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. A

    Find the axial resolution achieved for confocal microscope

    Homework Statement 2. Homework Equations F-number is f/d x0 = 1.2λ(fnumber) The Attempt at a Solution [/B] Fnumber1 = 0.2 Fnumber2 = 0.6 x01 = 180nm x02 = 540nmThese values seem large for depth resolution, is this correct?
  2. FritoTaco

    Finding Image Distance with a Converging Lens: Magnifying Glass Problem

    Homework Statement A magnifying glass has a converging lens of focal length 15.0 cm. At what distance from a nickel should you hold this lens to get an image with a magnification of +2.00? Homework Equations 1/f = 1/di + 1/do m = -di/do or hi/ho The Attempt at a Solution I tried to set it up...
  3. M

    Very basic convergence lens question

    Hello. I have a very simple question that I need answered for my science project. I am doing a project on the effect of the convexity of the lens on the intensity of converged light. (Lux?) I am using a class set which I haven't been able to get my hands on yet, but we are expected to be...
  4. A

    System of lenses with a light source at first focal point

    Homework Statement So I have this system of lenses with this problem: First lens: focal length ##f_1=50 mm## Second lens : focal length ##f_2=400 mm## Distance between them ##d=600mm## A small light source is placed at the focal point for the first lens. At the focal point for the second...
  5. UchihaClan13

    Refraction Formula For Thin Lens

    I was browsing about my optics books,completing numericals and stuff When I found a a statement called different lens formulas It had 2 formulas One,called the thin lens formula or rather the geometric sign convention formula was called 1/v-1/u=1/f(Symbols have their usual meanings) and another...
  6. R

    Need Aspherical Lens Equation (+20d, 55mm)

    Hello. I am not related to physics or any optics related field. I am in need of equation for +20d aspherical lens of diameter 55mm. Can anybody help me?
  7. F

    Gravitational Lenses: Does Gravity Distort Spacetime?

    If gravitational lens can "focus" light, is it possible with gravitation, so that the resulting gravitation would be strangely unhomogenous? (If it is a dumb/noob question just tell we pls.)
  8. Kompewt

    Focal length of thin converging lens

    Homework Statement An outdoor security camera has a simple lens with focal object length fo = 6.00 cm and perfectly focuses the image of a bird onto its detector located 9.00 cm away from the lens. The animal then flies away from the lens and the new focal distance is 8.00 cm. (a) How far did...
  9. moenste

    Find the position of the lens between two holes and screen

    Homework Statement An opaque card is pierced by two small holes 4 mm apart and strongly illuminated from one side. A lens on the other side of the card focuses images of the holes, 16 mm apart, on a screen 125 cm from the card. Find: (a) the position of the lens, (bc) the focal length. Why are...
  10. Andy Resnick

    The Lens Matters More Than the Camera: A Personal Story

    Sadly, my camera (Sony a850) is 'beyond repair'. It served with honor and distinction for 6 years, I took about 200k images with it. Until I replace it, I've been sharing my kids' Canon 1100D (Rebel T3)- an entry level camera- so I got a Nikon-EF adapter. Well. 6 years ago, when I...
  11. G

    How Do You Calculate the System Matrix for a Lens After a Beam Waist?

    Homework Statement A thin lens is placed 2m after the beam waist. The lens has f = 200mm. Find the appropriate system matrix. This is a past exam question I want to check I got right. Homework Equations For some straight section [[1 , d],[0 , 1]] and for a thin lens [[1 , 0],[-1/f , 1]]...
  12. davenn

    Is the Milky Way Visible with a New Wide-Angle Lens in Sydney's Night Sky?

    finally got a chance to get out and try out my relatively new Samyang 14mm ultra wide angle lens this is using the Canon 5D Mk3, 3200 ISO, 14mm f/l, f2.8, 20 sec exp. The view is to the SW I traveled for about 40 minutes to get south of Sydney and away from the main city lights and their...
  13. L

    Image formed by a plane-concave lens and a concave mirror

    Homework Statement An observer looks at an object of height 2 cm through a plane-convex lens of radius 20 cm and refraction index 1.5. There's a concave mirror of radius 30 cm 40 cm behind it, and the object is at the same distance of both the lens and the mirror. Find the images formed by the...
  14. Andy Resnick

    What can we learn about the Milky Way using an 85mm lens and static tripod?

    Here's a few stacks of the milky way I took last week, using an 85mm lens and a static tripod- 3.2s exposures. Two from the region around Cygnus: And a panorama closer to the horizon (12 stacks): This is about 13k x 11k pixels. At 100% the nebulae are still clear: Unfortunately, I...
  15. N

    I Double slit particle distribution with convex lens?

    In one double slit experiment, one physicist placed a convex lens before the back screen detector. The individual photons passed through the double slit then through the lens. The individual photons then go through the focal point, then a good distance after they reach the focal point they hit...
  16. N

    No interference pattern in double slit when there is a lens?

    Why does the interference pattern of the photon go away when one places a convex lens far away from the two slit to only show a particle build up of the two slits? This is the experimental set up, the lens is in place far after the photons pass through the two slit and hit the back wall in a...
  17. D

    Radiative Transfer Equation: Point Source and a Thin Lens

    Homework Statement Write the Radiative Transfer Equation for an isotropic incoherent point source a distance p away from a thin lens. Assume that scattering in air can be ignored but absorption cannot be ignored. Homework Equations 1. Radiative Transfer Equation (RTE): \frac{dw}{dt} = \left[...
  18. kelvin490

    Question about lens maker's formula

    I am trying to follow the derivation of lens maker's formula from the textbook "University Physics", p.1133 (https://books.google.com.hk/books?id=nQZyAgAAQBAJ&pg=PA1133#v=onepage&q&f=false ) I can understand the first equation because it is just the object–image relationship for spherical...
  19. F

    Finding lens diameter - German physics task

    Hey everybody, I'm right now trying to solve a question I found in a German physics competition 2006 concerning the diameter of a thin camera lens. I'm not able to find a solution, since there is basically nothing given. Here the task (I underlined phrases which might be important): A ruler...
  20. S

    Where to place a thin lens to couple a ray into a fiber

    Homework Statement i need to couple a ray (point source 15 deg) into a fiber with a small core diameter, the fiber located 8cm from the source. the focal distance of the lens is 1.5cm i need to choose 2 possible locations Homework EquationsThe Attempt at a Solution first suggestion: i placed...
  21. D

    Question about camera lens taking a picture

    Hey guys, Can someone give a basic explanation of why a camera can take a picture even if half of its lens is covered up? Thanks guys...
  22. H

    Simplest lens set up to reveal optical spectra of an object

    I have done basic experiments where a laser is shot thru a grating and a lens is inserted at the diffraction pattern to put the spectra back together and form an image of the grating. apart from this being the single most mind blowing experiment ever to witness I have some questions about the...
  23. B

    Converging Meniscus Lens, Filled with Fluid

    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. Using the result in...
  24. A

    Combination of lens and mirror

    Homework Statement a convex lens forms a real image of a point object at a distance of 50 cm from convex lens. a concave lens is placed 10 cm behind convex lens on image side. on placing a plane mirror on the image side and facing the concave lens it is observed that final image now coincides...
  25. A

    Simple Optics Problem (plane mirror and lens)

    Homework Statement A plane mirror is placed at the origin. A converging lens with a focal length of 5.00m is located at x=12.50m. A object is placed at x=22.5m Find the final location of the image in terms of its X coordinate & magnification. Homework Equations 1/q + 1/p = 1/f (lens)...
  26. M

    Focal length of lens at border of two liquids

    Homework Statement I need to find optical power (reciprocal focal length) of this system with thin lens Homework Equations I tried to solve this using spherical diopter equation n1/a+n2/b=(n2-n1)/R where a is object distance and b is image distance The Attempt at a Solution equation for...
  27. J

    Help please -- convex lens problem and focul length

    Homework Statement Suppose the convex lens is placed at the 49.4 cm mark, and an image forms on the screen at the 70.5 cm mark. Find: A) The focal length of this lens: ____ cm B) the absolute value of the magnification of this lens: ________ C) the height of the image: ________cm Homework...
  28. S

    Calculating Focal Length of 1D Fresnel Lens

    Homework Statement Calculate the focal length of 1D Fresnel lens, whose transmittance is given as $$T(\xi)=\frac 1 2(1+\cos(\alpha \xi ^2)).$$ Homework Equations Anything you wish The Attempt at a Solution I have no idea. I tried to use the equation for diffraction image $$u_p=C\int _0...
  29. E

    Exploring Real & Inverted Images with Bi-Convex Lenses

    Homework Statement An object is placed between the optical centre and the focus point of a bi-convex lens. The image obtained is always inverted and real. Is this statement true? Justify your answer using the thin lens equation. Homework Equations The Attempt at a Solution
  30. S

    Powell Lens Equations for Gaussian to Flat Top Beam Conversion

    I am a Post graduation student and I am doing a project on the conversion of a Gaussian beam into a flat top beam using optical components. I have found that the best component to do the same is a Powell lens. I would like to know more about the equations connecting the input beam diameter...
  31. B

    Question on mirror and lens combinations

    Homework Statement The question is attached in the jpeg file. Homework Equations 1/do + 1/di = 1/f The Attempt at a Solution First reflection : 1/100 + 1/di = 1/80 , di = 400cm ( To the right of the lens ) This means that the image created is a virtual image since it is behind the lens. So...
  32. A

    How can I determine the properties of a thin lens using basic formulas?

    Homework Statement I've tried to attached the image of the diagram. If that isn't working please let me know.Height of incident marginal ray now 25. Assume a thin lens. Find: a. the effective focal length b. the power of the lens c. surface curvature for front and back surfaces (assume...
  33. M

    Determining the focal length of a gradient index lens

    Homework Statement There are three subquestions in this question, all marked bold. Let's consider a gradient index lens of thickness ##d##, whose refractive index changes with the distance from the axis with the following formula $$ n(r) = n_1 + a r^2 $$. Determine the lens's focal length...
  34. maajdl

    SDP.81 : how do we see the gavitational lens?

    I just read this news: http://www.space.com/29042-cosmic-ring-photo-rules-them-all.html I wonder how we can know about the gravitational lens, how can we even be sure it is there? Would that be only by analyzing the image of the supposed distant galaxi? Which kind of analysis? Or are there...
  35. S

    How to Obtain a Magnification of -2 from a Convex Lens?

    Homework Statement You wish to obtain a magnification of -2 from a convex lens of focal length f. The only possible solution is to: A) place a virtual object at a distance 2f/3 from the lens. B) place a virtual object at a distance 5f/3 from the lens. C) place a real object at a distance...
  36. K

    Magnification through a lens at various diameters

    We have a high power plus lens of known front curve, index, and center thickness and have placed a known diameter circular target at a known distance behind the lens. Observing the circular target through the lens we compute the ratio between the diameter of the original circular target behind...
  37. DrewHizzy

    Diverging and Converging lenses in a system

    Homework Statement A)Find the final position of the image (from the object, I assume?) B)Find the size of the final image of the object. Homework Equations 1/f = 1/do + 1/di The Attempt at a Solution 1) Solved first distance: 1/5 - 1/4 = 1/di --> 4/20 - 5/20, di = -20cm 2) Use di1 for do...
  38. B

    Distance from the object to objective lens and focal length

    Homework Statement 1) The medium-power objective lens in a laboratory microscope has a focal length fobjective = 3.70mm . If this lens produces a lateral magnification of -42.5, what is its "working distance"; that is, what is the distance from the object to the objective lens? 2) What is the...
  39. Venerable R

    Double Lens System: Converging/Diverging

    Homework Statement Image: http://i.imgur.com/NMS7BUK.jpg?1 a) Find the position of the final image of the 1.0-cm-tall object. b) Find the size of the final image of the 1.0-cm-tall object. h = 1 cm f1 = 5 cm do = 4 cm f2 = -8 cm L = 12 cm di = ? Homework Equations 1/f = 1/do + 1/diThe...
  40. brianeyes88677

    Understanding the Focal Plan of Parallel Light Through a Thin Lens

    Why does parallel light focus on the focal plan when enters a thin lens at an angle θ? How to proof that mathematically?
  41. J

    Help with radius of curvature and refractive index of lens

    Hi, I am a first time poster and I am completely lost with this question. Any help would be greatly appreciated Filling the space between a contact lens and the cornea is a small quantity of liquid of refractive index of 1.336. Assuming the refractive index of the lens material is 1.490 find...
  42. RaulTheUCSCSlug

    Unraveling the Mystery of Strained Eye Magnification

    Homework Statement This is not really a homework problem but I wanted to figure out how to derive the equation for a strained eye which is $$ M= (N/f) $$ where N is the object distance from the normal near point, and f is the focal length of a magnifying glass. But then, this is for a relaxed...
  43. A

    Need some info about light heat amplified by lens

    It is known that a magnifing glass can start a fire, but I don't fully understand the phenomenon and I have the next questions: - Does the effect depend on the shape and the material of the lens you use? - Where can I find some details about heat produced by light or particulary on this...
  44. R

    Divergine Lens Embedded within Converging Lens

    Homework Statement A thin converging lens made of glass (##n_g=1.55##) happens to have an inclusion of water (##n_w=1.33##) at the center. The lens surfaces have radii of curvature ##R_{out} = r_1=r_2=10m##, and the water inclusion has the shape of a diverging lens with radii of curvature...
  45. Phynos

    Location of object that forms an image in 2 lens system

    Homework Statement Two converging lenses having focal lengths of f1 = 12.5 cm and f2 = 19.5 cm are placed a distance d = 49.0 cm apart as shown in the figure below. The image due to light passing through both lenses is to be located between the lenses at the position x = 33.0 cm indicated. (a)...
  46. W

    Will UV Filter Stop Bullseye Glass From Starting Fires?

    Practical question: Will placing a clear UV filter over a magnifying lens inhibit the ability of that lens to focus sunlight to the degree necessary to produce fire? I have a window with several "bullseye glass" panels in my home and have noticed that when the bright winter sun passes through...
  47. Robsta

    Calculate focal length of lens by diffraction.

    Homework Statement A collimated beam from a white-light source is incident normally on a transmission grating with 500 lines per mm. The transmitted light then passes through a lens which is used to project the visible (380–780 nm) spectrum of the light source on to a strip of photographic film...
  48. Z

    Lens Question for Design of an Infrared Spotlight

    Hello All. I'm working on a project to build an infrared spotlight which will hopefully light up a distant object so that I can see it on an IP enabled night vision camera. The lens problem seems very straight forward, but I could use some help. Per the attached diagram, I want to focus the...
  49. S

    Would you -- drawing of wood blocks and a ruler to measure a lens

    < Mentor Note -- thread moved to HH from the technical physics forums, so no HH Template is shown. Also, thread title edited to make it more descriptive. > The question is asking me to draw a diagram to show how, in the laboratory you would use two rectangular blocks of wood and a metre rule...
  50. Prashasti

    Finding Focus Length in Broken Double Convex Lens

    Homework Statement A thin double convex lens of focal length f is broken down into two halves at the axis. The two haves are then combined, as shown in the figure. What will be the focal length for the arrangements...
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