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. W

    Understanding Image Formation: Exploring the Role of Photons and Detectors

    General question regarding how images are formed. As you move your eye "detector" around a illuminated room. The is image of let's say "a book" is in every position in the room at a given time correct--even before you "look" at it? The photons reflected off the book have formed an image of the...
  2. Arman777

    Optics: deriving Nodal and Principal Points for a thick lens

    Homework Statement I have to derive the Nodal and Principle points distance equations. Homework Equations Equations can be found here http://scienceworld.wolfram.com/physics/ThickLensFormula.html The Attempt at a Solution I have no clue about how to approach this problem. If...
  3. Arman777

    Deriving the Thick Lens Equation: How to Obtain the Equations for a Thick Lens?

    Homework Statement Derive the equations for the thick lens and obtain, ##\frac {1} {f}=\frac {n_L-n'} {nR_2}-\frac {n_L-n} {nR_1}-\frac {(n_L-n)(n_L-n')} {nn_L}\frac {t} {R_1R_2}## Homework Equations ##n## is the medium where light ray enters, ##n_L## is the medium of the lens and...
  4. Hydrous Caperilla

    Simple microscope and convex lens

    When does a convex lens behhave as a simple microscope and what are the conditions for the object and the lens to act if there are any?Is the magnifying power of microscope fixed beyond which it will act as a regular convex lens
  5. K

    Is the Ideal Lens Calculation Patentable?

    I have patent pending on this. I am publishing despite that. Patents last 20 years at the most, plus it can be researched already. I choose a focal point. I dirve rays from it in a fan fashion toward lens, which for now is in shape of mere segment. The segment has its position in horizontal...
  6. N

    Plano-convex lens, which side should face the laser source

    I have two measurement cases in my setup. An divergating laser beam (not an gaussian) is measured at two locations from lens , at nearby i.e. 400 mm, and far away, > 2000 mm away. My lens is an plano-convex lens. Which side should face the laser in these two cases? I know that the...
  7. HastiM

    Does the picture change if we turn a thin lens around

    Hello, suppose we are given a thin lens and consider an image of some object formed by that lens. I am wondering what would happen to the image if the thin lens is flipped around (180 degrees)? Of course, if the lens is perfectly symmetric -like for a bi-konvex lens- then the picture should not...
  8. HastiM

    Principal plane of a thin lens

    Hello, in geometric optics people usually say that the refraction of light beams due to a thin lens can be handled by introducing a hypothetical plane (the so called principal plane) at which all the refraction can be considered to happen. But most books only picture the situation for symmetric...
  9. Phil123

    [LENS] Given focal length and height, find object distance

    Homework Statement An object is in front of a convex mirror. We then obtain an erect image whose height is equal to 25% of the height of the object. What is the distance between the object and the mirror if we know that the focal distance is equal to 0.2m? Homework Equations M = Yi/Yo = q/p...
  10. T

    Wave Physics - Optics - Effective Focal Length

    So we have the focal lengths: f1, f2, ..., f7 = 25mm And the distance between the lenses: d1-2, d2-3, ..., d6-7 = 50mm I have figured out that if the system would be afocal if it had an even number of these lenses. This is because the focal length of two adjacent lenses is the same as the...
  11. H

    Estimating the FOV of a thin sliced plano-convex cylindrical lens

    I've scoured the internet, books I have available, and forums, but I can't seem to find any information regarding the field of view of a plano-convex cylindrical lens. The lens in question would be a 1/4" slice from something like a 26x13mm lens. The dimensions would then become 6.35x13mm...
  12. C

    Optics: Focusing Explained with an Owl

    I've made a drawing of what is confusing me here. 1. This should be a case of focusing into infinity or not? 2. Can anyone explain what happens with the owl?
  13. S

    Optical Can a DIY Fresnel Lens Concentrator be Created Using a Rotating Liquid Mold?

    Just running an idea for a diy fresnel lens past .. [ In the context that parabolic mirrors have been created by rotating a liquid ] The volume left above the parabola is also parabolic, so ...if that volume is used as a mold for casting it should form a reasonable solid lens, at least for...
  14. PeppaPig

    Image distance from the hemisphere lens

    Homework Statement As shown in the figure, the distance between the object and hemisphere lens is R0. The hemisphere lens radius is R0. Find the distance between the image and the flat side of the lens if observing from the curved side of the lens. Refractive index of glass and air are n and...
  15. N

    Height of the image of Jupiter created by the objective lens

    Homework Statement I have the following variables: f = .93 m f(e) (eyepiece) = .0082 m distance toJupiter pj = 588 E^9 diameter of Jupiter dj = 139822 E^3 Find the height of the image of Jupiter created by the objective lens of a telescope. Homework Equations M = -q/p q = f Where M is the...
  16. P

    Focal Length given M and distance between obj and img

    Homework Statement The distance between an object and its upright image is 28.0 cm. If the magnification is 0.550, what is the focal length of the lens that is being used to form the image? Homework Equations 1/f = 1/so + 1/si M= -si/so The Attempt at a Solution See included image...
  17. HastiM

    Image if a mirror is placed at the focal distance of a biconvex lens

    Hello, suppose we are given a biconvex lens with focal length of 4 cm. Further, an arrow of height 1 cm is placed in front of the lens in a distance of 8 cm (i.e. twice the focal length). Lastly, a mirror is placed on the other side of the lens at a distance of 4 cm and such that it performs an...
  18. W

    Understanding Two Convex Lenses: Ray Diagram and Focal Lengths

    Homework Statement I'm supposed to make a ray diagram of two convex lenses when light initially hits the first lens at parallel rays. When f(total) goes to infinity, the distance between the two lenses = the sum of the focal lengths of each lens. Homework Equations The Attempt at a Solution...
  19. T

    Constant thickness lens varying refractive index

    Homework Statement Homework EquationsThe Attempt at a Solution my initial approach was to just imagine the light rays leaving the focal point and emerging parrallel but then the result had no dependence on thickness how to tackle this problem how does the thickness even factor in
  20. Asmaa Mohammad

    Medical The power of the human eye's lens

    Hello, I read in my physiology book that when the ciliary muscle relaxes, the power of the eye lens decreases, hence we get the ability to see far objects. I am new to physiology, and when I googled "the power of the eye lens" I didn't find articles explain the sentence above simply. So I...
  21. T

    What do polarisation lens block?

    Electromagnetic waves are created by a accelerating charge that induces a changing electric field, that induces a changing magnetic field which propagates together through space. The electric and magnetic field are at right angles to each other. Polarisation blocks all but one plane of the...
  22. Sophrosyne

    Medical Optical transparency of the human cornea and lens

    There are two optically transparent tissues in the human body: the cornea and the lens. But how they achieve this transparency is different, and both in turn appear to achieve this differently than in other optically clear materials like glass. The transmission of light through glass or other...
  23. Const@ntine

    Lens & Reflector: Final Idol (Optics)

    Homework Statement...
  24. M

    What is the max magnification of 0.5mm film lens.

    What is the max magnification of 0.5mm film lens. Film is just on the top of flat object(Paper, Display, Picture, etc). If Fresnel lens is made on top of the film, Can I magnify the object? Thank you.
  25. Q

    Creating a two lens system of tunable focal length

    Hello, I would like to reduce the beam size of a laser by a factor of 10, with the purpose of replacing a long (750 mm) lens with a more compact design. Ideally I'd make a Galilean lens pair where the ratio of the focal lengths are 10:1 to produce a small collimated beam. However, I think I...
  26. G

    Lens engineering for virtual reality

    What type of lens/prism would be needed to allow a image sensor to see 180 degrees, so the sensor could see a hemisphere. It doesn't matter if the input is distorted. I thought that a glass pyramid with a square base might work.
  27. A

    B Black Hole Gravitational Lens: Bending Light & Mass

    https://en.wikipedia.org/wiki/Gravitational_lens I want to know about bending light property of a black hole. The bending angle formula does not tell that r is perpendicular distance to light. Does a black hole having mass M has different bending power than the body having the same mass M...
  28. izMuted

    How do I know if the image is real or virtual?

    Homework Statement I know that the object distance is 15 using the equation m = - (v/u) (+ or - depending on real / virtual) 2 = (+ or -) 30/u u = 15 However how do I know if the image is real or virtual? Homework Equations m = - (v/u) The Attempt at a Solution
  29. S

    Optics: Half Lens in the Air, Half Lens in Water.

    Homework Statement Hello everybody! One surface of a biconvex lens (n=1,5) is in the air (na=1) while the other surface is dipped in the water (nw=4/3). If the power of the lens in the air is Po=10 Dioptri, The lens power in such condition is? Homework Equations Lensmaker Equation...
  30. G

    Image is inverted when I look into a projector lens -- Why?

    I'm using a film projector as an editor, meaning I run the film slowly and use a low power bulb. I want to minimise any possibility of damaging the films. To view a film I simply look straight into the lens – and I see an inverted image. What I can't explain is why the projected image appears...
  31. S

    Converging lens solve for all variables given f, Hi, and Ho

    Homework Statement [/B] What is directly given in the problem: Converging lens with f=1.43m Hi = 2m Homework Equations Hi/Ho = di/do M = Hi/Ho = di/do 1/f = 1/do + 1/di The Attempt at a Solution Ho = 2m * 20 = 40m Not sure how I can get do from this. All of the equations seem to need di.
  32. C

    Is the equivalent lens of two such that f_1+f_2<h divergent?

    The focal of the lens equivalent of two thin lens at distance h is $$1/f=1/f_1+1/f_2+h/(f_1 f_2)$$ Therefore, supposing that ##f_1>0## and ##f_2>0## (both lenses are convergent), if ##f_1+f_2 <h## then the equivalent lens should be divergent. Nevertheless consider the example in picture...
  33. C

    Ray diagram diverging lens both object and image virtual

    Homework Statement Draw the ray diagram of the case of a diverging lens where both object and image are virtual, that is ##f<0## , ##p<0## with ##p<f## Homework EquationsThe Attempt at a Solution I did not find this particular case of ray diagram in any textbook so I would like to know where...
  34. G

    Compound Microscope: Calculating Image Location with Two Lenses

    Homework Statement A compound microscope consists of two converging lenses (the objective and the eyepiece) placed 7.0 cm apart. If the objective has a focal length of 2.8 mm and the eyepiece has a focal length of 3.3 cm, what would be the location of the final image of an object placed 3.0 mm...
  35. N

    Image FFT and Lens MTF: Evaluating Final Image Quality

    Hi, I am trying to determine the final image on a detector having a 600x600 mm viewed object and the known MTF of a lens. So when I FFT the object, thus creating frequencies -128/600 : 128/600 for a 256x256 image, how does the multiplication of the transformed object and the MTF "keep track" of...
  36. CCR5

    Geometric Optics and Lens Power

    Homework Statement A farsighted boy has a near point at 2.3 m and requires eyeglasses to correct his vision. Corrective lenses are available in increments in power of 0.25 diopters. The eyeglasses should have lenses of the lowest power for which the near point is no further than 25 cm. The...
  37. H

    Combined lens & mirror system

    Homework Statement The object in the figure below is midway between the lens and the mirror, which are separated by a distance d = 24.9 cm. The magnitude of the mirror's radius of curvature is 20.4 cm, and the lens has a focal length of -16.5 cm. (a) Considering only the light that leaves the...
  38. Marcus95

    Biconvex Lens Floating on Mercury

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

    Lenses and Pinholes: What Does "In Focus" Mean? - Comments

    stevendaryl submitted a new PF Insights post Lenses and Pinholes: What Does "In Focus" Mean? Continue reading the Original PF Insights Post.
  40. I

    Finding the optical power of a contact lens

    Homework Statement A farsighted man uses eyeglasses with a refractive power of 2.05 diopters. Wearing the glasses 0.020 m from his eyes, he is able to read books held no closer than 0.265 m from his eyes. He would like a prescription for contact lenses to serve the same purpose. What is the...
  41. Antraxius

    Designing a planocovex PMMA lens

    As an electrical engineer, I am an amateur on optics, but I really could use some help. I am making a lens of PMMA, 2D. To 'convert' a rotary movement into a sweep. The lens needs to be 120mm long, with its focus at a max distance of 80mm the light traveling out of the lens needs to be parallel...
  42. Charles Link

    The Diffraction Limited Spot Size with Perfect Focusing - Comments

    Charles Link submitted a new PF Insights post The Diffraction Limited Spot Size with Perfect Focusing Continue reading the Original PF Insights Post.
  43. Z

    A Description of imaging through lens using quantized EM field

    Usually the imaging through lens is described using geometrical optics or wave optics. However, I wish to study some imaging processes through lens where the light intensity is at the single photon level, under which condition I think the correct description should use a quantized...
  44. Biker

    Thin lens approximation and Apparent depth

    So we are studying optics in school this semster, Very interseting topic I say but I just have a couple of question I want to ask. In concave and convex mirror, we study spherical ones where F = R/2. I was able to prove this and that it is only an approximation when ## R >> h_o ## or ## h_0##...
  45. H

    Optical System Creation: Maximizing Image Quality with First Surface Mirrors

    Hi guys, I have one question or maybe some questions about creation an optical system. I have a drawing of the system (see below) where are placed 2 right angle prisms. The aim of this is to reflect image from "A" to "B". I suppose that I will need to add some lenses to do it right without...
  46. Toby_phys

    Compound lens separated by a distance

    Homework Statement Homework Equations We will call ##s## the distance of the object from the first lens, ##s'## the distance of the image from the first lens and ##s''## the distance of the image from the second lens. The Gauss's lens equation: $$\frac{1}{s} +\frac{1}{s'}=\frac{1}{f_1}$$...
  47. heavystray

    Invisibility cloaking using 4 lenses

    Hello, So, here's an article about invisibility cloaking http://www.businessinsider.my/how-to-make-a-rochester-invisibility-cloak-2014-9/?r=US&IR=T#ruDbxWBJYWXsXcyW.97 What I don't understand is how's the object between the lenses is cloaked. Is it because the rays are focused to a point...
  48. G

    I Steam punk, Field of view including the eye

    Sorry if I missed the answer in my search. I expect I'm not use the correct terms. I want to design a Galilean/opera glasses style steampunk monical mounted to my reading glasses. I already have a simple lens that I can swing in front of my one eye. When using commercial eyeglass mounted...
  49. R

    Experimentally finding focal length of small biconvex lens?

    I have fabricated a few biconvex lens (12mm diameter) for an experiment and am trying to find their focal lengths. My though is to set up three parallel lasers and find where the beams converge. However, even with the smallest laser diodes I could find, three beams surpass the diameter of the...
  50. T

    Experiment: Measuring the focal length of a converging lens

    Homework Statement You are required to set up a light source, an object grid, a converging lens and a screen so that a quantitative investigation of object and image distances can be performed. Tabulate corresponding object and image distances (p and p' respectively). Also tabulate values of...
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