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. P

    Concave Mirror Lens Ray Diagram

    Homework Statement A person 1.62 m tall wants to be able to see her full image in a plane. a) What must be the minimum height of the mirror? b) How far above the floor should it be placed, assuming that the top of the person's head is 15 cm above her eye level? Draw a ray diagram...
  2. P

    What is the Unknown Distance in a Lens Equation Problem?

    Homework Statement http://img368.imageshack.us/img368/9489/physicszv8.jpg Homework Equations (1/f) = (1/p) + (1/q) The Attempt at a Solution I tried solving this but I don't know what the original P was so I can't solve for q. How can I solve this?
  3. P

    Solve Plano-Convex Lens Lensmaker's Equation

    Can someone help me with the Lensmaker's equation for a plano-convex lens? The formula for a bi-convex lens is readily available but it includes a term for the radius for each of the two curves. A plano-convex lens has only one radius!
  4. I

    Can a lens act as a quantum eraser?

    I am just starting to study quantum mechanics, so I realize I am working with over-simplified examples, but that should work out since I'm hoping for simple answers... Among other things, the claim that this eraser would work has me scratching my head...
  5. L

    Understanding the Thin Lens Equation: How to Graph and Interpret Results

    I need to learn how to graph do=1/(f -1/di) like i have my measurements and when i plug in my di i get a do so what do i do with my old do?
  6. L

    How Do Similar Triangles Derive the Thin Lens Equation?

    kk so i found out the steps involved deriving the thin lens equation, but what i don't get is when you have 2 similar triangles say triangle abd,edf are congruent how does the 2 triangles make it so its di/f-1. so what I am basically asking is can someone thourougly explain to me what's going on...
  7. L

    Deriving the Thin Lens Formula: How Does Equation 1 Relate to the Triangles?

    Hi I need help on figuring where and how 1/f = 1/do + 1/di My teacher told me it relates to the ray diagram but i have no clue where to start to find where this formula has come from. Any help would be much appreciated.
  8. P

    Lens Problem, Help from Anyone Thank you, I appreciate it very much

    [SOLVED] Lens Problem, Help from Anyone! Thank you, I appreciate it very much! Homework Statement An object is placed 30 mm in front of a lens. An image of the object is located 90 mm behind the lens. a) What is the focal length of the lens? b) On an axis (the x-axis) draw the lens at...
  9. F

    Optics, lens problem pleaase help

    Optics, lens problem pleaase help :) 1. Two converging lenses, the first with focal length 40 cm and the second with focal length 33 1/3 cm, are separated by 10.0 cm. An object of height 6.0 cm is placed 20.0 cm in front of the first lens. What are the size and orientation of the final image...
  10. R

    Optics - What is the magnification of the lens?

    Object O1 is 15.0 cm to the left of a converging lens of 10.0-cm focal length. A second lens is positioned 10.0 cm to the right of the first lens and is observed to form a final image at the position of the original object O1. (a) What is the focal length of the second lens? (b) What is the...
  11. Z

    Solving Refraction Puzzles: Coin Depth & Convex Lens Image

    Problem 1: A thin hollow glass sphere has a radius of 1 m. A coin is placed at the bottom of the glass sphere. 2.09 metre cube of a liquid of refractive index 1.5 is poured into the glass shpere. A person is viewing the object vertically. What is the apparent depth of the coin? Im not sure...
  12. J

    How i can find the magnification of a lens?

    how i can find the magnification of a lens?? how i can find the magnification of a lens if i don't know it's focal length??
  13. D

    Graphically interpreting data regarding magnification with a convex lens

    Homework Statement How do I find the relationship of magnification to the graph of "Object Distance vs. Image Distance" or the graph of "Inverse Object Distance vs. Inverse Image Distance" for data points collected from a light box and a convex lens? Basically for the lab I used a light...
  14. D

    Does the Refractive Index of a Lens Affect its Focal Length?

    I just have one question regarding the focal length of a lens. I had a test today and there was a fill in the blank section regarding how the focal length of a lens is determined (there was two empty spaces.) Wouldn't there be three possible answers. The curve of the lens, the index of...
  15. T

    Lens Optics: Converging Lenses Question

    Homework Statement Two converging lenses, the first with focal length 40 cm and the second with focal length 33 1/3 cm, are separated by 10.0 cm. An object of height 6.0 cm is placed 20.0 cm in front of the first lens. What are the size and orientation of the final image? A. 6.0 cm...
  16. S

    Locating Object and Image with Converging Lens

    Homework Statement A converging lens with a focal length of 6.00 cm forms an image of a 4.00 mm tall real object that is to the left of the lens. The image is 1.24 cm tall and erect. Where is the object located? (Give the object distance using the correct sign.) wrong check mark cm (to the...
  17. L

    Finding Focal Length of Diverging Lens with Parallel Rays

    Homework Statement I'm trying to find the focal length of the diverging lens. The converging lens is 24cm behind a diverging lens. The focal length of the converging lens is 31cm. I know that parallel light strikes the diverging lens and then affter passing through the converging lens the...
  18. E

    Medical Contact Lens Safety: Are They Dangerous for Eyes?

    are contact lenses dangerous for eyes? i hate glasses. another question is that is there any contact lenses which are colored and also do glasses job too?
  19. N

    Thin lens equation for diverging lenses.

    Hi, I was reading a section which explains about the "thin lens equation for diverging lenses" and it included an example; Formula: 1/f = 1/di + 1/do where f is the focal distance, di is the distance of the image from the center and, do is the distance of the object from the center. Example: f...
  20. N

    Does anybody know where to get Converging lens ?

    Does anybody know where to get "Converging lens"? Hi, I work on an independent study course for physics and it requires converging lens in order to begin the experiment. I thought of going to a local optical stores and asking them for purchase but I don't think the Business Depot guys...
  21. R

    Position Barlow Lens for 3x Image w/ Focal Length -0.05m

    1. I am trying to figure out a problem involving a barlow lens in a telescope. All I know is that the focal length of the lens is -0.05m. I want to know where to place the barlow lens in front of the image created by the first lens (as if the barlow wasnt there) in order to get an image 3x the...
  22. B

    Converging lens magnification

    If I have a converging lens, of focal length f, and magnification of the image m, where q is the distance of the image from the lens show that q = (1+m) f m = - q/p 1/f = 1/p + 1/q I just need to show that they are equal, but I am getting confused with the maths.. q= (1 - (q/p))...
  23. J

    Thin Lens Equation - Hypothesis

    Homework Statement Hi, I am writing a lab report, and I have no idea how to come up with a fitting hypothesis for this lab Purpose: To determine the relationship among the focal length, the image distance, and the object distance of a converging lens.
  24. F

    How far is the lens from the slide if the image is virtual?

    Homework Statement A transparent photographic slide is placed in front of a converging lens with a focal length of 2.44 cm. The lens forms an image of the slide 13.2 cm from the slide. How far is the lens from the slide if the image is virtual? nearer possible distance = Homework...
  25. G

    What Lens Power Does a 77-Year-Old Need to Correct Near-Sightedness?

    A 77 year old man has a near point of 115 cm. What power lens (in diopters) does the man need in order to be able to see an object clearly at the normal near point of 25 cm? Assume that the man will get contact lenses, that is neglect the two centimeters that glasses would be away from the eye...
  26. E

    What is a good lens holder material

    I am just wondering what is a good material or a material i should look for when choosing to make for the lens holder. From my detector to the lens (focal length), does it need like a non-absorbing or non reflective material? When a manufacturer sells the complete camera set (regular camera)...
  27. G

    Focal Length of Diverging Lens: Negative Value Confirmed?

    Can someone confirm that the focal length of a diverging lens is always negative in value? Regards
  28. C

    Fresnel lens with focusing light

    Hi, I'm in a bit of a dilemma, where my limited knowledge of optics has failed me. Here's the scenario: I have acquired a large Fresnel lens (34" x 45"), as used in rear projection TVs. My Dad and I built a frame on which the lens was mounted. Supports have also been installed diagonally to...
  29. A

    Can I Build a Simple Optical Device with Just Two Magnifying Glasses?

    Everyone in our class needs to build a lens optical device such as a projector, camera, copier, telescope, microscope, solar cooker, etc. We will need to include a ray tracing diagram. Has anyone ever made a simple device with lenses? What do you think will be the easiest and cheapest? Thanks
  30. S

    How Do You Calculate the Focal Lengths of Microscope Lenses?

    Homework Statement A microscope is made in a tube 25.0 cm long. It magnifies 5.00 x 10to the 2 times, 50.0 times by the objective lens and 10.0 times by the eyepiece. What are the focal lengths of the two lenses? Homework Equations m= H/h=-q/p q= p(f) / p-f H= -h(q/p) The...
  31. himanshu121

    Digicam Cybershot DSC W80 lens jammed

    Hi everyone I recently bought a digicam Cybershot DSC W80 from india, currently I am in The Netherlands, Actually the problem is when I pressed the button to view the images of which I have taken photograph, my camera get jammed , only thing coming on display is SONY and nothing else even the...
  32. T

    Solve Convex Lens Question: Find Focal Length & Magnification

    An object and a screen are fixed at a distance of 80cm apart and a convex lens forms a real image of the object on the screen. When the lens is moved along its axis a distance of 16cm, a real image of the object is again formed on the screen. Find the focal length of the lens and the...
  33. J

    Understanding Light and Lens Problems in Physics

    Damn light & lens problems :( The problems come from a homework that I've already submitted. I got some right and some wrong, but the ones that I did correctly I'm not too confident in method (which including guessing at times). There's really not really a lot of calculations involved in...
  34. S

    Newton's Rings and plano-convez lens

    Homework Statement A plano-convez lens (flat on one side, convez on the other) rests with its curved side on a flat glass surface. The lens is illuminated from above by light of wavelength 521 nm. A dark spot is observed at the centre, surrounded by 15 concentric dark rings (with bright rings...
  35. 7

    Lens Formula Derivation: Why is the Image Distance in a Converging Lens f(n+1)?

    I recently took a test on lenses. One of the questions was "The image formed by a converging lens is real and is n times the size of the object. If the focal length of the lens is f, the distance from the lens to the image is? Now, the answer is f(n+1) but I can't seem to figure out why...
  36. W

    Forming a Sharp Image with a Lens: Focal Length Explored

    Homework Statement An object and a screen are separated by 20 cm. A convex lens is placed between them, 5 cm from the object. In this position it causes a sharp image of the object to form on the screen. What is the focal length of the lens? The Attempt at a Solution wouldn't it just...
  37. S

    How Is Angular Width Calculated in Lens Optics?

    Homework Statement A converging lens with a 50.0 mm focal length is used to focus an image of a very distant scene onto a flat screen 37.0 mm wide. What is the angular width of the scene included in the image on the screen? Homework Equations The Attempt at a Solution Basically...
  38. M

    Optimizing Telescope Lens Distance for Distant and Nearby Objects

    A telescope has lenses with focal lengths f1 = +25.7 cm and f2 = +5.5 cm. (a) What distance between the two lenses will allow the telescope to focus on an infinitely distant object and produce an infinitely distant image? (b) What distance between the lenses will allow the telescope to focus...
  39. A

    Understanding Diverging Lenses: Homework Statement and Solution Attempt

    Homework Statement How do you know this? if anyone can help, it would be greatly appeciated! Homework Equations The Attempt at a Solution Homework Statement Homework Equations The Attempt at a Solution
  40. D

    Finding Distance Between Lens Positions: Solve for a

    Homework Statement The distance between an object and its image is fixed at 40.0 cm. A converging lens of focal length f = 4.2 cm forms a sharp image for two positions of the lens. What is the distance a between these two positions? Homework Equations 1/p + 1/q = 1/f The Attempt at...
  41. L

    Lens Experiment: Understanding b Values

    I need a little help with a laboratory class I had about lens. Experiment: We had a light source with a draw of an arrow on it, this light go through a lens of +100 mm (focal length) and a surface on the other side of the lens were we can see the arrow on it. We put the light source at...
  42. M

    What Does t Represent in Interference Without a Lens?

    Homework Statement A source S of monochromatic light and a detector D are both located in air a distance of h above a horizontal plane sheet of glass, and are separated by a horizontal distance of x. Waves reaching D directly from S interfere with waves that reflect off the glass. The...
  43. D

    Find Largest Focal Length Lens for Photo of Poster - 2.79mm

    Homework Statement You take a picture of a poster on the wall of a room and maximum distance you can get from the picture is 3.1 m. The poster is 0.8 m wide and 1.2 m tall and you want it to fit in the 24 x 36 mm frame of the film in your camera. What is the largest focal length lens that...
  44. F

    Exploring Converging Lens & Fourier Transform of Aperture

    Hello, does anyone know how a converging lens forms the Fourier transform of an aperture when the obs. screen is at distance=f? If each point emits a spherical wave, the lens should make it then parallel and the FT should be the interference resulting from that. However, if we decompose...
  45. 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...
  46. A

    Cleaning a Cloudy Patch Inside Orion 120mm Telescope Lens

    I own an Orion 120mm f\5 600mm telescope . I bought it last year from Orion . I recently noticed a cloudy patch about 2in. round on the inside of the scope on the lens , it looks like condensation to me . I've always been careful when i bring the scope in the house fron the nights cold air and...
  47. S

    Image Formed by Diverging Lens

    Homework Statement 2. An object is placed two focal lengths from a diverging lens. What type of image forms? What is the magnification? Where is the image? Homework Equations 1/f = (n-1)(1/r1-1/r2) The Attempt at a Solution a) Virtual Image b) m = 1 c) the image is on...
  48. B

    Thin Lens Equation - How to Solve for the Position of a Converging Lens

    Homework Statement 3. A converging lens has a focal length of 10 cm. A screen is placed 30 cm from an object. Where should the lens be placed, in relation to the object, to produce a focused image?Homework Equations 1/do + 1/di = 1fThe Attempt at a Solution Do can not be greater than 2F...
  49. R

    Can anyone tell me where to buy an off-axis collimating lens?

    I'm tired of looking for mirrors to do my applications, so I was wondering if anyone knows where to find an off-axis collimating lens. I haven't been able to find one myself, not even in edmund optics or other major suppliers. If anyone does know, can you tell me where to get it and the place...
  50. J

    Reason for Different Focus Distances in Converging Lens Lab

    we used a converging lens and a screen with white paper in front of a window to form an image of a distant tree outside. This was about 15cm. When we used an optics bench and a candle to figure out the focus, it was 16.3cm... What would be a reason for the difference in the number?
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