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. N

    Images in a diverging lens are always virtual. when an objectis placed

    images in a diverging lens are always virtual. when an objectis placed betweenthe focus and optical centre of a converging lens, the image is also virtual. what are the differences between these virtual images? explain by studying the 4 characteristics of each image. i have no idea of...
  2. J

    How can I find the focal length of a lens silvered at one face?

    Homework Statement Its not a specific question but a general one to solve similar questions. I need to find focal length of a lens silvered at one face Homework Equations The Attempt at a Solution I know a convex lens silvered at one face will behave as an effective concave lens...
  3. C

    Help Solve Lens Projector Distance Puzzle!

    I have this in my home work and i am not 100% on if i have it right or not A converging lens with a focal length of 25 cm is used to make a slide projector. If the image is to be projected onto a screen 10m away, how far should the lens be located from the transparency? I did it like...
  4. D

    Facts about Mirrors and Lenses: What You Need to Know for Your Final

    Homework Statement I am studying for my final and just want some clarification on mirror facts. Homework Equations The Attempt at a Solution Convex: focal length = negative and concave is opposite positive Diverginging = - image dist converging just the opposite or positive if...
  5. D

    How to tell is a two lens converging system is inverted or not

    Homework Statement A compound microscope consists of two converging lenses. Lens 1, called the objective, is a distance 61.0 mm from lens 2, called the eyepiece. The objective is placed in between the object and the eyepiece. The objective has a focal length of 15.0 mm, and the eyepiece has...
  6. K

    Converging and Diverging Lens

    Homework Statement Which type of lens can have a magnification greater than 0? Which statement is most complete? A) Both, and both converging and diverging lens can have any m > 0. B) A diverging lens only. C) Both, but a converging lens has m > 1 while a diverging lens has m between 0...
  7. H

    Solving Dielectric Lens Electric Field Equation

    Homework Statement In the figure the left surface of a dielectric lens is that of a circular cylinder, and the right surface is a plane. If E1 at point P(r,45,z) in region 1 is 5\hat{a}_{r}-3\hat{a}_{\phi }, what must be the dielectric constant of the lens if the electric field in the...
  8. R

    Optics: finding the width of an image produced through a lens

    Homework Statement This is more of a general conceptual question. When finding the image produced through a convex or concave lens, I know that you can use the equation magnification = (height of image/height of object) to find the magnification of the image produced. But does this...
  9. N

    Focal Length & Concave Lens: Multiple Images?

    is it true when we use concave lens, we can obtain focal length when we get the sharp image.. is it possible to get more than one sharp image when we change the object distance (distance between object and lens)
  10. F

    Geometrical optics - lens floating in mercury

    Homework Statement Consider a thin bi-convex lens with refractive index n which has spherical surfaces with equal radii of curvature r and a measured focal length f. The lens floats horizontally on the surface of liquid mercury so that its lower surface effectively becomes a spherical mirror...
  11. H

    Range of movement of a lens?

    Homework Statement In a 35 mm single lens reflex camera (SLR) the distance from the lens to the film is varied in order to focus on objects at varying distances. Over what range must a lens of 45 mm focal length vary if the camera is to be able to focus on objects ranging in distance from...
  12. B

    Understanding Thin Lens Equations: Solving for Image Distances and Focal Length

    Homework Statement I am given 5 distances to place the object relative to the lens. I then need to calculate each of the images distances for all 5 and record them. Once I have that done, I am to conduct a graph of 1/q vs 1/p. I then need to answer these questions: 1- Is the slope of your...
  13. F

    How does an image formed by a cylindrical lens look like?

    Hello forum, I have been trying to understand how a cylindrical lens (plano cylindrical) forms images. The images are blurred, smeared, only in one direction. I know that this type of lens focuses parallel rays to a focal line instead of to a focal point... So the smearing occurs along...
  14. S

    Infinity optics - position of tube lens

    Hi, I was hoping someone would be able to help me with a microscopy problem that has been puzzling me for a while. I'm building a basic microscope from scratch using a 50x long working distance Nikon objective (LU Plan ELWD, wd = 10.1mm, NA = 0.55). The sample is illuminated from above using...
  15. A

    Is This Custom Lens Design Suitable for My Needs?

    Hello Need to verify please if the following custom design lens is reasonable -- Sensor: CMOS sensor, 1/3”, 6μm x 6μm pixel, Wide VGA 752H x 480V, 4.55mm x 2.97mm Imaging Area -- Focus: 50m till 200m -- Lens: f2.8; Focal length=34mm; Diameter=13mm Pay attention I am not a physicist...
  16. C

    Question about sign convention for R1 and R2 when using the lens maker's formula

    Hi! I'm having some trouble with optics. When we have convex, planoconvex, concave, planoconcave, and meniscus lenses, I don't understand how to substitute with the sign for R1 and R2. How do I determine whether the radius of a side is negative or positive? A book that I'm using said to take...
  17. N

    What physical aspect of a converging lens affects magnification

    Probably a complete newb question and I know magnification is dependent on how severely the light is bent but what physical aspects cause the light to bend more/less? I was told it's the thickness so do thin or thick lenses bend light more severely? and which would result in greater...
  18. Y

    Infinite-distance object lens depiction

    This is rather simple but has me stumped. The assignment prompts me to create the construction rays of an object at infinity, refracting through a thin converging lens, with image focusing at focal point f. So where do the rays originate from? My guess was perhaps it means just a light...
  19. B

    Help with lens selection and arrangement for maginification

    Hi guys. any help with this would be greatly appreciated. I am trying to make a device like a periscope which is 100MM in length but has a diameter of 5mm. the viewing end of the periscope can be much wider to accommodate an eye optic, but the other end does need to retain the diameter of 5mm...
  20. K

    Understanding Lens Flare: Causes and Observations | Light Phenomenon Explained

    Hey I've been looking around about lens flare's within the eye. well not necessarily lens flares, but the category it falls under and what exactly is it. Just wondering if anyone here know's where I can find it or tell me what exactly it is and causes it. Basically when I look at street...
  21. S

    Focal length equation from Radii of Curvature and refractive index of lens

    Hi all, I'm looking for an equation which will give me the focal length of a biconvex lens given that we know both Radii of curvature, the thickness of the lens and the refractive index inside and outside. An equation is given on wikipedia here http://en.wikipedia.org/wiki/Focal_length as I...
  22. F

    Spherical Aberration of Lens

    Homework Statement Hi, I have a question regarding my physics lab assignment. Last week I performed an experiment on the focal length of a biconcave lens using different part (using the radius of the lens) of the lens. This is done by completely covering the lens with a cardboard except for...
  23. M

    Calculating refractive index using lens

    we can calculate the refractive index of liquids like water using a converging lens and mirror by the standard method . r.index of water is less than that of lens(glass) . now taking mercury, whose r.index is > glass, can we do the same experiment and find its r.index ? i believe the answer...
  24. L

    Thin Lens Problem: Solving for Object Distance w/ Magnification

    Homework Statement (a) How far from a 50.0-mm-focal-length lens must an object be placed it its image is to be magnified 2.00X and be real? (b) What if the image is to be virtual and magnified 2.00X? Homework Equations Thins Lens Equation: 1/f = 1/do + 1/di Magnification...
  25. F

    Why does a lens automatically produce perspective?

    Hello Forum, can anyone explain why a camera, a lens, automatically creates perspective in an image? Is it explainable with ray tracing? thanks fisico30
  26. P

    Can a Gravity Lens Loop Amplify Distant Objects in Space?

    Thought experiment. Imagine building two optical mirrors around the sun an astrophysical body of the right mass, lined and diametrically opposed, at the right distance so that the sun is acting as a gravitational lens. Mirror A reflects the light from any extrasolar object and directs...
  27. N

    Can better sensors extract unlimited info from old lens?

    I placed this in quantum department but since no comments came either it belongs here or is too trivial. Please comment. MY POST IN QUANTUM PH. FORUM ... " This problem I encountered in my photography forum. A new model of camera comes out with a much higher megapixel sensor (Nikon D800...
  28. A

    Optics Instrumental with thins lens

    Homework Statement In a thick lens, how we do to get the primary and secondary principal planes Homework Equations (1/Si)+(1/So)=1/f The Attempt at a Solution I tried to get to get that with the Newtonian equation
  29. N

    Can better sensors extract more info from old lens w/o limits?

    This problem I encountered in my photography forum. A new model of camera comes out with a much higher megapixel sensor (Nikon D800, 36mpix). I argue that such sensor will need new lenses to be meaningful. Others claim that a given lens performance (here resolution) is always utilized by a new...
  30. D

    Lens maker's equation used correctly?

    Homework Statement An object is placed 60 cm from a thick double convex lens, with faces of radii of curvature 20 cm and 30 cm, with thickness of 2 cm, and index of refraction is 1.5. Find the position of the image...
  31. P

    Calculating Focal Points of a Thick Lens

    Homework Statement A thick lens has an index of refraction of 1.560, thickness of 3.0cm, and radii of curvature of R1= -4.50cm, R2= -3.60cm. Calculate the positions of the focal points (relative to the vertices). Homework Equations \frac{n}{s}+\frac{n'}{s'}=\frac{n'-n}{R} ffl =...
  32. M

    Matrix optics; simple lens system

    Homework Statement Calculate the matrix for the optical system which takes rays from the object plane to the image plane for a simple lens and show how this leads to 1/v = 1/u + 1/f Also show that the matrix can be written in the form \left[ \begin{array}{cc} 1/M & b \\ 0 & M...
  33. M

    Where Will the Coin's Final Image Be and What Will Its Magnification Be?

    Homework Statement A converging lens of focal length 7.740 cm is 19.7 cm to the left of a diverging lens of focal length -5.51 cm. A coin is placed 18.2 cm to the right of the diverging lens a. Find the location of the coin's final image. b. Find the magnification of the coin's...
  34. N

    Thin Lens Formula: Deriving 1/f = 1/S_O + 1/S_I

    Hi The thin lens equation we know is given by \frac{1}{S_O} + \frac{1}{S_I} = (n-1)(\frac{1}{R_1}-\frac{1}{R_2}) assuming light is incident from air. The "usual" way to derive the thin lens formula (aka the Gaussian Lens Formula) is to say that when looking at the system when either the...
  35. J

    Can you have an anti focal point of a lens?

    Can you have an "anti" focal point of a lens? Hi, Imagine putting a convergent lens in the path of a laser beam. I put a small light meter at the focal point of the lens. If I move the lens along the beam will there be positions of the lens where the light paths through it completely...
  36. K

    The radii of the curvature of the spherical surfaces which is a lens

    the radii of the curvature of the spherical surfaces which is a lens of required focal length are not same. it forms image of an object. the surfaces of the lens facing the object and the image are interhanged. will the position of the image change?
  37. F

    What is a Complex Lens? Convex or Concave?

    When an object is placed at the principle focus of a complex lens, then the image is A) larger and inverted B) smaller and inverted C) the same size and inverted D) not formed at all Incorrect. Your answer=C, Correct answer=D MY QUESTION: WHAT ON EARTH IS A COMPLEX LENS? CONVEX OR CONCAVE? thanks
  38. A

    Focal length calculations for a double convex lens?

    From what I recall, determining the focal length of a double convex lens just involves an infinite light source and holding the lens close to an image-capturing surface such as a wall and adjusting the distance until the image is at its sharpest...the distance from the lens to the surface is the...
  39. Q

    Derivation of the thin lens equation?

    'm currently reading chapter 27 of the Feynman lectures, where he derives the thin lens equation for a single refracting surface. He arrives at the equation h^2/2s + nh^2/s' = (n-1)h^2/2r Where s is the object distance, s' is the image distance, n is the index of refraction of the second...
  40. Y

    What is the Focal Length of a Convex Lens?

    I am trying to find the focal length of a convex lens, so i let the sun shine through my window to create an image on my wall. Is that image the focal point or is it just the distance of the image? And if it is the distance of the image, how do I put it into the thin lens equation, since the...
  41. B

    Optics(Converging lens and Diverging lens)

    Homework Statement http://www.imageurlhost.com/images/r0its2lyef7v3s0ppms2.pngHomework Equations Mirror Equation (1/q) + (1/p) = (1/f) = (2/r) Magnification M = (q/p) for two lenses M1 & M2 Total magnification = M1*M2The Attempt at a Solution we have p1 = 40cm and f1 = 30cm then the image...
  42. S

    Number of images formed by two concave lens, one displaced from optical axis

    Homework Statement A biconvex symmetrical lens is cut in two halves and placed as shown in figure. if a point object is placed in the left how many images will be formed options - (a) Two images (b) Three images Homework Equations The Attempt at a Solution As I...
  43. Spinnor

    Dragon fly eye, lens very precise?

    Is the exact shape of the lens of a dragon fly ommatidium genetically encoded? I guess that the radius of curvature for both the front and back surfaces of the lens is somehow genetically encoded, call them r_f and f_b? I guess nature has come up with an optimal design for the dragonfly lens...
  44. S

    Diverging lens problem? finding focal length

    A diverging lens is used to form a virtual image of an object. The object is 88.0 cm in front of the lens, and the image is 44.0 cm in front of the lens. Determine the focal length of the lens. 1/f = 1/do + 1/di since do is 88cm infront of the lense, that would keep the 88 positive, and...
  45. F

    Telecentric Lenses: Benefits & Applications

    Dear Forum, does anyone know what a telecentric lens or optical system does? I just know that it provides a projected instead of perspective view of small objects... Why is that useful? thanks fisico30
  46. T

    Fresnel Lens Concentration Ratio

    Homework Statement Hey guys, I am part of a group building a solar oven. It will consist of insulated sides and a glass window on the top. Rather than using reflectors we want to salvage a Fresnel lens from an overhead projector to concentrate sunlight onto the glass window. Part of the...
  47. C

    Light passing through a lens diffraction phenomenon

    A light passing through a lens will be focused for a converging lens. However, to look at it carefully, it'll not converge to a single point but to a certain size. The size of it and some fringes surround it is actually a diffraction phenomenon. I don't really understand that the usual...
  48. G

    Calculating Angular Magnification of a Lens Without Knowing Object Height

    Homework Statement A small insect is placed 6.55 cm from a 7.00 cm-focal-length lens. Calculate the position of the image. Calculate the angular magnification. Homework Equations 1/f=1/do+1/di M=angular magnification=θ'/θ=angle of image/angle of object=N/f where N=near point The...
  49. F

    Thin-Film Interference: Coating a Lens - Answers found, explanation needed

    Thin-Film Interference: Coating a Lens -- Answers found, explanation needed! Homework Statement Boxed answers are the correct ones. Homework Equations 2L=(m+1/2)(λ/n) for constructive interference (maximum reflection, bright film) 2L=(m)(λ/n) for destructive interference (minimum...
  50. J

    Gravitational Lenses & Light Frequency: Same or Different?

    will light of all colors bend to the same extent or is it different for different frequencies?
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