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. W

    I need some help with this project (optics and lens design)

    The diagram below is not to scale. I'm trying to add a lens (or lenses) behind the one shown in this camera so that I can focus the image on a film plane of 15mm, rather than the current 120mm (Y). The focal length (X) needs to be at or greater than the current 60mm. What would the...
  2. M

    Calculating Lens Position for Photographing Objects at Different Distances

    [b]1. A 70 mm focal-length lens is used to focus an image on the film of a camera. The maximum distance allowed between the lens and the film plane is 120 mm. How far ahead of the film should the lens be if the object to be photographed is at the following distance from the lens?When it is 13.2m...
  3. G

    Difference between focal length and the distance from the lens

    Lens and distances I do use images as help when working theses out. going to try and scan theses in but tryed my best just using pc for now. 0 = lens F = focal length 1) a camera with a 50mm focal length lens is focused on a persons face 1m from the lense. show that the film will be about...
  4. F

    Question about a Carl Zeiss lens

    Ok so this really has nothing to do with astronomy, besides the use of lens,... but it is a lens question so here goes :P (moderators may move this if their's a more appropriate place for it) Information printed on the lens: "Carl Zeiss Tessar 2.0/3.7 2MP Autofocus". This is from a...
  5. S

    Issues with Simple Glass Lens & White Light

    Homework Statement A simple glass lens do not focus the image of an object correctly under white light because a. the lens absorbs light b. the glass has come colouration due to impurities c. the surface of the lens reflect some light d. a glass prism splits sunlight into different...
  6. L

    Why Is My Calculation of Lens Object Distance Incorrect?

    1.An object is placed to the left of a lens, and a real image is formed to the right of the lens. The image is inverted relative to the object and is one-half the size of the object. The distance between the object and the image is 102.0 cm. (a1) How far from the lens is the object...
  7. 0

    Getting Started with Lens Design

    please suggest some good references for lens design. i wish to start from scratch.. i am a complete amateur in this field.
  8. M

    Are Students Required to Attempt Homework Before Receiving Help in Physics?

  9. J

    Solving Lens Makers Formula: Image Location @ 500cm o, f=50cm

    Homework Statement A concave mirror has a focal length of f=50 cm. If an object is at o=500cm, where is the image? Homework Equations 1/f = 1/o + 1/i The Attempt at a Solution 1/50 = 1/500 + 1/55.56 What I don't understand is "where is the image"? How do I interpret it from...
  10. M

    Optic question about a positive-meniscus lens

    i was asked to find the angle \theta, the height h2, and the back focal length in terms of the radius of curvatures. I'm really stunned that i couldn't draw a line. thanks in advance. http://img94.imageshack.us/img94/8336/lens.png
  11. G

    Thin lens and Image Location

    Homework Statement A small fish, four feet below the surface of Lake Lansing is viewed through a simple thin converging lens with focal length 30 feet. If the lens is 2 feet above the water surface, where is the image of the fish seen by the observer? Assume the fish lies on the optical axis...
  12. G

    Glass Lens affects Magnetic Fields?

    Hello all, doing some reasoning and subsequent Gadenkin experiments, followed by a Non-scientific experiment results in some interesting changes in magnetic fields using glass lenses. Here it is, and please help me to explain this phenomenon, as I can find no mention of it anywhere. Two bar...
  13. D

    How Can You Tell if Your Glasses Have High-Index Lenses?

    Recently, I purchased a pair of glasses from a privately owned optic store. I specifically asked for hi-index lens (1.56 or 1.60, I am not sure). The lens I got, however, is kind of thick (around 5 mm thick on the edges).My eye -sight is poor though, -5.00 sphere, -1.25 cylinder on the worst...
  14. M

    Optics - Defining front and back of lens

    Working on some optics problems and I am confused about the front and back of the lens. The sign conventions are key to finding the correct image location. Now, is the front always where the object is located? The problem I am working on involves a divergent lens and a concave mirror. The...
  15. S

    Combining Lenses and Mirrors: Finding the Focal Length and Image Formation

    Homework Statement Question B only Homework Equations The Attempt at a Solution 1) Why we use f=15.0cm? Shouldn't it be f=infinity considering plane mirror have an infinity focal length? 2) Normally I do combination(lens, mirrors), firstly I will consider the front...
  16. DaveC426913

    How can I fix thisHow can I eliminate lens distortion in surveying photography?

    Photography/optical lens distortion/surveying. Please move to appropriate forum. I wish to survey an area of a friend's backyard using overhead photos. I can get photos from about 25 feet up a TV antenna with a digital SLR that has a 14-42mm lens. The area to be surveyed is 70'x20' and is...
  17. S

    What is the distance between a diverging lens and a filament?

    Homework Statement A diverging lens with focus 5 cm is placed on a filament. Find the distance between the lens and the filamentHomework Equations \frac{1}{f}=\frac{1}{di}+\frac{1}{d}The Attempt at a Solution Focus of diverging lens is negative so, f = -5 cm. I think the question is asking...
  18. N

    How to understand the image of lens at infinity

    An object at the focal length distance from the lens is imaged at infinity,Do this mean that under this situation, our eyes could not see the image? but as our eyes could see the stars from infinity, do this mean that the image of lens which is discussed above is just viewed through screen ,and...
  19. N

    Calculating Focal Length of a Converging Lens Using Incident and Refracted Rays

    Homework Statement The figure illustrates qualitatively a converging lens focusing monochromatic rays from A to B. The vertical and horizontal scales of the figure are not the same. The top ray leaves A at an angle of 2.38 deg above the optic axis and leaves B at an angle of 1.25 deg below the...
  20. O

    Interference and Diffraction: Coating on a Lens to Minimize Reflection

    Homework Statement What is the minimum thickness of coating which should be placed on a lens in order to minimize reflection of 661 nm light? The index of refraction of the coating material is 1.40 and the index of the glass is 1.65. Hint: You must take into account the 180 degree...
  21. 0

    Can I Use a 2/3" CCTV Lens on a 1/3" Camera?

    i have a camera with 1/3 " format. I have a cctv lens in front of it with a focal length of 50mm. In order to improve my FOV i intend to use a cctv lens of a smaller focal length, and the vendor is providing me a smaller focal length for a 2/3 " format. i want to know if a cctv of say 25mm...
  22. J

    Angular Magnification for mirrors and lens

    Homework Statement I'm looking for someone to clarify a strange result regarding angular magnification. For both mirrors and lens. Homework Equations m(angular) = θ'/θ M(lateral) = h'/h = - d'/d θ ≈ h/d (for small angles) The Attempt at a Solution Using the angle equation, I get a...
  23. J

    Solving Lens Image Problem: Where is Image Formed?

    An object 1.95 cm high is placed 11.2 cm in front of a convex mirror with a radius of curvature of 9.8 cm. Where is the image formed?? So i know Di= (Doxf)/(Do+f)...(11.2 x 9.8)/ (11.2 + 9.8) = 5.23 cm However, the correct answer is 3.41 cm What am i doing wrong here? I know that the...
  24. O

    Optical Instruments I - Thin Lens

    Homework Statement part1: In the Figure below a lens of focal length 8 cm is placed between a plane mirror and a pin hole. The other side of the pin hole is illuminated by a light source (not shown), so that the light passes through the hole and is then collected by the lens. If the pin hole...
  25. P

    Near & Far Point of Eye: Power of Lens & Max Distance

    the near point and far point of an eye are 35cm and 300cm respectively.what is power of lens so that the person can see objects at 25cm .with this lens what is the maximum distance he can see. f=xd/x-d p=1/f in m i could only solve the first part of the problem.p=1.14d...
  26. M

    Serveral Lens generate image

    Good afternoon, I want to check another problem about optical physics: There are taken N equal converging lens, ordered one by one in a distance of f, where f is the focal distance. There is an object standing in a distance of 0,5*f of the first lens. A Sketch...
  27. K

    Difference between plano-convex and biconvex lens

    Hi all, I am implementing a lab activity for a 2 lens set-up that will serve as a simple telescope. In the teacher's manual, it lists down 2 plano-convex lenses, with the 2 curved surfaces facing each other. The plane faces will respectively face the light source and the observer's eye...
  28. M

    Potential temperature of a fresnel lens focal point

    Hi, I have a fresnel lens from a old big screen tv and it is roughly 1 meter square. The focal point comes down to roughly 2.5cm square (1"). On a sunny day in Hawaii I can melt copper wire after about a minute. Copper has a melting point of 1083°C (1981.4 °F) . That's some serious fun! I...
  29. C

    Optics: Thin Lens and Image Formation

    Homework Statement A student is working in an optics lab and has a light bulb which is 100 cm from a screen. She needs to make a real image a real image of the bulb on the screen and she has a converging lens with a focal length of +15 cm. Find two places she can put the lens and give object...
  30. J

    Why can we see the image produced by a converging lens?

    Homework Statement Diverging lenses produce a "virtual" image, which can be seen but can't be projected, and converging lenses produce a "real" image which can be projected but not seen. How come we can see the image produced by a converging lens, which is supposed to be a real image...
  31. W

    Focal Length of Converging Lens: 10.03 cm

    1. When an object 5.0 cm tall is placed 12 cm from a converging lens, an image is formed on the same side of the lens as the object but the image is 61 cm away from the lens. What is the focal length of the lens? 2. 1/f = 1/do + 1/di 3. 1/f = 1/do + 1/di = 1/12 + 1/61...
  32. W

    Calculating Focal Length of a Converging Lens Using Object and Image Distances

    Lens -- find the focal length 1. An object 3.0 cm tall is placed 20 cm in front of a converging lens. A real image is formed 10 cm from the lens. What is the focal length of the lens? 2. 1/f = 1/do + 1/di 3. 1/f = 1/do + 1/di 1/f = 1/20 + 1/10 f = 6.667 cm...
  33. W

    Mirrors (concave) + questions on lens and mirrors

    1. The image of the moon is formed by a concave mirror whose radius of curvature is 4.20 m at a time when the moon's distance is 3.8 x 10^5 km. What is the diameter of the image of the moon if the diameter of the moon is 3480 km? 2. 1/f = 1/do + 1/di M = hi/ho = - di/do 3...
  34. S

    A Few Question On Lens and Magnification

    Homework Statement So i thought it was Real, magnified, and inverted but just wanted to check. Then also i wanted to know this here is the picture http://www.gatewaytosedona.com/image/articles4/2121/EST_Jupiter_416w.jpg Look up the size of Jupiter and the distance to Jupiter when it...
  35. E

    Elementary Corrective Lens Problem

    Homework Statement A farsighted woman breaks her current eyeglasses and is using an old pair whose refractive power is 1.655 diopters. Since these eyeglasses do not completely correct her vision, she must hold a newspaper 39.4 cm from her eyes in order to read it. She wears the eyeglasses...
  36. H

    Calculating Object Distance from Lens with Magnification and Focal Length

    Homework Statement An object is in front of a lens with a focal length of -15cm. An image ½ the side of the object is formed. How far is the object from the lens?Homework Equations m - magnification q - distance from image p - distance from object f - focal length m = -q/p 1/p + 1/q = 1/fThe...
  37. 0

    Beam emergence from cylindrical lens

    if a cylindrical lens is put in the path of a laser beam what is expected to be seen at its focal plane? how will the beam look like after emerging from it?
  38. C

    Lens can focus the light to a smaller spot by ?

    Lens can focus the light to a smaller spot by ...?? I learn that increase of the beam size of the laser before coupling it to the fiber can increase the coupling efficiency of it. Can I know why is this so? Maybe the fiber is of very small diameter, and the focal lens in front of the...
  39. K

    Intensity of a laser through a converging lens

    Homework Statement A laser beam passes through a converging lens with a focal length of 19cm. At what distance past the lens has the laser beam's intensity increased by a factor of 6? Homework Equations I=\frac{c\epsilon_0 E_0^2}{2} ?? The Attempt at a Solution To be honest, I'm...
  40. K

    What is the focal length of the lens?

    Homework Statement When a diverging lens is held 12 cm above a line of print, as in Figure 26.29, the image is 4.1 cm beneath the lens. What is the focal length of the lens? Homework Equations 1/di + 1/do = 1/f The Attempt at a Solution 1/di + 1/do = 1/f 1/4.1 + 1/12 = 1/f f =...
  41. I

    Focal Length and Lens Thickness: Exploring the Relationship

    Hi All! Im a bit confused regarding the relationship between focal length and the thickness of a lense. In the lab that we performed, my data seems to be skewed and I am unable to decipher the trend. Can someone explainwhat happens to the focal length as the thickness of the lenses...
  42. P

    Determine image distance relative to lens

    Homework Statement Two identical diverging lenses are separated by 13 cm. The focal length of each lens is -6.5 cm. An object is located 3.0 cm to the left of the lens that is on the left. Determine the final image distance relative to the lens on the right. Homework Equations 1/i + 1/o...
  43. 0

    Understand Cylindrical Lens Imaging & Refs

    can anyone help me in understanding the concept of a cylindrical lens ? how is the imaging by a cylindrical lens different from that of a sphericaL lens? how does one decide to use a particular lens or a system of lenses for image formation? please suggest some good reference for this .. thanx
  44. K

    Smallest distance between object and image - lens.

    Homework Statement Find the smallest distance between the object and a real image, when the focal distance of the lens is f Homework Equations \frac{1}{s}+ \frac{1}{p} = \frac{1}{f}, where s is the distance of the object from the lens and p is the distance of the image. The Attempt at a...
  45. Y

    Focusing gaussian beam using a lens

    I am studying further about Gaussian optics. When Gaussian beam pass through a lens, the waist location is given by (z'-f) = (z-f)M^2 Where, z' is the waist location after lens, z is waist location before lens, f is the focal length of the lens M is the magnification. In Gaussian...
  46. 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...
  47. 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...
  48. 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...
  49. 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...
  50. 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...
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