What is Concave lens: Definition and 25 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. T

    Negative Concave Lens - Creating a Beam Expander

    I am trying to create a beam expander. I purchased 3 double convex and 3 double concave lens (200mm, 300mm and 500mm). But for the diverging concave lens I need a negative -500mm lens. What exactly is a negative concave lens? I am unable to find anything on amazon or any other site that has a...
  2. physics-james

    Can you make a more focused beam by using convex and concave lens?

    When you put a convex and then concave lens in front of a light source, the light will be parallel but narrower than when it came in such as in a laser beam expander/compressor. Using a pen laser and a convex and concave lens, is it possible to focus the beam by putting a convex then a concave...
  3. Rheegeaux22

    Help With a Difficult Lenses Question: Find the Answer!

    Homework Statement The question is : https://postimg.org/image/lntyejfvp/ Homework Equations 1/s +1s' =1/f The Attempt at a Solution Hello, I have an upcoming test on Monday on lenses and while reviewing I've come across a question that confused me. My understanding is that the image of...
  4. TheCapacitor

    Finding focal point of concave lens using concave and convex

    Homework Statement [/B] I was doing http://stao.ca/VLresources/sci-tie-data/lessons/1400_1499/DivergingLensExperimentDeta.pdf experiment. Let's look at this image: Suppose we get the imaginary object at dv by convergence lens. And this object is like a real object for the concave lens. Then...
  5. P

    5 Questions dealing with Optics, image included

    1. A real inverted image I of an object O is formed by a certain lens (not shown); the object—image separation is d = 40.0 cm, measured along the central axis of the lens. The image is just half the size of the object, a. What kind of lens must be used to produce this image? b. How far from the...
  6. C

    Determining a specific frequency to make the ball bounce

    So, here's the set-up: A small stereo speaker is connected to a function generator. A concave lens, bearing a ball is place over the speaker. Now, the frequency is slowly increased in the function generator. My question is, Will the ball really bounce at a certain frequency? Because I am not...
  7. 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...
  8. F

    Second focal point of a concave lens

    Why is the focal point to the left of a concave lens called the second focal point? Isn't it just a matter of the name? So can't the focal point on the left of the lens be called F1 instead of F2?
  9. D

    MHB Convex and concave lens and paraxial rays

    What effect would a convex (concave) lens have on paraxial rays? For a convex lens, the rays would pass through and converge on the focus on the other side. For a concave lens, the rays would reflect back to the focus on the same side. Is this correct?
  10. K

    Real 3D Image produced by concave lens

    Homework Statement Find the correct image produced by the concave lens. F is focal length. Homework Equations If an object is placed between F and 2F, the image will be inverted, real, larger and beyond 2F. The Attempt at a Solution I choose the answer A. Is it correct? *Please...
  11. C

    Does the focal length of a concave lens change in a different medium?

    My question is as follows: Does the focal length of a concave lens change when put into a medium such as water? Initially the focal length of the lens is 20 cm in air. Would it get larger or small in water?
  12. 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...
  13. C

    Concave Lens _ Image Formation

    A concave lens always forms a virtual image (for a real object), will it always form a real image for a virtual object? (that is, when rays converge on it) If yes, why? If no, why?
  14. I

    Solving the Concave Lens Problem for a Hotel Room Peephole

    A certain 0.86 cm lens is used in a peephole for hotel room doors for safety reasons. The tenant sees the maid in the peephole but she is reduced in size by a factor 0.01. A. What type of lens must be used? B. Where is the image of the maid located? C. What is the power of this lens...
  15. G

    Calculating the Volume of a Concave Lens Using Multiple Integration

    Homework Statement A circular concave lens of radius 2 units, has two refracting surfaces described by z=1/2(x2+y2+1) and z=-1/2(x2+y2) What is the volume of the glass? Homework Equations Over a region R: V=\int\int\int dA The Attempt at a Solution I have no idea how to start...
  16. 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...
  17. 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...
  18. 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...
  19. A

    Focal length of concave lens experiment

    Is there any way to find rough focal length of concave lens and convex mirror without using convex lens? Though I did the experiments(with object and image needles, not candle) very carefully with no parallax errors during my practical class, my readings are incorrect. I want to know if der s...
  20. W

    Draw Double Concave Lens Diagram

    Homework Statement "Please draw an image for a double concave lens with the object paced between the lens and the focal point. Remember to show all the required rays, their direction, and the focal point of your lens" Homework Equations no equations needed. The Attempt at a...
  21. J

    Find the focal length of a concave lens using a convex lens?

    Can anyone explain to me the procedure that one would follow to you find the focal length of a concave lens using a convex lens? Thanks.
  22. J

    Solve Concave Lens Problem: Step-by-Step Guide

    Homework Statement http://img215.imageshack.us/img215/8457/physicsol4.jpg Homework Equations n1sin01=n2sin02 1/f = (n-1)(1/r1-1/r2) The Attempt at a Solution I'm really jus confused with this problem I don't really see where to start. I'm assuming the fish bowl is a...
  23. B

    Solving Final Image Formed from Convex and Concave Lens

    Homework Statement An object is placed 6 metres from a convex lens of focal length 30cm. A concave lens of focal length 5cm is then placed 20 cm from the concave lens, on the side distant from the object. Determine the position, magnification and nature of the final image formed (to solve...
  24. Amith2006

    Is the Image Formed by a Concave Lens Real or Virtual?

    # A convergent beam is incident on a concave lens as shown in figure. Which of the following is not correct? a) The image formed is real b) The image formed is virtual c) The image formed is erect d) The image formed is magnified I solved it in the following way: Let f be the focal...
  25. Amith2006

    Focal length of concave lens using convex lens

    # A convex lens of focal length 10 cm forms a real image of an object placed at a distance of 20 cm from it. Midway between the convex lens and the position of the image a thin concave lens is introduced. The image formed now is at a distance of 5 cm away from the earlier position. What is the...