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. N

    Solving Two Lens System: O1, F1, F2, i2, M

    Homework Statement Two Lens systems: Lens one is a diverging lens and lens two is converging O1 (object distance) = 9.6 cm Focal length F1= 6.5 cm distance between the two lenses is 13 cm F2 = 7.4 cm Find the image distance i2 for the image produced by lens 2 (the final image...
  2. T

    Lens questions from a software engineer

    Hello everyone, I am a software engineer and know very little about lenses but am trying to learn. I am confused about the differences between convex-convex and plano-convex and how to decide how to design an actual plastic lens for a real world application. Here is an example (not real...
  3. K

    Lens and Mirrors: Which Diagram Has the Larger Image?

    Homework Statement Which of the following diagrams involves a larger image? Homework Equations The Attempt at a Solution I believe its the image with the mirror.
  4. A

    Converging lens becomes Diverging lens

    Homework Statement Can a converging lens in air become a diverging lens in a different refractive medium? Homework Equations n1sin(θ1)=n2sin(θ2) The Attempt at a Solution I was thinking that it would not matter what medium the lens was in, as light would still hit the lens the...
  5. Z

    How Do You Calculate Image Distance and Magnification for a Camera Lens?

    Homework Statement Was wondering if someone could help... Homework Equations 1/f = 1/u + 1/v m = v/u The Attempt at a Solution Using: 1/f = 1/u + 1/v 1/50 = 1/8000 + 1/(v) v = 50.3 mm Then to calculate the linear magnification of the image, using m = v/u with same v and u...
  6. N

    Calculating EFL of a Three Lens System

    If I have three lenses, each one 50 mm in diameter and with focal lengths of 500mm, -125mm and 150 mm, What would be the EFL if I combined them all together (assuming zero distance between them). I have been looking online for focal lengths of three lens systems but cannot find anything...
  7. Z

    Simple Lens Diagram for a Camera

    Homework Statement A simple camera has a converging lens and the image is in focus on the screen. The paths of three rays from the tree to the lens are shown in the attached diagram. Complete these paths to show the formation of the image on the film.Homework Equations The Attempt at a...
  8. Z

    Question from simple lens diagram (camera)

    Homework Statement A simple camera has a converging lens of focal length 50.0 mm. It is used to photograph a tree 3.00 m high. The tree is 8.00 m away from the lens. Calculate the distance v between the lens and the film, giving your answer in mm to three significant figures...
  9. J

    Can a Magnetic Lens Have Multiple Focal Points?

    Hello, I wanted to ask, is it possible for a magnetic lens to have many focal points, when the magnetic field of the lens is sufficiently large? if so what is the reason for this? how does this give better resolution of images compared to a simple optical lens. I know for a normal optical lens...
  10. S

    Focal Length of Lens: Solving for f with Object and Image Distances

    The homework problem is "An object 26.0 cm in front of a certain lens is imaged 1.60 cm in front of that lens (on the same side as the object). What is the focal length (in centimeters) of this lens" 1/f = 1/di + 1/do I tried solving based on having distance of object (do) and...
  11. S

    Why Was My Calculation of a -4.2 Diopter Lens's Focal Length Rejected?

    The problem reads "What is the focal length (in meters) of a -4.2 diopter lens" The formula equation I have is = 1/f to get the diopter power -4.2 = 1/f and solve for f I get -.2381 This is a homework problem where the solutions are entered on line. I entered the solution above...
  12. M

    What Is the Focal Length of a Flat Glass Lens?

    What is the focal length of a thin, flat piece of glass with no curvature? I found that the power is 0 diopters, but I don't know what the focal length is.
  13. T

    How Does Lens Focal Length Affect Image Size?

    Homework Statement An object is located 26.0cm from a certain lens. The lens forms a real image that is twice as high as the object. (i) What is the focal length of this lens? (ii) Now replace the lens used in Part 1 with another lens. The new lens is a diverging lens whose focal...
  14. R

    Diverging lens, calculating image location

    Homework Statement Diverging lens with focus of 2 meters. The object is 3.66 meters away from the lens. Find the exact image location. Homework Equations 1/object + 1/image = 1/f The Attempt at a Solution I plugged in the numbers with a negative value for the focal length but I...
  15. S

    Fisheye Lens (alt/az) to Flat (RA/Dec)?

    I have a fisheye lens which sees 180 degrees of the sky. It registers the entire sky on a 640x480 grid of pixels. Let's assume I know where the zenith and north are on the plate. That allows me to find the alt/az of every pixel in the circular image. The fisheye is linear in the distance from...
  16. Z

    Spectacles, Focal length and Lens Formula

    Homework Statement When using the lens formula: 1/f = 1/u + 1/v for someone who has short sightedness and cannot focus on objects on objects more than 2.5m away, I get: 1/f = 1/infinity + 1/-2.5 f = -2.5 mIf using the formula for someone who had long sightedness and could not focus on...
  17. Who Am I

    I got a Zhumell Z8 Dobsonian. The stock lens is decent

    I got a Zhumell Z8 Dobsonian. The stock lens is decent, I think. One is a 68 degree Plossl and the other is a zoomed in Plossl that I don't know as much about. I want a new lens so I can get better views. I am mostly interested in deep sky objects, seeing as there are only a handful of...
  18. fluidistic

    Plano-concave thin lens, checking my result

    Homework Statement Determine the focal length of a plano-concave lens (n=1.5) which has a radius of curvature of 10 cm. What is its power in diopters? Homework Equations None given. The Attempt at a Solution 1/f=(n-1)(1/R_1-1/R_2)=(1/2)(-0.1)=-1/20. Thus f=5 cm and P=-20 m^(-1)...
  19. fluidistic

    Describing Image of a Bi-Concave Lens with n=1.5

    Homework Statement A bi-concave lens (n=1.5) has radii of 20 cm and 10cm and a thickness of 5 cm. Describe the image of an object of 2.5 cm of hight and situated at 8 cm from the first side of the lens. Attempt: \frac{1}{f}=(n-1) \left [ \frac{1}{R_1}-\frac{1}{R_2} +...
  20. D

    Magnification due to a Diverging Lens

    Homework Statement The focal length of the diverging lens is 74 cm. If an object with height h = 0.6 cm is located at d = 37 cm, what is the height of the image? Homework Equations Thin-Lens Equation: (1/do)+(1/di)=1/f Magnification Equation: m=-di/do The Attempt at a...
  21. fluidistic

    Prove 4f is the Min. Distance Between Conjugate Points for Thin Lens

    Homework Statement Show that the minimum distance between 2 conjugate points (real object and image) for a positive thin lens is 4f.Homework Equations \frac{1}{f}=\frac{1}{S_o}+\frac{1}{S_i}.The Attempt at a Solution I assumed the lens to be biconvex (though I know that I can't. There are so...
  22. G

    Lens Design: Considerations for Lens Maker

    What considerations would a lens maker need to take into account when designing a lens? So on top of the chromatic aberrations, glass type and focal length, I have: Lens Thickness Magnification Resolving Power Radius of Curvature Shape(ie cylindrical, spherical, plane) Type(ie convex...
  23. S

    Real Object, Images formed by a single converging or diverging lens

    Homework Statement Starting with a real object, which of the following statements are TRUE about the image formed by a single lens? (Choose ALL correct answers, e.g. B, AC, CDF.) A) For a converging lens an object has to be placed between the focal length and the lens in order to form a...
  24. M

    Calculating Lens Power for New Eyeglasses

    Homework Statement A middle-aged man starts to wear eyeglasses with lenses of 2.0 D that allow him to read a book held as close as 25 cm. Several years later, he finds that he must hold a book no closer than 35 cm to read it clearly with the same glasses, so he gets new glasses. What is the...
  25. T

    Understanding Camera Zoom Lens Calculations

    Homework Statement A digital camera has a 3x zoom lens whose focal length can be varied between 6-18mm. The lens is assumed to be thin. The image is formed on a CCD sensor whose diameter is 10mm. 1. How large an object can be captured with the camera if the object is at distance of 10m from...
  26. jacksonpeeble

    What is the area of the sun's image on the paper?

    Homework Statement A camper is trying to start a fire by focusing sunlight onto a piece of paper. The diameter of the sun is 1.39e9 m, and its mean distance from the Earth is 1.50e11 m. The camper is using a converging lens whose focal length is 10.8 cm. (a) What is the area of the sun's...
  27. A

    Optics-maximum lens resolution and difraction limit

    Hi guys, I have a very simple question that arises in a photo forum in Brazil. Some guy put a formula to calculate the maximum resolution possible in a camera lens based on their aperture. The formula is 1800/N = (maximum resolution in lpmm) Were 1800 é a constant and N is the F stop of the...
  28. D

    Focal Length of Lens: Object 5 cm Tall, 10 cm Away

    An object 5 cm tall is 10 cm from a convace lens. The resulting image is one fifth as large as the object. What is the focal length of the lens? I have been doing questions involving focal lenght, but not when the resulting image is a fraction of the original image. i do not know where to...
  29. S

    Magetic lens electron beam bremsstrahlung

    I am trying to find information about the creation of bremsstrahlung due to the convergence or deflection of an electron beam using an magnetic lens. I can not find any information about the creation of bremsstrahlung when electron beams pass through magnetic lenses, I have only found...
  30. W

    Thickness of lens and its focal length

    I'd like to ask does thinner convex lens give a shorter focal length? If so, why is it? thanks very much~~
  31. A

    Solving a Plano-Convex Lens Problem: The 100th Bright Ring

    Homework Statement A plano-convex lens having a radius of curvature of r = 4.00m is placed on a concave glass surface whose radius of curvature is R = 12.0 m. Determine the radius of the 100th bright ring, assuming 500-nm light is incident normal to the flat surface of the lens. Homework...
  32. R

    Paraboloidal Wave Conversion via Biconvex Lens

    Homework Statement Show that a paraboloidal wave centered at the point P1 (x,y, z1) is converted by a biconvex lens of focal length f into a paraboloidal wave centered about P2 where 1/z1 + 1/z2 = 1/f. Homework Equations The Attempt at a Solution if U1(r) = A0/(z-z1)...
  33. N

    Calculating fD for a Diverging Lens: Is it Possible?

    Homework Statement Calculate a value for fD (the focal length of the diverging lens). Would this experiment be possible if fC > |fD|? Homework Equations Fcombo= (dodi)/(do+di)= (25*46)/(25+46) = 16.2 cm 1 - 1 = 1...
  34. B

    Optics : Lens Combinations with laser beam problem

    Hello. I've been struggling with this problem for some time, and honestly I do not know how to solve it. Homework Statement Two positive lenses are to be used as a laser beam expander. An axial 1.0 mm diameter beam enters the short focal length positive lens, which is followed by a...
  35. L

    Solving for Magnification in a Microscope

    1. Your task in physics laboratory is to make a microscope from two lenses. One lens has a focal length of 2.8 cm, the other 1.1 cm. You plan to use the more powerful lens as the objective, and you want the eyepiece to be 15 cm from the objective. What is the magnification of your...
  36. O

    Is it possible for a given lens to act as converging lens

    Question: Is it possible for a given lens to act as converging lens in one medium and a diverging lens in another? What i was thinking: Yes. Let say we put the lens underwater. It slows the light down and turns the image upside down as it passes through the converging lens, turning it...
  37. C

    What is the Ray Tracing Diagram for a Concave Lens with f < do < R?

    Homework Statement I have a concave lens where f < do < R. I have to provide a ray tracing diagram. The Attempt at a Solution I drew the focal ray through the focus and parallel to the principal axis. I drew the principal ray parallel to the principal axis then through the focus. I...
  38. L

    Understanding Thin Lens Formula: Image Location & Projection

    Hi, in questions involving lenses, when using the "thin lens formulae" if my di is negative doesn't that mean the image is on the other side of the lens? in this example however it doesn't seem this holds true.. A doctor examines a patient's skin lesion with a 15 cm focal length...
  39. G

    Solving Camera Lens Problem for Film Size of 24x36mm

    The actual frame size of "35-mm" film is 24 mm x 36 mm. You want to take a photograph of your friend, who is 1.70 m tall. Your camera has a 60.0 mm focal length lens. How far from the camera should your friend stand in order to produce a 36.0 mm-tall image on the film? i thought you would...
  40. G

    Optical Lens Combination Problem: Calculating Image Location and Magnification

    A converging lens of focal length 7.94 cm is 19.7 cm to the left of a diverging lens of focal -6.04 cm. A coin is placed 12.2 cm to the left of the converging lens. A) Calculate the location of the coins final image. B)Calculate the magnification of the coin's final imag. The equation i...
  41. S

    Focal Length of a Plano-convex Lens

    The given problem: What is the focal length of a Plano-convex lens, assuming parallel rays of light from s=∞ is traveling from the flat end of the lens. The lens is a glass hemisphere of radius R. Additionally the index of refraction of glass is higher than that of air. Homework...
  42. K

    Range of Powers of Eye Lens - Optics Question

    Homework Statement The human eyeball is approximately spherical with a diameter of around 25mm. At the back of the eye is the retina, while at the front is a compound lens comprising the cornea (of fixed focal length) and the lens itself (with variable focal length), which can be...
  43. G

    Thin Lens & Images: Real, Inverted & Smaller Objects

    Homework Statement Under what conditions will a thin converging lens form: a) a real image, b) an inverted image, and c) an image smaller than the object? Homework Equations none The Attempt at a Solution I have concluded that: a) the object needs to be outside the focal...
  44. B

    Calculating image locations with thin lenses

    Homework Statement For each thin lens shown in the figure , calculate the location of the image of an object that is 18.5 {\rm cm} to the left of the lens. The lens material has a refractive index of 1.50, and the radii of curvature shown are only the magnitudes...
  45. B

    How Far Are You From This Lens?

    Homework Statement You are standing in front of a lens that projects an image of you onto a wall 2.80 {\rm m} on the other side of the lens. This image is three times your height. How far are you from the lens? Is your image erect or inverted? What is the focal length of the lens? Is the...
  46. B

    Ray Tracing and Image Formation with a Concave Lens

    Homework Statement If the focal length of the concave lens is -7.50 cm, at what distance d_o from the lens should an object be placed so that its image is formed 3.70 cm from the lens? What is the magnification m produced by the concave lens described in above? Where should the object be...
  47. J

    Lens equation: pretty simple probably

    Homework Statement A converging lens ( f = 10.4 cm) is held 8.80 cm in front of a newspaper, the print size of which has a height of 2.04 mm. Find the image distance (in cm) and the height (in mm) of the magnified print. D= _____cm H= _____cm Homework Equations 1/f=1/do+1/di...
  48. N

    Optics: Ray matrix for a thin lens

    Hi guys I wonder if you can explain this to me. In http://en.wikipedia.org/wiki/Ray_transfer_matrix_analysis#Table_of_ray_transfer_matrices it says under "Thin lens" that the ray matrix is given by \left( {\begin{array}{*{20}c} {r_{final} } \\ {r_{final}^' } \\ \end{array}} \right) =...
  49. C

    Contact Lens: How to focus light 1mm away

    So, I've been wondering. Anyone know what shape/prescription a contact lens would have to be in order for an eye to be able to focus on something 1mm away (assuming the distance of focus in the eye is around 4 cm)? Does it have to do with focal length of the lens?
  50. C

    How to determine a lens width?

    I am wondering... say an object was put directly on a lens and you wanted the projected image to focus at around 3 cm on the other side. How do you determine how wide the lens has to be? (please see attachment)
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