What is Lenses: Definition and 320 Discussions

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. A

    Ray Tracing and Combination of Lenses

    I was looking at this problem. Does the problem assume that the focal point of the divergent lens is right next to it? The answer is c, saying that the focus point will be further away: but that assumes that the focal point is not RIGHT NEXT to the divergent lens. If it were RIGHT NEXT (VERY...
  2. U

    Ray diagrams, lenses and microscopes

    Hi all, I've been reading about biconvex lenses, drawing ray diagrams and real/virtual images. I'm now trying to translate this into how an image is formed in a compound infinity optics microscope. And this has raised some questions: -In an infinity optical system the object is placed at a...
  3. DataGG

    Optics - Image formation (lenses)

    Homework Statement A lense with a focal length of ##-48.0cm## forms an image ##17.0cm## to the right of the lense. Where is the object positioned? Homework Equations $$\dfrac{1}{d_0}+\dfrac{1}{d_i}=\dfrac{1}{f}$$ The Attempt at a Solution Well, since the focal length is negative, we know...
  4. T

    Lenses question -- Can lenses Magnify?

    Can lenses Magnify? i know that eyeglasses can get the image farther or nearer to fix it on the retina, but can lenses magnify as mirrors can ?
  5. J

    Relation for combination of two thick lenses

    So what if we have two thick lenses? Thanks in advance ,
  6. A

    Simple laser using magnifying glasses, lenses and a laser pointer

    Hi guys, sorry new to this, I'm looking to build a simple laser using magnifying glasses, lenses and a laser pointer. How would I go about it and can I get away with using the pointer or do I need a laser diode?
  7. E

    How Can We Determine if Someone is Farsighted?

    Homework Statement Which of the following is a characteristic of a farsighted person (nearby objects appear blurry)? a)the minimum focal length they can get for the lens of their eye is not small enough. b) the maximum focal length they can get for the lens of their eye is not large enough...
  8. P

    How to Determine Focal Length and Power of Lenses for Farsightedness

    Homework Statement A farsighted woman cannot see objects clearly that are closer to her eye than 60.0 cm. Determine the focal length and power of the spectacle lenses that will enable her to read a book at a distance of 25.0 cm. Homework Equations The equation I have been using to find...
  9. D

    Understanding Refraction and Reflection in Silvered Lenses

    When dealing with lenses which have one curved/flat surface silvered why do we consider light to refract twice before hitting the silver side? This diagram should show what i mean: The way it appears to me is that after light enters the un-silvered surface it refracts then it does...
  10. L

    Analyzing Two Converging Lenses of the Same Focal Length

    Homework Statement Two converging lenses of the same focal length f are separated by distance 2f. The axis of the second lens is inclined at angle θ = 60º with respect to the axis of the first lens. A parallel paraxial beam of light is incident from left side of the lens. Then: (A)...
  11. Racer_Rob

    Focusing laser beams with concave and convex lenses

    I'm trying to focus a 3mm diameter laser beam (527nm) to a 0.3mm spot size. According to this online calculator I need a +500mm focal length lens and a -50mm FL lens separated by 450mm. However, in practice this did not produce a focused spot. I'm assuming this calculator has made some...
  12. Y

    Difference between Aspherical Lenses types/materials

    Hi everyone, I'm building an optical system in which I need a focusing lens of a certain diameter and focal lenght. I decided to use an aspheric lens since it reduces aberrations in comparison to the spherical ones. I found many aspheric lenses with the specifications I need, nevertheless...
  13. H

    Can a converging lens become a diverging lens in liquid?

    Homework Statement (a)Can a converging lens be made to diverging if it is placed into a liquid? (b)What if?What about a converging mirror? Homework Equations Homework Equations The Attempt at a SolutionThe Attempt at a Solution (a)Let the focal length of the converging lens be...
  14. adjacent

    Understanding Focal Points: Why Textbooks Define Them Differently | Lenses Q&A

    Homework Statement I have many questions.Once I get the answer of the first one,I will proceed with the second and so on. This is really not a home work question.But... So,In my textbook as well as my teacher defines the focal point as :The point where image of a distant(Parallel rays) object...
  15. O

    Coinciding of 2F and C in ray diagram of lenses

    Hello All, Guys in my recent lecture I discussed that unlike the focal length of spherical mirrors which is half the radius of curvature, the focal length of lenses depends not only on the geometry of lenses but also on the refractive indices of the media, and that here the relation f=R/2 is...
  16. G

    Optics: Thin Lenses - Determining Focal Length

    Homework Statement In the photo (which I cannot post now, but it is a magnifying glass, and a dollar bill) the images through the lens appears twice the size and it is at a distance of 3.0cm from the lens of the magnifying glass. Determine focal length. Homework Equations 1. -di/do=m...
  17. J

    How Do You Manipulate Lenses for Optimal Image Placement?

    Homework Statement 1.Where would you place an object to obtain an image as far away from the lens as possible? 2. Suppose you have an image focused on a slide screen. You moved the image towards the lens. Which way would you move the lens to keep the image in focus? Explain Homework...
  18. M

    Optical setup: proper lenses selection

    Dear all, I am going to realize an experimental optical setup and I need your suggestions to make the correct selection of lenses. A polychromatic light beam coming from a monochromator (400-700, slit dimension: 1 mm, cone angle 11°) has to be focused onto the base of a cylindrical lens. I...
  19. V

    Two convex lenses in a system?

    What happens when you place an object into a two-lens system consisting of two convex lenses?
  20. S

    Question about reflectivity of mirrors vs transitivity of lenses

    I could not find an optics forum, so I'm posting this here. I'm trying to learn about the optics of imperfect real mirrors and prisms. I dug out my old physics book, but it just barely touches on this. 1. I read that most aluminum coated telescope mirrors reflect about 90% of the light...
  21. A

    Power of Two Lenses: Find d & l

    Homework Statement Design a thin-lens telephoto lens with a back focal distance of 50 mm and an effective focal length of 200 mm, and a maximum system length (distance between first lens and image) of 100 mm. Find the power of each of the two lenses. (Lenses are in air.)Homework Equations...
  22. C

    Optical Instruments two lenses

    Homework Statement A 2 cm tall object is 20 cm to the left of a lens with a focal length of 10 cm. A second lens with a focal length of 15 cm is 30 cm to the right of the first lens. Calculate the image position and height. Compare with ray-tracing. Homework Equations 1/f = 1/do + 1/di, m =...
  23. Zafa Pi

    Pasting polarized lenses to a PBS ?

    If a PBS (polarizing beam splitter/polarization analyzer) that emits horizontal and vertical polarized photons when observed has a horizontal polarized lens pasted over the horizontal outlet and vertical one over the vertical outlet does this change its behavior? I'm particularly concerned when...
  24. J

    How Do You Calculate Focal Length in a Two-Lens System?

    Homework Statement An object is placed at 25 cm to the left of a diverging lens. A converging lens with a focal length of 12 cm is located 30 cm to the right of the diverging lens. The two-lenses-system forms a real inverted image 17 cm to the right of the converging lens (see attachment)...
  25. A

    Total Magnification of Two Converging Lenses

    Homework Statement Two identical converging lenses have focal lengths of 15 cm and are aligned on the same principal axis. They are separated by a distance of 120 cm. An object sits a distance of 21 cm to the left of the left lens. What is the total magnification of the two lenses...
  26. A

    Converging Lens Homework: Finding Image Distance with Thin Lens Equation"

    Homework Statement An object is in front of a converging lens with a focal length of 11.0 cm. The lens produces a real image located 25.0 cm from the lens. If the lens is replaced by a new lens (in the same position) that has a focal length of 32.0 cm, what is the image distance of the...
  27. O

    Solving Optics Lens Problems: 2 Possibilities for Object Placement

    Hello, If you have an object, and a bi-convex lense, you are given the focal length, and you are given the magnification factor (M) to be 2, how are there two possibilities to place the object? One question I was doing asked this, and said: a) if the image is virtual, and M=2, find the...
  28. T

    Ray tracing through optical system of thick lenses

    Can you advise me a free software that allow to draw rays passed throught system of thick lenses (preferable in 3D)?
  29. R

    Image Formed by a System of Lenses

    Homework Statement Three converging lenses of focal length 2.5 cm are arranged with a spacing of 2.2 cm between them, and are used to image an insect 2.3 cm away. Where is the image? Homework Equations 1/do + 1/di = 1/f The Attempt at a Solution I used the above equation to find...
  30. D

    Understanding Converging Lenses: Question on Image Size

    Homework Statement This is the given question. The blue rays represent the solution. http://img16.imageshack.us/img16/7237/lenstq.jpg Homework Equations None. The Attempt at a Solution The blue rays are essentially my solutions, but only up to the point where the rays are...
  31. B

    Telescope Lenses: Focal Lengths 20cm/1cm/100cm/5cm/10cm/2cm/25cm/75cm

    Which two of the following lenses could be used to construct a telescope? Focal lengths: 20cm/1cm/100cm/5cm/10cm/2cm/25cm/75cm (a.) That magnifies 20x and has a length of approx 1.0m (b.) magnifies by 15x (c.) magnifies 50 x I used magnification=telescope focal length/eye piece...
  32. J

    Combination of spherical lenses

    Two thin lenses having focal lengths of +15 cm and -15 cm are positioned 60 cm apart. A bird stands 25 cm in front of of the converging lens. a. describe the image of the bird. Is it real or virtual? Upright or inverted? Magnified or reduced? b. If the bird is 10 cm in height, what is the...
  33. K

    Understanding ray diagrams for concave lenses

    Hey guys, So some friends and I are studying for a test and we came across this question. I've absolutely no idea what the answer is simply because every website I've found only shows parallel rays and a ray going through the centre of the lens. It's incredibly aggravating. Anyway here's the...
  34. K

    Final image distance using lenses

    A 15cm focal-length converging lens is 18cm to the right of a 4.0cm focal-length converging lens. A 4.0cm tall object is distance to the left of the first lens. For what value of is the final image of this two-lens system halfway between the two lenses? My attempt: I am working...
  35. S

    Where Can I Find Lenses for a 19th Century Peep-Show Box Project?

    Hello, I am an artist looking for advice on lenses for a project that will simulate 18th and 19th "peep-show" or "Rarekiek" boxes. See for example: http://www.loeb-larocque.com/optica.php#peep I wish to either source lenses directly or if the price is not too prohibitive, have a number of...
  36. S

    Hellowhat is the lenticular lenses?

    hello what is the lenticular lenses? thanks for the help
  37. S

    Help Geometric Objects Thin lenses Problem

    I really need help with this problem. Give me at least a hint on how to solve it. You are standing in front of a lens that projects an image of you onto a wall 2.00m on the other side of the lens. This image is three times your height. A) How far are you from the lens? B) What is...
  38. P

    Lenses and Lasers: Focal Length of 10 cm Sphere

    Homework Statement A gypsy's crystal ball can act as a thick lens whose centre thickness is twice the radius of curvature of the surface. For a 10 cm sphere of glass with n=1.5 what is the focal length? Like this? : http://postimage.org/image/niisv7bq9/ Homework Equations I am not...
  39. P

    Radius of Curvature, Lenses, Finding Di

    Homework Statement If you look at yourself in a shiny Christmas tree ball with a diameter of 8.1 cm when your face is 35. 0cm away from it, where is your image? Homework Equations 1/do + 1/di = 1/f The Attempt at a Solution 1/di = 1/4.05 cm - 1/35.0 cm di = 4.6 cm I...
  40. H

    Solving Two Lenses Problem: Ray Diagrams & Equations

    Homework Statement Extracted from NSS Physics at Work Book 3A, a textbook published by Oxford University Press. An object O is placed at distance u from the optical centre of convex lens A. The focal length of the lens is f1, where f1 > u. An image I' is formed. (b) Another convex lens B is...
  41. S

    Building a microscope with two different power lenses

    Homework Statement You've been asked to build a 14X microscope from a 2X magnifying lens and a 5X magnifying lens. What will be the tube length of your microscope? Homework Equations Meye = 25/feye Mobj = -L/fobj M = (Meye)(Mobj) The Attempt at a Solution First, are you supposed to use the...
  42. C

    Lateral Inversion of Images Formed by Convex & Concave Lenses

    Lens problem! Hi guys, When an object is placed in front of a convex lens ( not between Focus and optical centre ), the image formed on the other side should be inverted and real. My question is, with the mentioned placement of the object, will the image be laterally inverted? Further more...
  43. M

    Virtual Image Location for Negative Lens System?

    Homework Statement S is a lighted object, height=1. what is the final image that is created by the system? Homework Equations The Attempt at a Solution i just don't understand how do i find the location of a virtual image created by a negative lens when the rays converge to a...
  44. M

    Expanding Laser Beams with Focusing Lenses: Possibilities and Limitations

    I'm doing this for a home project over the summer. So let's say I took a small laser and passed the beam through some focusing lenses (or evena single lense). Is it possible for the beam to expand? Also, if the laser is powerful enough to burn through paper, will the focusing lenses be...
  45. D

    Stargazing How Do I Choose the Right Optical Lenses for Building a Telescope?

    Hi. I am new to PF. I am an incoming high schooler with an interest in astrophysics, and a friend and myself are working on building a telescope (not a very sophisticated one, just one that can reveal the craters of the moon and the satellites of Jupiter). I am curious to know if any amateur (or...
  46. A

    Lenses - magnification, position, focal length help

    Lenses - magnification, position, focal length help! ok so here is the quesiton.. An object is loacted 3.5 cm from the optical centre of a lens. The lense produces an image of magnification that is +0.667 the size of the object a) is this lens a diverging or converging lens? explain b)...
  47. J

    Multiple lenses systems - specific scenarios

    Homework Statement Hi all... this isn't really a homework question, but more a question to reinforce the concept of multiple lenses. Firstly, it makes sense that the image location of an object would be behind a 2-convergent lenses system, provided they are sufficiently spaced apart...
  48. B

    Calculating Distance and Magnification for Two Lenses | Homework Example

    Homework Statement I don't have the exact problem, but I have a sample that I made demonstrating my question: There are two lens, the first of focal length 20cm and the second of focal length 25cm. the image is located 15cm in front of the first lens, and the distance between the two lens...
  49. M

    Exploring Diameter, Aperture & Focal Length of Lenses

    I am a bit of confused with the following terms involved in the study of lenses: Diameter of lens Aperture of Lens Are these terms synonomous? And how are they related to focal length of a lens?
  50. majormaaz

    How Do You Calculate Image Distance with Multiple Lenses?

    Homework Statement Two lenses that are L = 34 cm apart are used to form an image, as shown in figure. Lens 1 is converging and has a focal length f1 = 13 cm; lens 2 is diverging and has a focal length f2 = -7.0 cm. I am supposed to find out the distance from the first mirror...
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