# Lens Definition and 833 Threads

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. ### I Question about two interference patterns viewed at infinity

Hello, It seems like we use two different set of hypotheses to consider that we are at infinity in optics and I would like to know which one is correct. In the case of Young's interference experiment we can see the interference pattern at infinity when a<<D and x,y<<D, with "a" the distance...

3. ### I Two or more gravitational lenses perfectly aligned with Earth?

Has anyone ever discovered 2 or more gravitational lenses perfectly aligned with earth? So one lens magnifies the galaxies behind it and another lens between the first and earth magnifies it even more? Would you even be able to tell if they were?
4. ### GRIN Lens - Gradient Coefficient Expression

z= the length of the lens, P is the pitch and g is the gradient constant. I attempted to solve for g using the radius and delta, but I think I am missing a key function. The units of g should be 1/mm. P=0.23 delta = 0.05 nmax = 1.6 nmin = 1.6 - 0.05 = 1.55 r = 1.0 mm z = (2*pi/g) * p Attempt...
5. ### B How to Troubleshoot a Lens Focusing Issue with a DIY DSLR Lens

Hello all As an experiment I tried to make a lens for my dslr with plastic lens of a Kodak Funsaver disposable camera. The lens in this camera is convex-concave and is a 30 mm lens. Problem is: My lens can only show items in focus if they are at about 1-2 cm away from it. Nothing past 2 cm...
6. ### A Question about detector and lens

Light from the sample is collimated light. For imaging, does the spectrometer requires a lens to focus the collimated light on the entrance slits of the detector. Using the beam splitter, the collimated light from the sample is directed toward the spectrometer. Previously, we used a lens to...
7. ### Finding the focal length of a converging lens with VERY limited info

This is the solution but I do not understand??? How could they just assume the object distance equals 2f? No magnification is given here. We know the candle produces a real image and the distance is limited, so that means it must be somewhere between the principal focus, the center of curvature...
8. ### B Understanding Corrective Lenses: Examining Reversed Prescriptions

My girlfriend has started wearing corrective lenses to address some nearsightedness and I'm not fully understanding what she's going through, or what the difference is for her with and without glasses. I was curious if you basically reversed the prescription of the lenses, would it take my...
9. ### Calculate a radius of a circle on a screen

The picture is here. The radius should be ##R=2.94\,\mathrm {cm}##. In the original solution, it is solved by using a critical angle ϵm. The b is the maximum distance at which a beam can refract. I understand this solution and an image of it is here: But I wanted to calculate it by knowing...
10. ### What is a focal length of a thin convex lens?

I think that there might be several solutions. I drawed one possible situation: I think that this is just geometry, but I don't know how to solve it simply. I had an idea that if the beam was going through the black axis, then it would be easy to calculate, and that would be aslo solution for...
11. ### Calculating Chromatic Aberration

Since the lens is convex, I figured that the points where the red and blue light focus on the optical axis would be equal to their respective focal lengths (f), given that the incoming rays are parallel to each other and perpendicular to the lens. Solving this got me to 1/fred = (1.52 -...
12. ### B Prism Camera Lens: Expanding Visible Light Spectrum?

Is it possible to create a lens that expands a narrow range within the visible light spectrum to represent it using full visible spectrum?
13. ### I Light Refraction, Biconvex Lens, Diagram Help

I've read that the refraction of light at the boundary of a medium can be described as follows: -a line of connected people marching. one side of the line enters mud, and slows down. This causes the non-mud side to pivot towards the slower side, which then causes the line to change direction...
14. ### How to Solve IGCSE Lens q with Unspecified Distance

I know a sketch diagram is required for the question but they haven't specified the distance from the beam to the lens. They've just given the height of the beam. So how do I know how far I should place the object? Should the object (beam) be at infinity?
15. ### Find pupil locations w/ paraxial ray tracing (thick lens, Geary CH 5)

Per the description given in the book, one can trace rays FROM the physical aperture stop into object space to find the size and location of the entrance pupil (EP). Also, one can trace rays FROM the physical aperture stop into image space to find the size and location of the exit pupil (XP). In...
16. ### I Image appears outside of q -- Lens Maker's Equation confusion

Summary: Does the image distance q in the lens-maker's equation mean where real images form or where any image at all forms? If the former, what separates the real image from all other reflections? Hi all, I attached a series of images taken with a camera for a concave mirror, the Pasco...
17. ### What is the Focal Length of a Lens for a Perfectly Fitting Image on a Sensor?

My attempt: m=-v/u=-f/(-f-u) -1/0.5= -f/-f-0.10 -> -f-0.10=0.5f -> f=0.20 m
18. ### I Using simple lenses to image AFM Probes

Hello, Using a CCD camera and simple lenses, the probe of the cantilever and its surroundings are to be imaged. Since the cantilever is 50 um wide and some of the surroundings are to be imaged, the optimal image magnification is from 4 to 8. I therefore used a convex lens with a focal length of...
19. ### I Huge farsightedness/nearsightedness lens

Hello guys, I have a question for optics experts, is there any possibility to produce a farsightedness/nearsightedness lens in big dimmensions, without distorting the obsjects or anything else you watch through that lens. Thank you!
20. ### Photovoltaic vs. thermal radiator Solar Panel comparison (using a lens)

Hi, Has anyone experience with photovoltaic solar panels and thermal radiator type solar panels? 1/ How do they compare when both have the same collection area? If the thermal radiator was much smaller than the collection area, and a lens the size of the collection area was used, focused on...
21. ### Splitting Rock with Superficial Heat

Hi. I'm an amateur mason - I currently use drills and plugs to split granite boulders. I've used sledge hammers, chisels and levers. I've dropped rocks, used hydraulic presses and tended fires to crumble and split rock. It's hard work. It's long hour work. I'm wondering if there's not a better...
22. ### Image position and magnification for underwater spherical lens

Using the data given and recalling that in this configuration ##R<0## I get: ##\frac{1.33}{0.5}+\frac{1.5}{q}=\frac{1.5-1.33}{-0.2}\Rightarrow q\approx -0.427 m=-42.7 cm## so the image is virtual and is ##42.7\ cm## to the left of vertex ##V##. The magnification is ##M=\frac{n_1 q}{n_2...
23. ### I Lens angle of coverage/image circle

Hello, I was wondering what parameters determine the angle of coverage/size of the image circle of a lens. For example, for a fixed focal length, aperture and flange focal distance of a camera, what can a lens designer do to change the size of the image circle. I'd also like to know how the...
24. ### B Infrared Cameras -- Do they use a Lens to Focus?

Can infrared cameras focus IR radiation as a visible light camera focuses visible light? I think IR doesn't pass through glass well? What are these germanium lens about? I don't think my Flir IR camera has a lens.
25. ### Lens Calculations using Refractive Index

Answer: I already found the answer for Sin theta 2 like the pic below But, I am still not sure about how to derive delta here. Can anyone show me they way? thank you
26. ### I Applications of Virtual objects

I've heard virtual objects are used in cinema halls I'm not sure of what that means, can someone explain this to me please? And btw by virtual object i mean when diverging rays from real object passes through a convex lens, the rays will converging and if you'll place a plane mirror infront of...
27. ### I Lost Aspheric Lens Design Equation Found

Hi all, I was interested in ideal shapes for lenses and Google popped up this very old thread: "Mathematical shape for a lens with no spherical aberration"A member named Redbelly98 replied (<link>) with a now-broken link to a Thorlabs page that gave an aspheric lens equation. Took a minute...
28. ### I Finding focal length of the lens using "u-v" method

I was just checking out this experiment for finding focal length of a lens that I did few years back. the method used was called as the u-v method(https://www.concepts-of-physics.com/pdf/uv-method.pdf), and here in this method, object distance u and image distance v is measured from the sharp...
29. ### I Help Needed for Lens Selection for Fiber optics

I am using a fiber optic cable through which led light propogate, fiber's half acceptance agle is 30 degree. I want to make the light (diverging)comes out of fiber into collimated beam and this collimated beam will pass through filters, sample and will be used for Fluoroscence application. hope...
30. ### A Spherical aberration in Biconvex lens

I was recently looking for proven relations between focal length, radius of curvature, refractive index etc of a convex lens as I was working on an experiment, I did Find a relation, between Height from principal axis and focal length, and it was a huge relation!I did the experiment to verify...
31. ### Michelson Interferometer with a lens

Hello everyone, i have a homework but I'm so confused how to solved it , can someone make a solution manual for this homework?, Thankyou.
32. ### B Is there a material that allows visible light and UV light to pass through?

Is there a material that allows visible light and uv light to pass through? Edit: A physical material
33. ### I Shorten the lens distance while having same focal length?

Hello Everybody, I'm David from Spain, and happy to be here. We have a LED that needs a FL50mm collimator which is focused to infinite, because we want parallel rays. So the lens is at a distance 50mm (approx) from the led. However, 50mm is too much distance for our design, so the question is...

Hi PF I've been twice to the dentist recently, and I've taken this picture. I don't find it in Google, and I know nothing about optics, but some words that appear at the textbook I'm now studying seem to be related: concavity, reflection, parabole...In few words, I'm more concerned about this...
35. ### I What Lens to Put In Front of an Complex Lens to Push Focal Plane Back?

I have an extremely fast (f/1.05) night vision optic that I scavenged from a old night vision unit which is faster than current production lenses (f/1.23). However due to the design of newer night vision tubes, the lens will not focus to infinity on the night vision tube. This is because the old...
36. ### A Heisenberg lens and probabilities

Hi Pf in her experiment Birgit Dopfer uses an https://www.researchgate.net/figure/color-online-The-Dopfer-experiment-of-the-Zeilinger-Group-Innsbruck-If-detector-D2-is_fig7_265787833 the distance between the source and the lens is 2f and the detector may be at the distance f or 2f behind the...
37. ### Position of the principal points of a telephoto lens system

Hi everyone, for a lab I need to determine the position of the cardinal points of a telephoto lens. The focal points were determined experimentally, and the focal length given on the lens is 200mm. The principal points should be determined with f=PF. In all the textbooks, the principal points...
38. ### Lens with different refraction index on each side

So I am not really familiar with lens questions when there's 2 different refraction indexes. I tried using n1/p+n2/q=-(n2-n1)/R but it doesn't seem to work. p would be the actual location of the fly and q would be the virtual location, what the fish sees if I am understanding correctly. n1...
39. ### Calculating the Effects of Lens Closeness on Light Refraction

I know what happens initially, calculated as follows. 1/∞ ＋ 1/q = 1/50, q=50 1/-25 + 1/q = 1/-25, q= ∞ However, how do we know about the after when the two lenses get closer to each other?
40. ### Combination of thin lens and concave mirror

I created the following ray diagram to help me solve the problem: Then I applied the mirror equation 3 separate times. However, the final image distance I got is wrong. I'm wondering if I'm mistaken in taking the last object distance to be negative. However I only have one more try to get this...
41. ### Why 0.3m From Lens Is Optimal Focus?

Apparently, it must be placed at the focus (0.3m away from the lens). Why is this so?
42. ### Approximating the Edge of a Lens as a Prism

Hello there, for part a. of this problem I thought I should try to find the radius of curvature R of the lens using the Lensmaker's Formula. Then it would be quite easy to find the minimum thickness T by just finding the thickness of the circle segment using Pythagoras' Theorem. But part of...
43. ### Lensmaker's equation when the 2 mediums on both sides of the lens are different

Hi, I chanced upon an interesting diagram lately, and was wondering what the lensmakers equation for such a lens would be. Attached below is the diagram. Basically, the refractive indexes of the 2 mediums surrounding each side of the lens are different. They have also calculated the focal...
44. ### How to find the focal length of a lens (Problem with a task)

Hello. I need formulas for the focal length of a lens when I have refractive indices of two centers and two radii of curvature of spherical surfaces or one radius of curvature of spherical surfaces. I search the internet but can't find it.
45. ### Invisible Ink that you can see through an IR lens

I’m making an eyepiece that can see hidden messages, and I need to know an ink that you’ll be able to see through the IR lens.
46. ### The magnetic field just above a lens in an electron microscope

I'm looking for an estimation or simulation of the magnetic field in the horizontal plane just above a typical lens in a transmission electron microscope. A rough cross section of such a lens can be seen here: electron lens - Bing images . The lens is cylindrically symmetric around the vertical...
47. ### Correction of horizontal astigmatism in an anamorphic lens

Hello, I need advice which lens should I use for correction of horizontal astigmatism in anamorphics lens which contains two prisms. Focal length which I need to be focused is about 3 meters. I am using this prisms pair with projector. When I display grid horizontal lines are not focused...
48. ### 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...
49. ### Lens selection for close proximity surface photos

Good day all, I am searching for some advice on how I could successfully take photos of a surface that is 5mm away from a CMOS camera sensor. My ideas so far are; 1.) Find a lens with sub millimeter focal length (0.2mm by my calculations) 2.) Utilize mirrors to increase object distance 3.) Pin...
50. ### Why does a divergent lens create an interference pattern?

I used a green laser pointer (λ = 532nm). I aimed it at a divergent lens that has a focus of -50cm. The distance from the laser does not play a big role. As a result, a very clear interference pattern with a series of concentric circles appeared on the screen. I did not find a suitable...