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. grandpa2390

    Quick lens problem, is f positive or negative

    Homework Statement the focal point is said to be real and positive for concave mirrors and virtual and negative for convex spherical mirrors. what if the problem gives you the focal point for a spherical convex as 15 cm. am I supposed to take it that the the focal point should be plotted one...
  2. P

    Solving Compound Microscope Lens Length Problem

    Homework Statement The barrel of a compound microscope is 15.9 cm in length. The specimen will be mounted 1.17 cm from the objective, and the eyepiece has a 5.00 cm focal length. Determine the focal length of the objective lens.Homework Equations I am using the mirror equation. The Attempt at...
  3. 1

    Deriving the Point Image Equation for a Spherical Interface

    Homework Statement A biconvex lens of refractive index ##n## and radius of curvature ##r## and focal length ##f## floats horizontally on liquid mercury such that its lower surface is effectively a spherical mirror. A point object on the optical axis a distance ##u## away is then found to...
  4. P

    Finding Distance d for Infinity Image: Diverging and Converging Lens Problem

    Homework Statement An object is placed 12.8 cm to the left of a diverging lens of focal length -6.35 cm. A converging lens of focal length 12.8 cm is placed a distance of d to the right of the diverging lens. Find the distance d that places the final image at infinity Homework Equations...
  5. P

    Hi/ho problem -- Lens magnification

    Homework Statement An arrow h0 = 2.20 cm long is located 74.0 cm from a lens, which has a focal length = 30.6 cm. If the arrow is perpendicular to the principal axis of the lens, as shown in the figure below, what is its lateral magnification, defined as hi/h0? I am given: ho=2.20 cm. do 74.0...
  6. W

    Optical System with Diverging Lens and Concave Mirror

    Homework Statement A diverging thin lens and a concave mirror have focal lengths of equal magnitude. An object is placed (3/2)f from the diverging lens and the mirror is placed a distance 3f on the other side of the lens. Using Gaussian optics, determine the final image of the system after two...
  7. D

    [Optics] Concave-Convex lens radius

    Hi, I'm trying to solve the following problem: "What is the optical power (in dioptres) of a concave-convex eyeglass lens (n = 1.5) with the radiuses r1 = 12cm and r2 = 18cm?" The attempt at a solution: I'm usually solving such questions with the following equation: ## \dfrac{1}{f} =...
  8. AwesomeTrains

    Ray transfer matrix - Plano convex lens

    Homework Statement I have to find the ray transfer matrix for a Plano convex lens, with a 5 cm radius and refraction index n=1.8. I'm supposed to use the paraxial approximation. Attached a homemade picture of the lens. Homework Equations Refraction at a curved surface: \begin{pmatrix} 1 & 0\\...
  9. S

    Silvering of Plano-Convex Lens

    If the plane surface of a plano-convex lens in silvered then which of the following statements is true? 1. it acts like a convex mirror 2. it acts like a concave mirror 3. it acts like a concave lens 4. no changemy attempt--- the incident ray on the convex surface of the plano-convex will...
  10. AdityaDev

    Radiation pressure from light source

    The energy of photon is $$E=\frac{hc}{\lambda}$$ Now if we have an isotropic point light source of power P, Number of photons $$N=\frac{P}{E} = \frac{P \lambda}{hc}$$ Hence one can find the change in momentum and hence the force exerted by a beam or light sources. But let's say we keep an...
  11. AdityaDev

    Can a Convex Lens Converge a Tilted Wavefront?

    If I have a parallel beam of light parallel to x-axis, with the speed of light varying from bottom to top. Let it decrease from bottom to top. (To get such a beam one can pass the beam through a glass slab normal to its surface, whose refractive index increases linearly from bottom to top). Now...
  12. AdityaDev

    Modified plano-convex lens doubt

    I was thinking about the situation given my text about a plano convex lens which was produced with a manufacturing defect. It's plane surface is tilted outwards by a small angle 'z'. In the text its written that when a parallel light beam enters the lens parallel to x-axis , it will still be...
  13. M

    Focal length from thin lens to object distance

    Hello, I've come across an problem that requires the lens to be at least about 350 mm away from the object. Object to be examined is 80 mm tall and imaging plane is either 11 mm or 25 mm tall. I've tried to calculate required focal length, but have not succeeded. Distance from lens to imaging...
  14. B

    How Do You Calculate the Diameter of a Camera Lens Based on a Photograph?

    Homework Statement How we can determine The diameter of the lens of the camera approximitly that this picture took with that? ( we know that lens of the camera made by some parts but we count them as a thin one in Practical calculations ) Homework Equations m = q / p 1/f = 1/q + 1/p f =...
  15. W

    Calculating Camera Lens Diameter with a Ruler

    Hello guys, I was wondering if you could guess or even calculate the diameter of a camera lens with a picture of a ruler.
  16. hemness

    Straight light beam in opaque water

    Hello! As this is my first post - I'm Mike from Poland, currently studying product design on Academy of Fine Arts in Warsaw. I'm working on a sculpture - light installation. I want to achieve an effect of a regular beam of white light - light cylinder in slightly opaque water. Sort of similar...
  17. A

    Do multiple lens cameras refract light differently to a single lens ones?

    Why do high end camera modules have so many glass lenses, apart from the necessary lenses for focus and zoom why is it that in cameras like DSLR cameras there are so many low power lenses where a few high power ones would work do the same job, do the lenses diffract light differently when...
  18. T

    Ray Tracing for Convex Lens: How to Determine Image Distance and Realness

    Homework Statement [/B] B) Is the image real or virtual? Explain. C) Using the lens equation, find the image distance. 2. Homework Equations 1/di + 1/do = 1/f The Attempt at a Solution A) B) The image is real because it is on the opposite side of the lens as the source of light. C) do =...
  19. aditya ver.2.0

    Can dispersion of light take place through lens?

    Can dispersion of light take place through lens, i.e. can lens (incl. Convex and Concave) scatter white light into its constituents?
  20. M

    How does the power of a lens affect its ability to focus light?

    So I've been doing some experiments, using bottles filled with various liquids and timing how long they take to burn paper which is placed at the focal point (where the light was focused). I've noticed that using denser liquids with high refractive indexes lower the focal length, and thus...
  21. N

    Optics Lab: Combined Lens Systems

    Homework Statement Given a system composed of a convergent lens and divergent lens (separation d between), how do I best calculate the focal length of the divergent lens? What is the best way to set up the system (converging lens first? diverging lens first?). There is plenty of documentation...
  22. P

    Any good softwares for drawing optical schematics?

    Hi all, Are there any good softwares for drawings schematics like this? I need to make and insert such images in my thesis report.
  23. C

    Can I Use a Telecentric Lens with an Afocal Telescope?

    I have a nearly afocal telescope. I want use a telecentric lens with this telescope. My question is that ı need a telescope focal point or ı can use a telecentric lens directly with this afocal telescope?
  24. M

    Image seen by human eye through a convex lens

    Greetings, I don't have a magnifying glass/convex lens otherwise I would try to confirm this by experiment. Maybe I'll get one soon but to get things started. Let's say you have an object, with its own light source, and a convex lens with focal point f. The object is beyond 2f away from the...
  25. H

    Why do different types of lenses have different effects on image size and focus?

    So for BiConvex Lenses, increasing the lens radius (by making the lens fatter) brings the image and focus closer to the lens, thus making it smaller given constant object position. As demonstrated in this demo http://micro.magnet.fsu.edu/primer/java/lenses/lensvariations/index.htmlYet for the...
  26. mishima

    Gravitational Lens with home scope?

    Would it be possible to capture a gravitational lens with a decent amateur scope coupled to a reasonable CCD?
  27. K

    Finding the focal length of a negative lens without another lens.

    Homework Statement A simple method for determining the focal length of a negative lens is shown below. Prove this is true. Homework Equations The Attempt at a Solution The linear magnification formula relates magnification, the distance from the lens to the image (i), the distance from...
  28. A

    Help with Focusing Lens Block

    Posted a while back but to no avail. I've since done some tinkering but need a little bit of help perfecting the math. I've constructed an experimental version of the above set up with success. Moving the plano-concave element away from the plano convex element brings the focal point towards...
  29. F

    Where is the image formed when a lens is placed next to an aquarium?

    Homework Statement There is a small shiny object in a big aquarium, which is formed like a cuboid and filled with water. The plan site of a plano-convex lens with a focal length f is put on the wall of the aquarium from outside. The object is located on the optical axis of the lens. The...
  30. S

    Calculating Object-Lens Distance for Diverging Lens Optics

    Diverging lens has focal length 6mm and image magnification 0.5. What is the distance between object and lens? I used the fact that distance image to lens/distance object to lens = 0.5 and the lens maker formula with f=-6 and combined the two formula but this gives distance = 18mm, when answer...
  31. D

    How can you use Snell's law to find the image formed by a thick lens?

    A window of a submarine is 30 cm thick, and is underwater. The index of refraction of the window is 1.65. The index of refraction fo th eocean is 1.35. The index of refraction inside the submarine is 1.00. A scuba diver is 1 meter away from thw window. Where does his image form?I used n1/d_o...
  32. D

    Thermal expansion/contraction of lens

    Application: to measure the thermal strain of optical lens. Due to temperature variation the lens surface is expanding / contracting in radial direction with two extreme operating temperature. (-40C to +70C ) Optical lens is SF56A (CTE - 7.9*e-6 per Kelvin) What to do: I need to measure...
  33. J

    Calculating Magnification with lens, an object, and a screen.

    Homework Statement A lens with focal length fo = 9 cm forms an image of an object placed a distance d=3.7fo to the left of the lens, onto a screen to the right of the lens. The distance L from object to image is fixed. The lens is now moved toward the screen a distance x until an image is...
  34. A

    Anamorphic and Spherical Lens Focusing

    New to the forum but stumbled upon this and thought it might be beneficial to query more scientifically minded individuals. I am a filmmaker and use a variety of lenses to acquire certain looks. One of which is anamorphic cinematography. (http://www.red.com/learn/red-101/anamorphic-lenses)...
  35. E

    Optics - Lens Selection / Geometry

    Hello everyone! I recently bought a small raspberryPi board, with its small "camera board". (link for camera reference) I want to use a CS lens on this camera (CS lens from the security camera industry). I have been able to attach the lens, and it focuses very good, yet not "excellent"...
  36. F

    What is the relationship between numerical aperture and resolution in lenses?

    Hello Forum, The numerical aperture NA of a lens is usually a parameter (adimensional) that indicates the lens ability to collect light. The concept of NA is usually introduced in fiber optics where we are concern with launching light into the fiber. But NA is also discussed in microscopy...
  37. H

    Quick question on mirror and lens scenario

    I attached a picture with 3 questions? My first question is, I know that for a convex or concave mirror, If I shine a light at an angle to the middle of the mirror the light will reflect with the same angle. Will the angle be the same if I shine the light at the concave/convex mirror if it...
  38. E

    Local linear increase of the lens

    Homework Statement Hello! I need to find a local linear increase in the field of the lens. I have Listing of Field Curvature Data. It contains vectors of - Y height, Tan Shift, Sag Shift, Real Height, Ref. Height, Distortion. I can not understand how these data get what I need. Homework...
  39. D

    Radius of curvature of second lens surface

    Homework Statement A lens of power of -5.0D has a surface which is convex of radius of curvature of 15.0cm. The lens is made of material of refractive index of 1.50. What's the radius of the other surface of lens? Homework Equations The Attempt at a Solution since power = 1/f...
  40. D

    Radius of curvature of glass and water lens

    Homework Statement by taking the lower curvature as r1 , and the upper curvature as r2 , i don't know whether r1 is 20cm , r2 is 10cm or vice versa. But according to the ans r1= 10 cm , r2= 20cm . why is it so? Homework Equations The Attempt at a Solution
  41. D

    Focal length of combined glass lens and water lens

    Homework Statement please refer to the photo, Homework Equations The Attempt at a Solution why can't I directly use the lens maker formula to get the ans ? my working is 1/f = ( (1.5-1.33) /1.33) x ( (1/20) + 0 ) ...finally , i get my f = -160cm. the radius of curvature of...
  42. S

    Which is correct: r1 and r2 should have different signs or be the same?

    Homework Statement referring to the notes attached , r1 is negative beacuse it's concave to the incident light , r2 is positive bacuse it's convex to the incident light. ( incident light move from left to right. ) , but my another book states that the r1 is and r2 have the same sign , which is...
  43. E

    Focal length of converging meniscus lens filled with a liquid

    Homework Statement A converging meniscus lens is made of glass with index of refraction n = 1.55, and its sides have radii of curvature of 4.5 cm and 9 cm. The concave surface is placed upward and filled with carbon tetrachloride which has index of refraction n' = 1.46. Determine the focal...
  44. M

    Is a Corona Flash System Using Fiber Optics and Lens Physics Possible?

    Whom might be talking on this area?
  45. Greg Bernhardt

    Understanding the Thin & Gaussian Lens Equations

    Definition/Summary A lens is most often used to focus light rays from an object to form an image. It can also be used to collimate light rays from an object, or to bring a collimated beam of light rays to a focus. Equations See "Extended explanation" for definitions of terms. The well-known...
  46. K

    Optics: Lens for capturing light from parabolic reflector

    I was wondering what type of lens would be best for capturing the light incoming from a parabolic reflector into a container? The Fresnel lens looks like a good candidate, but I am still not quite sure. Does anyone have any insight on this subject? Just for info, the parabolic lens redirects...
  47. A

    Measuring the focal length of a deformable lens

    Hello all, My lab recently purchased a deformable lens, which can change its focal length from 140 mm to 40 mm and anywhere in between, based on current applied to it. I'm wondering how to use a beam profiling camera to measure the focal length of this lens at various current levels. We...
  48. S

    Why Does a Fresnel Lens Create an Upright Image in a Galilean Telescope Setup?

    I have a Fresnel lens which is equal-ant to a Plano Convex lens, Consider object on one side and my eye is on the other side of the lens, when I see through that lens I always do see an upright image of same size even if I flip the lens, Can anyone please tell me geometric optics equal-ant of...
  49. L

    Lens to lens distance is not 2f in "4f system"

    Dear, I studied 4f system and I've got a question. As far as I know, 4f system is optical filtering system (attached file). In the configuration in the attached file, region between L1~L2 is infinity optics(ray components from P1 is parallel with each other) so that distance between L1~L2...
  50. J

    Refractive Index - Lens question

    Homework Statement A double concave lens has equal radii of curvature of 15.1 cm. An object placed 14.2 cm from the lens forms a virtual image 5.0 cm from the lens. What is the index of refraction of the lens material? A. 1.98 B. 1.9 C. 1.84 D. 2.06 Homework Equations 1/f = (n – 1 ) (1/R1...
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