so p > 2f The...
  3. J

    Can a Simple Glass Lens Focus White Light Correctly?

    Homework Statement The property of a transparent material that makes it useful for a lens is: this is refraction, right? In relation to this, the image of an object can't be focused correctly if a simple glass lens is placed under white light because: a)the lens absorbs light b)the glass...
  4. R

    Determine the focal length of a lens

    Homework Statement A 2.0-cm-diameter spider is 2.0 {\rm m} from a wall. Determine the focal length of a lens that will make a half-size image of the spider on the wall. Determine the position (measured from the wall) of a lens that will make a half-size image of the spider on the wall...
  5. D

    How Do You Calculate Image Distance and Height Using Lenses?

    Lens Help Needed! A converging lens with a focal length of 50cm and a diverging lens with a focal length of -52 cm are 227cm apart. A 3.9-cm-tall object is 70cm in front of the converging lens. Calculate the distance between image and diverging lens. Express your answer using two...
  6. M

    How to Calculate Radii for a Symmetric Converging Lens to Double Image Size?

    Homework Statement An object is 34.0 cm from a screen. What are the radii of a symmetric converging plastic lens (i.e., two equally curved surfaces) that will form an image on the screen twice the height of the object? (Take the index of refraction of plastic to be 1.59.) Homework...
  7. J

    Why Are Both X- and Y-Intercepts Equal to 1/f in the Lens' Equation?

    For the Lens' equation 1/f = 1/u + 1/v why can both the x- and y-intercepts be considered equal to 1/f?
  8. D

    How Is Object Distance Calculated for Image Reduction with a Diverging Lens?

    Homework Statement An object is 18 cm in front of a diverging lens that has a focal length of -12 cm. How far in front of the lens should the object be placed so that the size of its image is reduced by a factor of 2.0 Homework Equations The thin lens equations: (1/di)+(1/do)=1/f...
  9. D

    What is the Relationship Between the Mirror Equation and the Lens Equation?

    Homework Statement Show that the mirror equation can be derived using the same principles that were used in deriving the equation for lenses. Homework Equations \frac{1}{f}=\frac{1}{d_{o}}+\frac{1}{d_{i}} The Attempt at a Solution There really doesn't appear to be any work to put...
  10. J

    How Do Corrective Lenses Affect Vision in Myopia?

    Sufferers of myopia, nearsightedness, have difficutly resolving distant objects because the lenses in their eyes are too strong. If a myopic person has a prescription of -5 diopters, what image do her corrective lenses crate for distant objects? P=1/f I tried this problem and got an...
  11. M

    Geometric optics - why pinhole bends rays like lens

    We were discussing in an https://www.physicsforums.com/showthread.php?t=284322" that pinholes work like lenses, in that they form inverted real images. The other day, a friend told me, that pinholes even do bend the light rays like a lens do. I can - as being nearsighted - actually use a pinhole...
  12. F

    Thin lens equation with multiple lenses

    Homework Statement Heres the problem exactly as written: A system of lenses is composed of three lenses. Calculate the maximum magnification these three lenses will achieve if the lenses are located 35.0 cm apart. The lenses have focal lengths of 15.0, 20.0, and 25.0 cm.Homework Equations 1/p...
  13. M

    Geometric optics - why inverted image from thin lens

    Three questions: 1) Anyone have a pedagogic answer to why the image formed by a thin lens is inverted (i.e. upside-down)? I realize that to get a focused image, the lens has to converge the rays one way or another, so then, eventually, the rays have to cross the optic axis, which in turn...
  14. T

    Can a Lens be Designed to Focus an Electric Field on a Specific Region?

    Hii all.. Is it possible to design a lens(using magnetic fields, dielectric media etc) so as to focus an existing electric field on to a localized region on a electrode. I hope the following picture illustrates what I am trying to do. What I need is a electric field which is considerably...
  15. H

    Mathematical shape for a lens with no spherical aberration

    I'm trying to construct a lens model, and having trouble because I want to portray a perfect lens rather than one with spherical aberration. It's proved impossible to find via Google, although I did find an earlier thread on this forum that was helpful. From what I can gather, the lens needs...
  16. R

    Finding the Optimal Lens Position for a Sharp Image of a Candle

    A candle is placed 1.8 m from a screen. whereshould a lens of focus length 21 cm (0.21 m) be placed between the screen and the candle to prduce a sharp image screen? The only formula i could think of was 1/f=1/do+1/di I've now spent 3 hours on this (test tomorrow) and still don't know...
  17. A

    I'm new to optics: on lens please

    Hi there, I found myself stuck to a simple question really. Trying to find a solution on my own doesn't guarantee a success. Therefore I would appreciate if any of you can offer me helps to solve the following questions. 1. how big a image a lens can see? You see, when you put the image at...
  18. A

    Calculating Sideways Force on Lens from Laser Power

    Homework Statement A laser of power P with wavelength \lambda is directed through a lens (focal length f) off the optical axis by a distance d. What is the sideways force on the lens? Homework Equations Not sure. The average radiation pressure is I/c, where I is the intensity. But this...
  19. N

    How to Find the Waist of a Gaussian Beam at the Focus Using a Lens?

    Homework Statement Hello, I'm really confused about this one, =( Suppose I have a guassian beam that is colliminated (beam expanded) and then suppose i let it passed through a lens to focus it. Given an initial waist and focal length of the lens. How can i find the waist (or half width)...
  20. C

    Einzel Lens Operating Principle

    I'm trying to design an Einzel lens to focus an ion beam. The literature seems pretty consistent that the beam diverges in the first gap and converges in the second gap. (Gaps are between the three electrodes.) What I don't understand is that the potential is lowest at the centre of a...
  21. Shackleford

    Find Final Image Location & Magnification in Lens Combination 21

    21. Two 25cm focal length converging lenses are placed 16.5cm apart. An object is placed 35cm in front of one lens. Where will the final image formed by the second lens be located? What is the total magnification? HERE IS WHAT I NEED CHECKED. Because the image formed by the first lens is on...
  22. J

    Finding the Distance for Enlargement with a Thin Lens

    If you want to produce an image of a bulb that is enlarged by a factor of 2, how far from the wall should the lens be placed. Focal length is 40cm. I know you use 1/d_o + 1/d_i =1/f and m= -d_i/d_o but how do you find d_o? -2/d_o +1/d_o =1/f ? but it comes out to 40cm and not 60cm...
  23. E

    Diverging Spherical Lens Proof

    Homework Statement Using the thin-lens equation and the magnification factor, show that for a spherical diverging lens the image of a real object is always virtual, upright, and reduced? Homework Equations Thin lens equation 1/p + 1/i = 1/f p = distance of object from the lens i =...
  24. J

    Calculating the Final Image Location in a Compound Lens System

    Homework Statement A compound lens system consists of two converging lenses, one at x= -20cm with focal length f1 = +10cm, and the other at x= +20cm with focal length f2 = +8cm . An object 1 centimeter tall is placed at x = -50cm. What is the location of the final image produced by the...
  25. A

    Focal length of concave lens experiment

    Is there any way to find rough focal length of concave lens and convex mirror without using convex lens? Though I did the experiments(with object and image needles, not candle) very carefully with no parallax errors during my practical class, my readings are incorrect. I want to know if der s...
  26. S

    Lens and Focal Length Practice Problems

    Homework Statement A 2.0-cm-diameter spider is 1.80 m from a wall. A. Determine the focal length of a lens that will make a half-size image of the spider on the wall. B. Determine the position (measured from the wall) of a lens that will make a half-size image of the spider on the...
  27. G

    Which Lens Equation Should I Use for This Optics Problem?

    My teacher assigned us 2 problems to do that were the exact same. One he wanted us to use the thin lenses equation, and the other he wanted us to use think lens equation. i need help becuase I don't know which one I am doing wrong and my answer is not lining up as it should, since they are the...
  28. G

    Need help focusing IR using a fresnel lens

    Hello everyone, I want to focus IR on a small rectangular area using a Fresnel lens. I tried trial and error to find the focal point of the lens but can't seem to be able to get the exact point. The frensnel lens is a multiple fresnel lens. Can anyone please help? Thanks =)
  29. L

    How Deep Does the Penny Appear in a Layered Liquid Tank?

    Homework Statement A 15-mm-thick layer of water (n = 1.33) floats on a 60-mm-thick layer of carbon tetrachloride (n = 1.46) in a tank. A penny lies at the bottom of the tank. At what depth below the top water surface do you perceive the penny? (Hint: Use the result and assumptions of Problem...
  30. C

    How to Put a Lens: Facing or Away from Object?

    I'm not sure does which surface facing the object matters? For example, http://micro.magnet.fsu.edu/optics/lightandcolor/images/lensesfigure2.jpg for b) should I put the bulging surface of the convex mirror facing the object or away from the object? I mean are there any rules...
  31. M

    Dimensional Analysis of a lens

    Hello everybody, I am taking a basic undergrad General Chemistry I course and am just having a little trouble brushing myself up on dimensional analysis (or factor label). This is the problem. The area of a telescope lens is 7903 mm2. (a) What is the area in square feet? (b) If it takes a...
  32. R

    Calculating Slide Distance from Projector Lens & Image Dimensions on Screen

    the dimensions of the picture on a 35mm color slide are 24X36 mm,an image of the slide is projected on a screen 9.00 m from the projector lens.the focal length of projectorlens is 150mm. 1-- how far is the slide from the lens 2-- what are the image on the screen. Plz some body help me...i m...
  33. E

    Find Focal Length of Lens When Moving From 20cm to 15cm

    If a lens is moved towards the object from a distance of 20cm to 15cm, the magnification of the image remains the same. What is the focal length of the lens? Sorry I am new here so please forgive me if I have violated any rules.:cry:
  34. K

    What is the minimum image-object distance in a single lens system?

    Homework Statement For a system with a single lens, what is the smallest image to object distance that you can achieve? Homework Equations I guess (1/f)=(1/i)+(1/o) The Attempt at a Solution Tried drawing a few ray diagrams but didn't seem to get anywhere :S
  35. L

    Optics question: What two positions of a lens gives a sharp image?

    1. A lamp and a screen are 1m apart and a +4.5 D thin lens is mounted between them. Where must the lens be placed in order to produce a sharp image on the screen, and what will be the magnification? 2. Gauss Law: L' = L + F 3. I attempted this question by using the Gauss Law but I...
  36. G

    Lens & Focal Point System: Image Formation

    Homework Statement I have a two lens system (both are convex lens; converging lens). Say I set lens 1 on left hand side and lens 2 on the right hand side. A)If I place an object within the focal point of lens 1 and the image create by this lens is OUTside the focal distance of lens 2, what...
  37. G

    Magnification in a Convex Lens: + or -?

    In a conversing lens, if the object is not within the focal point, then the magnification is "-". But in the case where the object is placed in the focal point, then the magnification is "+"?
  38. C

    Location final image diveraging and converging lens

    Homework Statement A 1.5 cm tall object is placed 0.50 m to the left of a diverging lens with a focal length of 0.20 m. A converging lens with a focal length of 0.17 m is located 0.08 m to the right of the diverging lens. a)What is the location of the final image with respect to the object...
  39. G

    Creating an Image 2x Size of Object w/ Convex Lens: Half Focal Length Away

    Homework Statement A converging lens (convex lens) creates an image that is 2 times the size of the object. The object is placed: Homework Equations -di/do = hi/ho 1/f = 1/di + 1/do The Attempt at a Solution I thought the answer was that the object is place two focal lengths...
  40. M

    Is a Fresnel Lens a Better Option for Solar Thermal Applications?

    I would like to know if anybody has thoughts on this idea, vs using parabolic dishes and a distributed oil heat transfer system for solar thermal applications. I can find cheap fresnel lens', and I would like to use them to concentrate the light, then columnate it so that many concentrated...
  41. K

    Analyzing Errors in Converging Lens Calculations

    Homework Statement My task was to determine the focal distance and the magnification of a converging lens. I've done everything as stated in the procedure. The problem that i have is that when i am calculating the magnification in two differents ways i.e M1=b/a and M2=h'/h where a=distance...
  42. W

    Draw Double Concave Lens Diagram

    Homework Statement "Please draw an image for a double concave lens with the object paced between the lens and the focal point. Remember to show all the required rays, their direction, and the focal point of your lens" Homework Equations no equations needed. The Attempt at a...
  43. J

    Find the focal length of a concave lens using a convex lens?

    Can anyone explain to me the procedure that one would follow to you find the focal length of a concave lens using a convex lens? Thanks.
  44. L

    Distance between the object and the lens

    Homework Statement A diverging lens of 6 mm focal length produces an image of magnification m = 1/2. What is the distance between the object and the lens?
  45. redtree

    Does gravity function as a lens, a prism or both?

    Does gravity function as a lens, a prism or both?
  46. J

    Which Focal Length is Longer for Different Light Colors?

    Homework Statement 1. A converging lens is used to focus parallel beams of red light and then later used to focus parallel beams of green light. Which focal length is longer? Explain 2. A photographer moves closer to his subject & then refocuses the camera. Is the camera lens now closer...
  47. J

    Solve Concave Lens Problem: Step-by-Step Guide

    Homework Statement http://img215.imageshack.us/img215/8457/physicsol4.jpg Homework Equations n1sin01=n2sin02 1/f = (n-1)(1/r1-1/r2) The Attempt at a Solution I'm really jus confused with this problem I don't really see where to start. I'm assuming the fish bowl is a...
  48. S

    Radii of Bright Fringes in Reflected Light for Plano-Convex Lens

    Homework Statement A plano-convex glass lens of radius of curvature 2.6 m rests on an optically flat glass plate. The arrangement is illuminated from above with monochromatic light of 565-nm wavelength. The indexes of refraction of the lens and plate are 1.6. Determine the radii of the first...
  49. A

    What lens shape gives perfect focus?

    Assuming ray optics model is valid, what lens profile focuses light to a point? It must not be spherical, otherwise there would not be the term 'spherical abberation'.
  50. P

    Convex Lens and Light Refraction

    Hi all, if light was to go straight through a convex lens would it come out straight or inverted to a point? also if light was to go through the same lens but goes through going inwards how would the light be refracted?
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