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. Y

    Find the total magnification for a system of 2 converging lenses

    Homework Statement There are two converging lenses. The object of the first lens (i.e. the lens on the left) is 17.5 cm to the left of the first lens, and the resulting image from the first lens is 23.33 cm to the right of the first lens. The second lens is 40 cm to the right of the first...
  2. S

    What Is the Focal Length and Magnification in Multi-Lens Systems?

    Homework Statement 1) I have five lenses with f=25 placed at distance 50 from each other, what is the focal length of this system? 2) A light source is placed in the focal point of a lens with f=50, at d=600 a lens with f=400 is placed, at the focal point of the second lens the image is...
  3. D

    Ball Lenses Concept Explained: Get Answers Here

    I like to know some concept about ball lenses (spherical lenses) specially when they are in contact with each other. I googled it but nothing. I will really be thankful if anyone can help me.
  4. L

    Graph Plotting: Determine u & v When Given 1/u & 1/v

    Plot a graph of 1/u against 1/v and find the intercept on the 1/u axis. Determine from your graph a) the value of u, when v= 27cm b) the value of v,when u 27cm I'm sorry but I don't really understand how to find 27cm on my graph when there's nothing like that on it.
  5. N

    What is the relationship between numerical aperture and focal length in lenses?

    Hi I have two general questions regarding a lens and its numerical aperture: 1) From this picture http://en.wikipedia.org/wiki/File:Numerical_aperture_for_a_lens.svg (from the Wiki-article http://en.wikipedia.org/wiki/Numerical_aperture) it seems to me that there is a propotionality between...
  6. E

    Optics of lenses and mirrors question:

    So I was going through the playlist of videos here, and have understood everything so far. However, they are going through this question and he introduces this chart, so the student can use it as a reference to know if he got the answer correct...
  7. C

    Mirrors reflect and lenses refract-can someone verify if I understand it?

    Mirrors reflect and lenses refract-can someone verify if I understand it?
  8. G

    Near and far points with contact lenses

    Homework Statement A nearsighted person has near and far points of 11.0 and 22.0 cm , respectively. If she puts on contact lenses with power P = -4.00 D, what are her new near and far points? Homework Equations P=1/f 1/f=1/do+1/di where f=focal point, do=distance to object...
  9. W

    Why is the image distance negative in a Two Thin Lens setup?

    1. Two 25.0 cm focal length converging lenses are placed 16.5 cm apart. An object is placed 35.0 cm in front of one lens. Where will the final image formed by the second lens be located? I got the right answer but I'm not sure why the image distance is negative when the image (formed by the...
  10. fsonnichsen

    Comparing GRIN Lenses vs Convex for Laser Beam Collimation

    I am interested in comparing the effectiveness of GRIN lenses vs aspheric-convex ones for collimating laser beams. I can imagine some practical advantages however I would be interested in any information comparing the advantage of one method over the other from an optical standpoint. Thanks...
  11. R

    Effective Focal Length of Multiple Lenses

    In my Optics book (Hecht, 4th edition) the author discusses how, when dealing with a multiple lens system (say, with n many lenses), one can think of the system as a single lens system, with an effective focal length given by: 1/f(effective) = 1/f1 + 1/f2 + ... + 1/fn My question is this...
  12. L

    What is the focal length of the second lens in an afocal system?

    Homework Statement An object at a distance a1 in front of a convex lens with the focal length f1 is imaged at a distance b1. A second lens at the distance d from the first lens with the focal length f2 is then imaging this Image with the image distance b2. a) Give the image distance b1 as...
  13. Y

    CPC and Fresnel Lenses for Solar Cell Power

    I want to maximize solar cell efficiency regardless of the sun's angle and so I've been looking at placing Compound Parabolic Concentrator (CPC) over the top of a high efficiency round solar cell. If I come up with a good design then I would like to try and manufacture some of them to see if I...
  14. F

    What should be a very simple optics question is giving me problems (two lenses)

    I'm studying for the GREs, and I ran across this problem: Object located at x=0 Lens 1 located at x=40cm Lens 2 located at x=70cm (30cm from lens 1) f1 = 20cm f2 = 10cm Both lenses are converging, thin lenses. So I have to find the final image location. The understanding I have of multiple...
  15. X

    Optics - Two lenses touching each other with oil inbetween

    Homework Statement Two identical, thin, plano-convex lenses with radii of curvature of 15 cm are situated with their curved surfaces in contact at their centers. The intervening space is filled with oil of refractive index 1.65. The index of the glass is 1.50. Determine the focal length of...
  16. D

    Corrective lenses, power of the eye change

    Ok so I'm doing my physics assignment on optics and have come to a point where i seriously need help. I need to talk about how a corrective lens, in particular contact lens, changes the optical power of the eye to suit different refractive errors. I need to know how a contact lens changes...
  17. P

    Diffraction and Aperture Size: How Does It Affect Image Resolution?

    Hi there, I understand somewhat how diffraction works in terms of the aperture of a camera lens and the resulting loss in resolution in the image, but my question is: Is the degree of diffraction only dependent upon absolute aperture size, or the size of the entrance pupil? For example, f/22...
  18. F

    Exploring the Relationship Between Convex Lenses and Objects

    Homework Statement I did an experiment with a convex lens, object, and image. As the lens moved farther and farther away from the object, the image decreased its distance (to remain in focus) from the object as well up to a certain point. After that point, as the lens increased its distance...
  19. F

    Does Focal Length Differ for Convex Lenses?

    I know that for concave lenses, the focal length is one half the length of the radius of the circle. Is this also true for convex lenses? Thanks
  20. I

    Can spherical aberration be avoided in lenses with non-spherical curves?

    I've been doing some calculations on lenses, and I'm a little confused about some of the diagrams I've seen. Looking at a ray diagrams, I see the light passing through the lens, at one angle, and then converging on a focal point from there. Using snells law to calculate refraction through the...
  21. R

    Revising simple lenses - magnified, and diminished images

    Basically, I'm trying to revise lenses and the one thing I never really understood was how to tell whether an image is magnified or diminished. http://store.aqa.org.uk/qual/gce/pdf/AQA-2450-W-TRB-OGA.PDF pages 6 and 7 has the diagrams to show what I mean I can do the geometry of an object...
  22. zimo

    Two lenses problem, multiple interpretations, no true answer

    Homework Statement Two lenses, with 20cm focals are in 1m distance from each other. A body is located 60cm from the right lens.Homework Equations I figured that the relevant equation should be: \frac{n1}{u} + \frac{n2}{v} = \frac{n2 - n1}{r} but perhaps a I'm wrong. The Attempt at a Solution...
  23. A

    What is the size of the image of a tree on a man's retina?

    Homework Statement A man looks at a tree of height 20.0m a distance of 300m away. the cornea has a radius of curvature of 7.7mm, eye has refractive index of 1.47 and the length of the eye is 24.0mm. Calculate the size of the image of the tree on the man's retina. Homework Equations...
  24. A

    Physics:series of 3 lenses calculate mag

    Homework Statement An object is placed 10.0 cm from a series of 3 lenses. The first lens has focal length of 5.00 cm, the second lens has a focal length of 9.00 cm and the final lens has a focal length of 3.00 cm. the distance between each lens is 25.0 cm. Find the final position of the image...
  25. Z

    In the following figure, the space b/w the glass lenses is filled with

    In the following figure, the space b/w the glass lenses is filled with water. We have to find the focal length of the system (radii of curvature, refractive indices given) http://203.196.176.41/VLEBT_RootRepository/Resources/6c32207c-7c5a-4462-b90c-89b0c196bc72.gif Now to calculate the...
  26. E

    Any tutorial on optic physics using 2 lenses (+ and -)

    the title pretty much. thanks.
  27. K

    How Do You Calculate Image Position with Two Converging Lenses?

    Homework Statement Two converging lenses, each of focal length 14.7 cm, are placed 39.7 cm apart, and an object is placed 29.3 cm in front of the first. How far from the first lens is the final image formed? What is the magnification of the system? Answer in units of cm. Homework...
  28. S

    Understanding Lens Experiment Results: Focal Length and Graph Interpretation

    Well at school we are doing an experiment to find out the factors which affect the distance between the lens and the image. Well I did the convex lens experiement and from my results i plotted a graph which is y vs x The distance between the lightbulb and lens is x and the distance between...
  29. A

    System focal length for thin lenses

    Homework Statement Three “thin” lenses, each with focal length 25 mm, are placed 5 cm from each other. What is system focal length? Homework Equations Lens equation: (1/oxd) + (1/ixd) = i/fx Oxd = object distance Ixd = image distance fx = focal The Attempt at a Solution...
  30. B

    Increasing Laser Tag Gun Range with Convex Lenses?

    So this is the case - I've bought some shocking laser tag guns to play with my friends, though I am unsatisfied with their range which is merely 5 meters. I was wondering if I could add some convex lenses in front of the laser gun in order to increase the range of the laser, would that work...
  31. C

    Understanding Virtual Objects and Negative Do Values in Lenses

    I would appreciate some clarification on working with lenses and virtual objects (when the object distance do is negative). I'm not sure what happens when the do is negative and you get a positive value for di. On which side of the lens does the image go? Normally, for a lens, if di is...
  32. L

    Thin Lenses: Understanding (3/2)f in Image Formation

    Homework Statement An object is 3 times further from a a lens than its focal length. Let f rep focal length. How man times the focal length of the lens is the image from the lense? The answer is (3/2)f but I don't understand why. Could someone please explain it to me?
  33. edpell

    The Longest Focal Length for Lenses & Mirrors

    What is the longest focal length practical for a lens and/or shaped mirror? I ask because it would be good if we could put a mirror at GEO and shine sunlight at one spot on the Earth 24 hours per day for energy production. The problem is sunlight is dispersing 1% so from 36,000km it would...
  34. P

    Mirrors & Lenses: Understanding Virtual and Real Images

    Homework Statement True or False 1. A single diverging lens can only make a virtual image. 2. When parallel rays strike a concave spherical mirror with radius R they are focussed through a point R from the mirror. 3. An object placed at distance greater than the focal length of a...
  35. M

    Convex Lenses: Determining Real/Virtual Images

    Homework Statement Two thin convex lenses (1 and 2) and a small object are arranged as shown. a) Use the three principal rays to determine the location of the image of the object produced by lens 1. . Object --------.F1---0(Thin lens 1)---.F1-----------.F2----0(Thin lens 2 -...
  36. D

    Convergent Lenses: 2-Part Problem and Solution | Focal Point and Image Location

    Homework Statement This is a 2 part problem but I figure out the first part. Heres the 1st problem and the solution: 7- Given a convergent lens which has a focal point f. An object is placed at distance p = \frac{4}{3}f to the left of the lens. See the sketch. Solution: q1 = 4f, and is a...
  37. R

    Thick Lens Image Size: Equation & Calculation

    which equation can be used to know the image size formed by a thick lens e.g. I want to know the height of the image formed of an object 0.03 cm high. Which equation can be used
  38. D

    Ray diagrams (lenses) problem. I need full explanations.

    Ray diagrams (lenses) urgent problem. I need full explanations. 1. The question An object of height 2cm is placed 15 cm from a thin converging lens of focal length 10cm. Complete the paths of two rays on the figure to show their passage through the lens to the image formed. 2. The...
  39. P

    Harnessing Solar Energy with Fresnel Lenses

    i am about to do a project on harnessing solar energy using fresnel lens. However, i do not understand how a fresnel lens works. Could someone please clarify how it works (how can it converge light despite having a flat face) and why does it have more converging ability than other lenses?
  40. W

    Quality of Lenses Using Newton's rings

    Homework Statement Basically I'm writing up a formal report on our experiment on Newton's rings - one of the things in our aims was in investigate the quality of the lenses we were using. Whilst many sites also say Newton's rings can be used to investigate the quality of the lenses not much...
  41. G

    A question concerning lenses and the resulting images

    Imagine a situation where an object is placed infinitely far away from a convex, converging lens such that the light rays that come from the object are parallel to the principal axis. The real image forms at the focal point. In this situation, the magnification is 0, so if a screen was placed at...
  42. J

    Optics - working with multiple lenses.

    I have never used this template, but I will do my best. THe main problem involves assumption. My teacher isn't sure how to help with this. I thought that there might be some Optics experts here that could point me in the correct direction. Homework Statement I have been asked to do some...
  43. C

    Exploring the Difference in Focal Lengths of Telephoto & Convex Lenses

    Why is a telephoto lens considered to have a longer focal length than that of single convex lens?
  44. K

    Fresh water and contact lenses

    I kitesurf a lot in both fresh water and salt water. I wear well-fitting contact lenses that do not shift around or come out, even if I rub my eyes. In SALT WATER: I can crater from 20 feet in the air with a thunderous crash and get dragged through and tumbled by waves with my eyes open...
  45. G

    Where to buy cheap plastic lenses?

    Hi, does anyone know where to buy cheap plastic lenses online? I need lenses of 0.8-1.2mm diameter and 5-50mm F.L. Thanks
  46. P

    Lenses- magnification adn focal length

    Homework Statement Hey,, I was wondering if anyone could help me with some physics work i am doing as i am completely stuck. Is there supposed to be any relationship with the magnification and focal length of lenses and if so what is it? I did an experiment and measure the magnification of...
  47. Z

    Optical System: Two Identical Lenses w/2fo Focal Length

    Homework Statement An optical system consists of two identical lenses; the focal length of each lens is fo (where fo) is positive). The lenses are separted by a distance d. Denote the focal lenths of the lens assembly by f and f'. a) Show that for any separation of the lenses f = f'...
  48. B

    Why Do Diverging Lenses Always Produce Shrunken Images?

    I noticed that for converging devices the size and orientation of the image formed depends on whether the object is located inside or outside the focal point and center of curvature. I also read that no matter where the object is with respect to a diverging lense the image formed will always be...
  49. C

    How Does Light Behave When Emitted From a Focal Point Through a Convex Lens?

    Homework Statement 1. A small bulb is placed in front of a convex lens. It is placed at one focal point of the lens. Draw at least five rays from the bulb that pass through the lens. Where is the lens located in this case? Explain. (Hint: How are the rays that have passed through the...
  50. A

    Solve Relativistic Lens Problem: Focal Length & Gamma

    How would you go about solving a problem involving a lens moving at relativistic speeds, or an object being relativistic being viewed through a lens? instead of coming up with a specific problem, does anyone know what happens to lens' focal length and such as its velocity becomes large? not so...
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