What is Lens: Definition and 830 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. J

    Converging lens experiment

    hi i posted the same sort of question a few times before but this time it's a little different we did an experiment with a converging lens and a candle to find an image. When the candle was placed at the focal point, which was 16.3cm, an image appeared at 136cm. I know in theory, no image...
  2. B

    Converging Lens Focusing: Finding the Optimal Lens Position

    I'm having a little problem with this question.. my brain is too small. "A converging lens has a focal length of 10 cm. A screen is placed 30 cm from an object. Where should the lens be placed, in relation to the object, to produce a focused image?" I've started with the formula 1/do +...
  3. F

    What is the magnification problem with two lenses?

    Here is the problem I am working on: Two lenses that are L = 38 cm apart are used to form an image, as shown in Figure 26-52. Lens 1 is diverging and has a focal length f1 = -7 cm; lens 2 is converging and has a focal length f2 = 16 cm. [a] Determine the distance from lens 1 to the final...
  4. N

    Solving the Biconcave Lens Problem with Reflection and Refraction

    Here's the problem: Here's what I understand: I know what a biconcave lens looks like, and how it behaves (for the most part). Of course I know that the index of refraction is ~1.00. And since the radii are equal that makes the equation somewhat easier. The thick lens equation is...
  5. B

    Measuring refractive index of liquid using lens and mirror

    hi i've got to do measure hte refractive index of a liquid with mirror and lens first of all how can i measure hte refractive index of air in this way? i don't get how i can do this, please explain :| and then for the liquid, I've been told to put the liquid over the mirror and then the...
  6. S

    Object Distance From Converging Lens for 1% Focal Length Difference

    How far away from a converging lens must an object be ( in terms of focal length, f ) so that the difference between the image distance and the focal lengh is 1% of the focal length? I tried to translate the words into an equation based on the thin lens equation but i don't know if it is...
  7. S

    Solve Thin Lens Equation: Diverging Lens, Virtual Image

    I am stuck on this problem because it been like 6 yrs since i took geometry and its due by 9 am. please help! Derive the thin lens equation: 1/object distance + 1/ image distance = 1/focal length for a divergent lens, using a diagram of a divergent lens (hint: use similar triangles)...
  8. R

    Question on light intensity at the focus of a lens.

    From using a magnifying lens under the Sun, I gather it can focus all or most of the light impinging on its surface area to a small spot and that is how it is able to create a greater intensity light at its focus (disregarding absorption in the lens.) Correct? What portion of the total light...
  9. Amith2006

    Is the Image Formed by a Concave Lens Real or Virtual?

    # A convergent beam is incident on a concave lens as shown in figure. Which of the following is not correct? a) The image formed is real b) The image formed is virtual c) The image formed is erect d) The image formed is magnified I solved it in the following way: Let f be the focal...
  10. Amith2006

    Focal length of plano convex lens

    # Diameter of a Plano-convex lens is 6 cm and the thickness at the center is 3 mm. If the speed of light in the material of the lens is 2 x 10^8 m/sec, what is the focal length of the lens? I solved it in the following way: Let R be the radius of curvature of the convex surface. Given that AB...
  11. Amith2006

    Focal length of concave lens using convex lens

    # A convex lens of focal length 10 cm forms a real image of an object placed at a distance of 20 cm from it. Midway between the convex lens and the position of the image a thin concave lens is introduced. The image formed now is at a distance of 5 cm away from the earlier position. What is the...
  12. A

    Convex Lens Image: Solve Problem & Describe Image

    I have to complete a problem about locating an image for a convex lens but I'm having trouble with it. I tried it out, but I can't complete it. Can someone help please? Locate the image for the convex lens below. Use any two rays to do so. Give the characteristics of the image. I'm having...
  13. A

    Solving Thin Lens Formula Problems

    I have to complete a chart using the thin lens forumla. Can someone please help me out? I know that the formula is 1/f= 1/do= 1/di, but I don't know how to use it. Thanks.
  14. N

    Calculating Lens Power: Q&A for Diopters

    I have a question dealing with diopters. Q: Assume that the distance from the lens of your eye to the retina is 1 inch (in effect, the image distance). Calculate the power of the lens in your eye (in diopters) for both your far point and near point. The difference between these two lens powers...
  15. C

    Minimun lens size (in meters) that will permit just resolving 2 stars

    I have really no clue on how to this:cry: please help!
  16. M

    Calculate a: Dist. b/w Lens Positions for 40 cm Object-Image Distance

    The distance between an object and its image is fixed at 40.0 cm. A converging lens of focal length f = 3.62 cm forms a sharp image for two positions of the lens. What is the distance a between these two positions? Determine: The distance between these two positions a = ____cm Could...
  17. B

    Anti-Reflecting coatings on a glass lens

    heres the question: anti-reflection coatings on a glass lens (n=1.50) consists of a magnesium fluoride (n=1.38) film, the coating thickness is chosen to eliminate any back reflectionusing the ideas of destructive interference. What is the minimum coating thickness required to eliminate the...
  18. A

    Help with light and lens problem

    Here is the problem: A converging lens with a focal length of 12.0 cm forms a virtual image 8.00 mm tall, 17.0 cm to the right of the lens. I am supposed to find the position of the object. I tried using the lens eq. 1/s + 1/s' = 1/f where s is the distance of the object from the lens, s'...
  19. J

    Optics: building a camera with quasi-hemispherical recording surface, what lens?

    I make Daguerreotypes (http://en.wikipedia.org/wiki/Daguerreotype) and I have decided that I want to move from the standard flat-plane photography and make images on silver domes instead. I have domes that are 1.85" in diameter and I want to replicate the effect that a garden gazing ball gives...
  20. T

    How do I calculate the diameter of the sun's image using two lenses in optics?

    Hi, I have an optics Q here I'm not quite sure about:- a.) An astronomers uses a single thin lens of focal length 0.5m to form a sharp image of the sun on a white screen. If the angular width of the sun is 0.5 degrees, what is the diameter of the sun's image. b.) At night the astronomer...
  21. B

    Lens problem missing one idea

    Hey guys. I have a lens problem: A lens has a power of 300 dipoters, and a radius a of 2 mm. An object is located just beyond the focal length to get high magnification. The space between the object is filled oil with an index of refraction 1.4. Estimate the resolution for 500 nm light...
  22. A

    Jupiter as a Gravitational lens?

    Jupiter as a Gravitational lens?? I remember reading in a swedish science mag about a planed probe to the solar foci 550 AU from the sun. When there it would use the gravity lensing of the sun as a telescop. But getting a probe out there and the cost of the project seems like to much of a...
  23. M

    Understanding the Lens Equation: Fish & Pattern Location

    i just need a little help with a relatively easy lens question A small fish is cast into the center of a glass sphere of radius R=5 cm and n=1.5. Where will an observer see the fish? Where will the observer see a decorative pattern painted on the back side of a sphere? So, I thought I...
  24. B

    Hyperbolic Lenses: Abberation-Free?

    Are hyperbolic lenses free of abberation?
  25. C

    Optical Lens Selection for 612nm Laser Source

    Hi, I'm trying to set up a lens system as follows: - Laser source 612nm - This passes through an apature to act as a spatial filter... - then through non-reflective glass onto a crystal of diameter upto 150um - the lens must then take the diffraction pattern from this crystal upto...
  26. W

    Normalizing Data from Lens Equation Lab

    Can anyone explain how one would normalize data from a lab? We just completed the lens equation lab in class and part of the analysis is to include "normalized" virtual object data in the graph. There are only 4 measurements taken. Any feedback would be great! :shy:
  27. N

    Digital video camera lens information

    I am going be so pleased i f anyone can suggest a website where i can find information regarding the following topic: Digital video camera lens.do anyone know a website where i can download a short video regarding fiber optics.
  28. P

    Easy way to remember imaging properties of lens?

    Is there an easy way to remember what kind of images will be formed from converging/diverging lens depending on where you place the object relative to the focus? For instance, how to tell if the image is inverted vs. erect, real vs. virtual, smaller vs. magnified? I always have a hard time...
  29. R

    More candidate cosmic string lens pairs in HUDF

    ************************************************************* http://groups.yahoo.com/group/AstroDeep/12 more candidate cosmic string lens pairs in HUDF (re comment by Levon Pogosian on astro-ph/0506400); also myriad minute bright blue sources, always on dark background mesh: Murray...
  30. russ_watters

    Stargazing New 135mm/f2.8 Lens & Rig: My Experiences So Far

    I bought a new toy to play with. It's a 135mm/f2.8 lens I found used at B&H Photo for $39. I cut a hole in the back lens cap, glued a t-thread spacer to it, and built a little piggy-back rig for it and my DSI. Its pretty heavy, so I was a little worried that my ETX wouldn't be able to handle...
  31. O

    Lens Aberrations: 1st, 3rd & 2nd Orders Explained

    I was doing some reading on lens aberrations and saw some referance to 1st and 3rd order aberrations. What are they and what is the differance? Are there and 2nd order aberrations?
  32. S

    At Center of Convex Lens & Glass Plate: What is Observed?

    A convex lens is placed on a flat glass plate and illuminated from above with monochromatic red light. When viewed from above, concentric bans of red and dark are observed. What does one observe at the exact center of the lens where the lens and the glass plate are in direct contact.
  33. D

    Solving a Physics Problem: Inverted Image & Lens Separation

    I have this Physics Problem which I am not to sure where to start it from. The problem is: A real inverted image I of an object O is formed by a certain lens. The object-image speration is d = 0.40m, measured along the central axis of the lens. The image is just half the size of the...
  34. A

    How Does Focal Length Affect the Focus Point of a Lens?

    Hi .I am reall y confused about the focal length of lens.i understand that it is the length from the lens to the point where parallel beams coming from infinity after passing through the lens cross one each other.My question ,knowing thew focal length wher exactly does it help?does it have any...
  35. vincentm

    Stargazing Upgrading Telescope Lens: Is it Possible for Meade StarQuest 60AZ-M?

    IS it possible for this one? I was given an older Meade telescope today the specs: StarQuest Model: 60AZ-M 60mm (2.4") Altazimuth refratcing telescope Lens specs: - 5x24mm viewfinder - SR4mm H12.5mm and H25mm eyepieces (0.965" barrel diameter) - 2x Barlow lenses What can i...
  36. N

    Help Solve Physics Problem Involving a Convex Lens

    Lez prob hi, An object is moving with velocity 0.01 m/s towards a convex lens of focal length 0.3m. Find the magnitude of rate of separation of image from the lens when the object is at a distance of 0.4 m from the lens. Also calculate the magnitude of the rate of change of the lateral...
  37. O

    Photographing a Bird: Solve for Camera Lens Focus

    Hi! I am having trouble with this question: You are trying to photograph a bird sitting on a tree branch, but a tall hedge is blocking your view. However, as the drawing shows, a plane mirror reflects light from the bird into your camera. If x = 4.3 m and y = 4.5 m in the drawing, for what...
  38. G

    Solution to Optics Lens Problem: Image Distance in f

    i need help! Given: A real object is located to the left of a convergent lens. The object's distance from the lens is 7/3f and its focal length is f. What is the image distance in terms of f? I tried the formula 1/f = 1/di + 1/do... it didn't work
  39. S

    Experimenting with a Diverging Lens: Discovering the Focal Point

    Hey all, I recently did an experiment using a diverging or convex lens, to produce different images according to the focal point. For the experiment I found the focal length, and set up the lens and light source at that distance. I used just paper for a screen to produce the real images created...
  40. W

    Efficiently Refract Light with a System of Lenses - Exploring Photons

    If you could set up a system of lenses so that once a steady light stream enters the system, it will be refracted within the same system permanently, what will happen to the photons? Would it take an infinite number of lenses to get the exact refraction?
  41. L

    Show Two Positions of Converging Lens for Sharp Image Formation

    A bright object is placed on one sid eof a converging lens of focal length f, and a white screen for viewing the image is on the opposite side. The distance d_T = d_i + d_0 between the object and the screen is kept fixed, but the lens can be moved. Show that if d_t > 4f , there will be two...
  42. J

    Finding Radius of Curvature for Biconvex Lens

    An object is located 36 cm to the left of a biconvex lens of index of regraction 1.5. The left surface of the lens has a radius of curvature of 20 cm. The right surface of the lens is to be shaped so that a real image will be formed 72 cm to the right of the lens. What is the required radius...
  43. E

    How Do You Calculate Lens Separation for Identical Image Size and Orientation?

    1. A coin is located 19.6cm to the left of a converging lens (f = 16.5cm). A second, identical lens is placed to the right of the first lens, such that the image formed by the combination has the same size and orientation as the original coin. Calculate the separation between the lenses...
  44. J

    Calculate Required Radius of Curvature for Biconvex Lens | Optics Problem

    An object is located 36 cm to the left of a biconvex lens of index of refraction 1.5 The left surface of the lens has a radius of curvature of 20 cm. The right surface of the lens is to be shaped so that a real image will be formed 72 cm to the right of the lens. What is the required radius...
  45. S

    Lens power/focal length question

    A friend and I are getting conflicting answers for a focal length/power question. He says he gets 22.5 diopters, whereas I get 5.1 diopters, so I was wondering who's screwing up. Here is the question and my answer: Q: If a +20 diopter lens is a symmetric double convex lens of index 1.50...
  46. russ_watters

    Stargazing New 3x Barlow lens and a 2x shorty barlow lens

    New 3x Barlow lens and a 2x "shorty" barlow lens I bought a new 3x Barlow lens and a 2x "shorty" barlow lens. I haven't done any stacking yet, but I tried the shorty and the 3x on Thursday night. It was cold and it was a work night, so I set up my telescope on my brightly-lit front porch (its...
  47. S

    Which Lens Material Requires the Most Effort to Craft?

    If you had to choose between ice(n=1.31), glass (n=1.52), or diamond(n=2.42) which would be the hardest lens to make? Which woukl be the easiest lens to make?? the one with the least radius of curvature would need the most work done on it because of the small value needed. On the other hand...
  48. K

    What Determines the Focal Length of an Einzel Lens in TOF Mass Spectrometry?

    Hi, Im working on a project in designing a (TOF) mass spectrometer and want to include an einzel lens in order to help focus the ion beam onto the detector. I know the basics behind the operation of the lens, but am struggling to find any equations for the focal length of an einzel lens...
  49. S

    Understanding Light Refraction Through Lens Experiments

    One of our lab assignments was to use a lens to focus an arrow-shaped beam of light onto a sheet of paper. We were then told to predict what would happen if we covered up the top/bottom/left/right half of the lens. I predicted that covering the top portion would cause the bottom part of the...
  50. maverick280857

    What is the correct number of refractions for silvered lenses?

    Hello I've been reading optics (both the cartesian and real/virtual sign convention) and I have some queries: 1. I was trying to work out problems involving silvered lenses (spherical lens with one side silvered) and first I tried to reason to myself how the imaging would take place. This...
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