What is Lenses: Definition and 320 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. S

    Finding Focal Lengths of Microscope Lenses

    Can someone tell me what sort of equation I would use for this question, I can't use the magnification as I have two unknowns. At least I don't know how to apply the magnification equation to this question. A microscope is made in a tube 25.0cm long. It magnifies 5.00 x 10 to the 2 times...
  2. M

    Light, Mirrors, Lenses, immediate help required

    Hello, here is the problem i am having trouble with. The sun falls on a concave mirror and forms an image 3 cm from the mirror. If an object 24mm high is placed 12 cm from the mirror, where will its image be formed? So far, i have decided that since 1/f = 1/do + 1/di... 1/f = 1/do + 1/3 =...
  3. B

    Lenses: If given object height and focal length, is it possible to calculate

    the image's height? If so, how? I have the formulas, but see no way of making a substitution. If you wanted to know the problem, it states: The focal length of a camera is 35 mm and the radius of the moon is 1.74 x 106 m. Calculate the diameter of the moon's image that appears on the...
  4. K

    Optics - Glass lenses in other mediums

    Glass lenses behave in the way it is expected to behave when the medium they are in is a vacuum or air. But if the medium is also glass it obviously doesn’t work as a lens. If the density of the medium is higher than that of glass the lens works in the opposite way. The power of a lens...
  5. R

    Lenses, diminished and magnified

    This is probably a stupidly easy question, but I'm confused so I need to ask about it. :smile: I have this experiment I was doing where I have a light source at one end (which is enclosed in a casing and only let's light get out in the shape of an arrow because of an arrow shaped hole) and...
  6. S

    Calculating Refractive Power of Two Lenses Combination

    hey- I've been working on this one for quite some time now and just can't seem to get it: Two converging lenses with focal lengths 10 cm and 20 cm are placed 30 cm apart. Rays from a very distant object are impinged on the lens system parallel to the principal axis. What is the refractive...
  7. S

    Question:How to Draw Ray Diagrams for Diverging Lenses

    Hi i have a question about a lens,im not sure if this is the right place to ask but il ask anyways...please help I am really stuck! Question: An object is placed 24cm infront of a concave mirror of focal length 18cm. Where is the image formed and what is its magnification?Include an...
  8. S

    An object and two lenses - Is this right?

    ok have a look at the pdiagram i drew the thing in the middle is a convex thin lens and to the right is a concave mirror. The arrow on the left stands for the object, the object is placed at 2F1. The convex lens to cancave mirro length is 2(f1 + f2) Find the location of the nature and...
  9. R

    Is Moisture Harmful to Telescope Lenses in Cold Weather?

    i just bought a telescope and i am in Canada it iz really cold outside and i want to take it outside to look at the stars but someone told me that moisture would get stuck in the lens and it would be ruined can somebody tell me if this is true personally i don't think it would but i don't want...
  10. B

    Mirrors and lenses under water

    I just have 2 questions. If you use a mirror under water would the focal length change? And same question, but if you use a lens under water would the focal length change? I was thinking, light rays travel slower in water, so then it difracts away from the normal more than if it was in...
  11. JasonRox

    Humidity and Lenses: What to Do When Too Much Dust in House

    In my area, humidity is where it's at. One of the problems I noticed when grabing my mirror (first time using it) to pack up was the fact that it soaked up enough water that I can't even see myself in it. This explains why it didn't work. I DID NOT WIPE THE LENSES. I just put the...
  12. O

    Calculating Focal Length Using Sign Conventions for Lenses

    Okay for the most part I understand the concepts involved but I'm having some trouble with this question. The distance between an object and its upright image is 20.0 cm. If the magnification is 0.500, what is the focal length of the lens that is being used to form the image? Now...
  13. N

    How Is the Focal Length Determined When an Object and Its Image Coincide?

    An object pin is placed 20cm in front of a convex lens which is 10 cm away from a plane mirror . An inverted image is found at the same position of the object(above the object). What is the focal length? thanks
  14. A

    Find Object Position for Upright and 4x Sized Image | Concave Mirror Formula

    Stumped...lol.. A concave mirror has a focal length of 62.4 cm. Determine the object position for which the resulting image is upright and four times the size of the object. What formula do I use for this question? :confused:
  15. D

    Infared light - lenses and ink

    is it possible to read infared ink with human eyes. I have seen lenses for cameras but can't find anything for eyes. If so, where is informaiton on this thakns
  16. C

    Effect of Partial Covering on Lenses and Mirrors

    It's a known fact that when you partially cover a lens (with fabric or something), the image on the other side would look less illuminated, since less light rays go through the lens. However, what happens when you partially cover a concave/convex mirror? Our teacher thinks the same thing...
  17. S

    Why do light rays continue to bend towards the center after exiting a convex lens?

    Hi, I know that when entering a convex lens, light rays bend towards the center due to refraction. But why do they keep bending towards the center once they exit the lens? Should'nt they now bend away from the lens because they are going from a denser to a rarer medium? Thanks SK
  18. R

    Solving the Problem of Converging Lenses' Focal Point

    I am having trouble with my homework. I know the answer but I can't figure out how to get there. The question is "An image of a flower is produced on a screen by a lens 1.60m from the screen. The image of the flower has a linear magnification of -2.5. What is the focal point of the lens?" I...
  19. R

    Converging and diverging lenses

    Hello, I am reading over the topic of converging and diverging lenses, and I had a question relating to phenomena of image formation as seen through these. Based on the ray diagrams that are typically used (freshman physics) how does one conclude whehter or not an image is inverted or...
  20. X

    Help with A-level physics coursework. focal lengths of lenses

    hi! im in a bit of a panic at the moment i have 2 days to complete my physics coursework on focal lengths. the title is: "you are given two convergin lenses of different lengths. you are to devise an experiment:- -to measure the focal length of each lense -to measure the focal...
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