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. O

    Optics Question, where is the lens

    Homework Statement A 3 cm tall object is placed 11 m from a wall. If the image is to be projected upside down with a 20 cm focal lense, what is: A} The type of lens used? B] Where is the lens placed? C] What is the height of the image? D] What is the magnification of the...
  2. R

    Electromagnetic lens for an SEM

    Does anyone know how the machining tolerance in the construction of an electromagnetic lens affects resolution in a scanning electron microscope?
  3. A

    Calculating distance of image from lens

    Homework Statement An object is placed on the optic axis and in front of a converging lens of focal length 38 cm such that its image size is 1.5 times the object size. Calculate the distance of the image from the lens. Express your answer in centimeter. Homework Equations 1/f=1/di +...
  4. S

    Engraving laser machine with a lens

    Hi I have a laser beam(engraving laser machine) and then use a lens for focus the beam but my lens has a crack on the center of lens and when i use my laser in high power the beam diameter will bigger and burning area zone is bigger so: 1- Does the crack doesn't let the maximum focus?in law or...
  5. H

    Choosing the Right Fresnel Lens for Automotive Headlamp Projection?

    Hello, I'm working with an automotive headlamp and I was asked to simulate a projection of this lamp onto a wall 25 feet apart. I know I need to use a Fresnel lens as a collector to achieve this, however I have many questions: 1. How should I choose the right Fresnel lens? 2. I need to...
  6. gauss44

    How do anti-reflective coatings let MORE light in through the lens?

    In the context of anti-reflective coatings put on glasses lenses, I recently read, "No light reflecting means more light in through the lens - energy must be conserved after all."? How does MORE light get in? The best I could imagine is either: 1. That by using destructive interference on...
  7. J

    Far Field lens Imaging…Does k-wave number follow arc length equation?

    If we are imaging light in the far field region. We have three situations/relations (illustrated below): Arc Length: We know the distance subtended (S) by the light ray in a lens-less system will be proportional to R (distance to the screen) and theta; simple, especially if theta is very...
  8. V

    Buy a Determinium Lens Online - What is It?

    What is a determinium lens and where I can buy it online? Thank you
  9. X

    Fourier Optics: Why Does a Lens Perform a Fourier Transform?

    I have been studying Fourier Optics and I have a basic conceptual question. I understand the mathematics of how to perform Fourier Transforms however the part of this topic I seem to have missed is why the action of a lens on light is the same as performing a Fourier Transform on the functional...
  10. I

    Finding fmax in Thin Lens Refraction Problem

    Homework Statement Hi all. This is a problem from one of the problem sheets from earlier in the term. I'm just revising for my exam tomorrow and can't solve this one. Here it is: Consider a light source placed at a fixed distance L from a screen, such that a lens of focal length f can be...
  11. L

    Image of a Convex Lens Cut in Half Horizontally

    Hello everyone, A friend of mine came up with this question in class and I really do not have a good answer. Suppose you have a convex lens that has been cut in half horizontally and the top half removed. The question is: Will the bottom half of the lens still form an image? I really...
  12. A

    Find the Focal Length Of a lens

    Homework Statement When an object is placed 69.0cm from a certain converging lens, it forms a real image. When the object is moved to 39.0cm from the lens, the image moves 19.0cm farther from the lens. Find the focal length of this lens. Homework Equations 1/do + 1/di = 1/fThe Attempt at a...
  13. A

    Optics Problem: A real object and a converging lens

    Homework Statement A real object is placed 9.00 cm from a converging lens that has a focal length of 24.0 cm. The image is________. My classmate answered "14.4 cm from the lens, virtual, and enlarged," but apparently this is incorrect. I solved it out and chose the option "14.4 cm from the...
  14. R

    What is the focal length of the lens? given magnification and distance

    Homework Statement A biology student wishes to examine a bug at a magnificaiton of +5.00 by looking through a single lens. the student wants the image of the bug to be a distance of 25cm from the lens. what is the focal length of the lens? Answer:+6.25cm Homework Equations...
  15. L

    Optics: Concentrating light with a lens

    I'm looking at concentrating light (e.g. sunlight) with a lens, and trying to figure out the maximum concentration I can get. If you have a perfectly collimated source, a lens can focus that light down to a point, but when the source has some divergence, the point you can focus down to will have...
  16. S

    How determine aspheric lens beam angle?

    Hi, I'm using an aspheric lens with a LED light source for a DIY projector. As I understand it, if I place the led light source at the focal length of the aspheric lens, the light should be collimated(parallel) coming out the other side. As I decrease the distance between the led and the...
  17. R

    Resolution for a lens from a diffraction standpoint

    Homework Statement A lens is designed to work in the visible, near-infrared, and near-ultraviolet. The best resolution of this lens from a diffraction standpoint is Options: a.) the same for all wavelengths. b.) in the near-ultraviolet. c.) indeterminate. d.) in the near-infrared. e.)...
  18. Darth Frodo

    Calculating Angular Magnification and Image Position in Compound Lens Systems

    Homework Statement 1. An object is placed 1.5m in front of a convex lens of focal length 500mm. Find the position of the image formed and state its nature. 2. A second convex lens of focal length 25mm is placed 770mm behind the first convex lens. Find the position of the final image formed and...
  19. J

    Help with optics, telecentric lens, and focusing at infinity

    Hi Guys, I have a question about a telecentric lens I've been studying and was wondering if you guys could help clear some cobwebs in my head. For starters, I am simplifying the TC lens as a compound lens. Also, this lens has 2 degrees of freedom: (1) it can be extended and retracted (2) it...
  20. C

    OPTICS: How to solve a two lens system with the object in a medium?

    Hi All, I need help determining focal length value in a two lens system. In the set up, the light source (object) is within a tube, a medium surrounds it with refractive index n1=1.52. The end of the tube is met with a curved convergent surface, the center of which is 0.635 cm away and focal...
  21. Darth Frodo

    How Do You Solve a Combination Lens Problem in Optics?

    Homework Statement An object is placed 400 mm in front of a convex lens of focal length 80 mm. Find the position of the image formed. State the nature of this image. A second concave lens of focal length 25 mm is placed 80 mm behind the first convex lens. Find the position of the final...
  22. A

    WHY does curvature of a convex lens affect focal length?

    Homework Statement For my high school physics coursework I must investigate factors affecting the focal length of a lens. I have focused on radii of curvature and completed my data collection and verified the accuracy using the lens makers equation. However, in the conclusion I am really...
  23. J

    Light problem with a mirror and a lens

    Homework Statement A +15 cm focal length lens and a flat mirror are 45 cm apart (the mirror is to the right of the lens and can be treated as a concave mirror with an infinite focus length). There is an intermediate image 30 cm to the right of the lens (15 cm to the left of the mirror) with...
  24. C

    Does a Convex Lens Cause Eye Heat When Viewing a Light Source?

    I was just wondering if a person wearing convex lenses looks at a light source... Will excess heat be generated in his eyes? As it is a converging lens.. Thanks!
  25. J

    Does Lens Thickness Affect Its Focal Length?

    Homework Statement My physics coursework hypothesis: "As the thickness of the lens increases, the focal length decreases". I tested this using a ray box, a stand to hold lenses and a screen to see where the light is most focused, which is then measured with a metre ruler. The distance 'u'...
  26. Saxby

    Lens Object Screen Problem: Finding the Focal Length and Image Distance

    Homework Statement An object is placed 2.4m from a screen, and a lens of focal length f is placed between the object and the screen so that a real image of the object is formed on the screen. When the lens is moved 1.2m toward the screen, another real image of the object is formed on the...
  27. S

    Understanding the Sign Convention for Lens Formula Proofs

    I googled for lens formula's proof on the internet and found one here http://www.tutorvista.com/content/physics/physics-ii/light-refraction/convex-lens-formula.php The problem is that during the course of derivation, it is assumed that image distance is -u following the sign convention...
  28. D

    Optic lens to collimate/focus light from a LED.

    Hello. I'm looking for a lens that can collimate (or focus far away >500mm ) a light coming out from a LED. before I give more details is this even possible? Thanks.
  29. T

    Reverse calculation of radius and principal planes of thick lens

    Dear All, I need you kind support in a problem, which I am unable to figure out. It is regarding thick lens. I am determining lens principal planes and radius using shaping factor and focal length. The forward problem I am using is, Focal length 1/f = (n-1)*[1/r1 - 1/r2...
  30. P

    Lens - What physical features makes a lens thin?

    lens -- What physical features makes a lens thin? What physical features makes a lens thin? How can you differentiate one lens from the other based on their thickness? What is the measure of their thickness?
  31. M

    Archived Optics - magnification of a converging lens

    Optics -- magnification of a converging lens Homework Statement Dioptry of converging lens is $D=3$. What is magnification ##u##? Homework Equations The Attempt at a Solution ##\frac{1}{f}=D## - dioptry. \frac{1}{f}=\frac{1}{p}+\frac{1}{l} u=\frac{l}{p} l=up...
  32. D

    Optics Problem (Curved Mirror + Lens)

    Homework Statement A convex mirror with a focal length of -20 cm is 18 cm from a convex lens whose focal length is 6.0 cm. An object is located between them, 10 cm from the mirror and 8.0 cm from the lens. The object will produce two images, one from the light which just goes through the...
  33. R

    What is the correct sign convention for the lens and mirror formula?

    So we are learning the lens formula and I have two textbooks, my school textbook and another one that is much more detailed. My school textbook gives the lens formula as:- 1/f=1/v-1/u while the other one gives 1/f=1/v+1/u (v is image distance and u is object distance) There both different! I...
  34. D

    General Lens Question: Diverging or Converging

    Homework Statement General question here: If I have a lens that looks like two concave lenses put together (I believe it is called a Meniscus), how do I conceptually tell whether the lens should be converging or diverging? I think I remember reading something saying that it depends upon which...
  35. C

    Diffraction With A Single Slit And A Lens.

    Homework Statement Trying to find the number of diffraction maxima and the width of the whole pattern. \lambda = 500nm b = 2.8μm (Slit Width) f = 100mm r = 25mm L = 25mm (Slit to Lens) Homework Equations I have the worked out the irradiance formula as: I(\theta)=I_0...
  36. R

    Why Does Light Not Refract at a Convex Lens's Optical Center?

    I'd like to know why a ray of light passing through the optical center of a convex lens does not get refracted at all. According to my knowledge, a ray of light will not get refracted if the angle of incidence is zero i.e. it is along the normal. With this in mind, I see how a ray traveling...
  37. C

    What is the Distance 'L' in the Mirror and Lens Optical System?

    Homework Statement Optical System: Biconcave lens and convex mirror separated by distance 'L'. Object placed 0.40m in front of the lens. Final image is .12m from the vertex of the mirror Lens curvature radii: 0.10m and 0.20m Mirror curvature radii: .12m Calculate the distance 'L'Homework...
  38. M

    Optics, the resulting power of the lens .?

    optics, the resulting power of the lens...?? a thin lens , made of refractive index 1.5,has a front surface +11 d power and back surface -6d ..if this lens is submerged in a liquid of refractive index 1.6, the resulting power of the lens is... a)-1 dioptre b)+1 dioptre c)-5 dioptre...
  39. H

    Focal Length of a Half Ball Lens

    Any help much appreciated - this is driving me crazy! Homework Statement Show that the focal length of a half ball lens, in air, (in the paraxial limit) is given by: f=R/n-1 Homework Equations Equation (from Hecht- Optics), for refraction at a spherical interface: nm/s0 + nl/s1...
  40. P

    Geometric Optics - Converging Lens

    Homework Statement A certain lens focuses light from an object 2.90m away as an image 46.9cm on the other side of the lens. 1. What type of lens is it? (Converging or Diverging?) 2. What is the focal length? 3. Is the image real or virtual? Homework Equations 1/di + 1/do = 1/f...
  41. J

    Diffraction from a single slit, with Lens

    Homework Statement Parallel rays of green mercury light with a wavelength of 546 nm pass through a slit covering a lens with a focal length of 60.0 cm. In the focal plane of the lens the distance from the central maximum to the first minimum is 10.2 mm. What is the width of the slit...
  42. C

    Can a single lens save the day for the broken projector?

    Homework Statement You have paid big bucks to see The Bourne Legacy at the 3-D IMAX theater in Vancouver. Just before the movie is about to begin, the theater staff tell you that the lens for the projector has just broken! You really want to see the movie and decide that it should be simple to...
  43. S

    Finding the height of an image reflected through a lens?

    Homework Statement A 2.0--tall candle flame is 2.1 m from a wall. You happen to have a lens with a focal length of 37 cm . How many places can you put the lens to form a well-focused image of the candle flame on the wall? For each location, what are the height and orientation of the...
  44. jaumzaum

    How Does Object Placement Affect Image Location in Convergent Lenses?

    I was solving the following problem, and I've got confused at the second question http://img407.imageshack.us/img407/7921/43545856.png 1) An object is put at the center of curvature C of a convergent lens. Where is the image? Calculate by gauss equation. It's obvious that the image is in...
  45. S

    How can refractive index be used to manipulate light in photonics?

    The question can be found here: http://gyazo.com/fc4d26cd35e6ce368ad2a8ed504f1dcc The refractive index it references can be found here: http://gyazo.com/94fd2f3b5ea7da9226c3acd56b0024c1 I'm not really sure where to get started on the "showing" part of the question. I anticipate that Snell's...
  46. F

    Magnification of an Image formed by a converging lens

    Homework Statement A converging lens with a focal length of 14.2 cm is used to inspect a coin. The lens forms a virtual image 30.1 cm away. What is the magnification? Homework Equations (1/Si) + (1/So) = (1/f) M = (hi/ho) = (-Si/So) The Attempt at a Solution 1/So = 1/f - 1/Si...
  47. A

    Lens Formula Confusion: Convex Lens, Cartesian Sign Conv.

    The cartesian sign convention for a convex lens is follows: 1. All distances on the principal axis are measured from the optical center. 2. The distances measured in the direction of incident rays are positive and all the distances measured in the direction opposite to that of the incident...
  48. K

    Optics - Spectacles lens Power Estimation

    Hi, I'm Chaitanya, 4th year undergraduate student in biomedical engg. I have an idea of making a mobile phone application which measures the power of your spectacle glasses. The idea is we take an image with the phone's inbuilt camera. One of the spectacle lens will be held in front of the...
  49. W

    Is a Distortion-Free Flat Lens the Future of Optics?

    http://www.sciencedaily.com/releases/2012/08/120824093523.htm If I understand the technology correctly these optical antennas substitute surface plasmon effects for the phase delays of the light passing through glass. They also use standard semiconductor manufacturing techniques meaning mass...
  50. T

    Exploring the Lens Maker Formula: Understanding Its Purpose and Significance

    Hi friends, I've a very simple doubt. The lens maker equation, why is it called lens maker equation? What is the reason behind that? thank you in advance.
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