Questions tagged [lenses]

A lens is a transmissive optical device that focuses or disperses a light beam by means of refraction.

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How do you derive the formula's for equivalent focal length and back principle plane for 2 thin lenses separated by a distance?

I've found online that the formula for the effective focal length of 2 lenses separated by a distance is: $$ \frac 1f=\frac 1{f_1}+\frac 1{f_2}-\frac d{f_1f_2}. $$ However, I'd like to know how this ...
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Why does Lens made of Two Materials form only Two Images?

I was solving a test this morning and came across this question. Now by intuition, I know that there should be only two images formed. Rays shall converge through the upper section of the lens to form ...
Schrödinger's Cat's user avatar
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Very basic questions about sign convention in mirrors [closed]

According to the sign convention objects are placed to the left of a spherical mirror so the object distance is always negative. However when in a question we say the object distance is $x$ then how ...
koiboi's user avatar
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Is it possible to define the Point Spread Function for a lens?

I have seen several papers and reports in which the Point Spread Function (PSF) of a microscope is calculated and measured. In particular, as far as I understand, a light point source is placed in the ...
Marco Gandolfi's user avatar
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Multiple lens configuration thickness and distances

Struggling to understand where I should measure lens thickness and distance between lenses from. I've attached an example multiple lens setup. For determining individual lenses thickness is it simply ...
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Printing 2d fresnel zone plate

Recently my teacher asked me to create a Fresnel zone plate (Fresnel lens to be accurate). I wanted to print it using a laser printer with a resolution of 1200*1200 dpi. I know that i should block ...
Mohammad Ali Shojaie's user avatar
2 votes
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Lenses and missing reflection

I am wondering why reflected rays are not considered with lenses. If a ray strikes a surface, another is reflected off that striking point; however, this is not added when studying lenses, only ...
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What are the equations for a 2D projection of the distortion induced by a cylindrical lens?

Imagine you have a cylindrical lens of power $C$ and of angle $\theta$ relative to some neutral 0 axis. I want to know, if you took a normal 2D image and shown it through that lens, what would the ...
Stan Shunpike's user avatar
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Final image formation in these 2 cases:

Can someone please explain simply how we determine how many times we have to consider reflection and refraction to obtain final image. Example a: Here they only considered refraction twice to obtain ...
Alex Aboda's user avatar
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If a concave lense is covered half with a piece of paper and is used to look at an object, is the object completely visible? [duplicate]

If a concave lense is covered half with a piece of a paper and used to look at an object, is the object completely visible or is some part of the object not visible?
Johnny's user avatar
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Why isn't the image always formed at the focus?

if a parallel ray falls on a convex lens and a converges at the focus on the other side of the convex lens then for every position of the object shouldnt the image be formed at the focus?
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Using Fermat's principle to derive the Cartesian paraboloid

I am self-studying Optics by Pedrotti and I'm on the subject of geometric optics, specifically ideal Cartesian surfaces. These are reflecting or refracting surfaces that form perfect images. I was ...
nwsteg's user avatar
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Geometric optics multiple lens focal length calculation

Just wanted to understand how I would go about calculating the effective focal length of these different lens configurations. There's the combined focal length formula, but I'm struggling to apply it ...
user94863's user avatar
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Why is there no "parabolic abberation" in lenses?

I am trying to understand what an "ideal" lens would look like. Spherical surfaces are not correct, as these produce spherical aberration. This article here, is really useful. It 'derives' ...
AccidentalTaylorExpansion's user avatar
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About the focal length and $f\#$ of spectrometers

Suppose I image light into the entrance slit of a spectrometer (actually a monochromator). The spectrometer is schematically shown below. On the spectrometer's specs sheet, it is said that it has a ...
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How would a lens mirror work?

Say you have a convex lens with one of the sides completely coated with a mirror like substance, effectively rendering one side into a mirror. How would this lens work? Would the usual formulas like $\...
WilliamHarvey's user avatar
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What is the use of $4f$ lens system for imaging?

Almost all the imaging experiments use $4f$ lens combination for imaging. What I don't understand is what is there a need for this combination. From my understanding, we can just use a convex lens. ...
QuantumOscillator's user avatar
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Why does focal length of a concave mirror $f=-R/2$?

When both the distances $R$ and $f$ are measured from mirror only they shouldn't be of sm sign? When we take it negative in mirror formula that I understood... But why here I'm confused
Pranjal Bajaj's user avatar
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What shape should the lens be so that it collects all the rays at one point?

I want to understand what shape a biconvex lens should be so that it collects all the rays at one point (without spherical aberration). So I want to get the equation of the lens shape depending on the ...
Mikhail's user avatar
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Magnification of closely packed thin lenses, or of closely packed lens and mirror

I was taught how to calculate the equivalent foci in both the cases. And since the formulae resemble the simple mirror and lens maker formulae, teacher said that this system is behaving like a single ...
Gautam's user avatar
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How does 2f-2f lens configuration work?

Say I want to image a shape which is cut out on an Aluminium sheet. If I am passing a laser through the object in a setup like the image below. What I don't understand is why is there a need of ...
QuantumOscillator's user avatar
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Do biconvex lenses... actually focus parallel light onto a single point?

Everywhere I read online, it is said that biconvex lenses have two spherical surfaces, focusing parallel light onto a single focal point. Now, consider a solid sphere, made out of glass. It must be a ...
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OPTICS - How to achieve "infinity projection"?

I'm trying to learn a little bit more about how huds in military planes are able to get their info projected onto "infinity" (whatever distance is enough, like 10 meters or so??) so that ...
Satamanster's user avatar
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Silvering of lenses and their focal length

For a silvered biconvex lens the equivalent power is give by $P_{eqv.}=P_{lens}+P_{mirror}+P_{lens}$. Here we put power of lens as negative since it behaves as a concave mirror overall. Reasoning for ...
Physics Kota's user avatar
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Conflicting lensmaker's equation representation

I keep finding these two conflicting forms of the lensmaker's equation. I understand that (n2-n1)/n1 is the same as (n-1) if referring to a lens in air, but I can not make sense of why the reciprical ...
Saveer Jain's user avatar
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Why doesn't a lens after a diffraction grating affect the optical path difference?

When observing interference fringes one often uses a lens after the diffraction grating to focus the fringes on a screen like this: At first sight, one might think that after the lens the path ...
Julia's user avatar
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Can a system of lenses or compound lens have a higher numerical aperture than a single element in the system?

I am attempting to create a simple Abbe condenser for a microscope, which typically consists of two converging lenses. Ideally, I would like to achieve a numerical aperture for the condenser of ...
Yashka Oreza's user avatar
2 votes
1 answer
109 views

Should power of lens be dimensionless quantity?

My book defines the power of lens using this way: The power P of a lens is defined as the tangent of the angle by which it converges or diverges a beam of light falling at unit distant from the ...
Razz's user avatar
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When does magnification not depend on distance of object? [closed]

Two thin lenses share a common optical axis. Their focal lengths are f1 = 20 cm, respectively and f2=50 cm. In front of the first lens at distance x>f1 there is an item. On the screen behind the ...
mathchad's user avatar
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Is it preferable to say $v$ is " image distance " than to say " image position " in spherical mirror formula?

I was going through spherical mirror formula $1/v + 1/u = 1/f$ where $u$, $v$ and $f$ are named as object distance, image distance and focal length respectively. But while using this equation we do ...
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Super resolution with STED microscopy and evanescent waves?

Consider the angular spectrum method, given a field $U$ with a wavelength $\lambda$ we can decompose it with Fourier transform. \begin{equation} U(x, y,0) = \int \int {\tilde{U}_0(f_x,f_y)} e^{2 \pi ...
MementoMori's user avatar
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Plano convex lens refraction angles formula

I am designing an optical device with several plano-convex lenses. In order to determine several measurements I need to be able to calculate the resulting refracted angles at the edges of the lens in ...
Birger Evansson's user avatar
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Imaging and illumination plane in microscope

I've been delving into the intricacies of achieving Kohler illumination in microscopy, and the term 'illumination and image-forming rays' consistently surfaces. Most resources emphasize the ...
CoffeeBiscuit's user avatar
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As we all know a convex lens doesn't exactly converge all rays parallel to it's axis on a single point. So I want to find one such figure

Writing a differential equation for such a figure is an uncomplicated task. It can be accomplished by using snell's law. But the resulting equation probably isn't solvable. I put it in wolfram alpha ...
Arpan Bajpai's user avatar
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109 views

Why do projector condenser lenses focus light directly onto the projection lens?

I've seen diagrams for projectors where condenser lenses focus light directly onto the pupil of the projector lens, after going through the image source. Am I misunderstanding the diagram? If not, ...
Sohil Sathe's user avatar
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Out-of-focus color in reflective microscopy with Köhler EPI-illumination

It is well known that Köhler illuminator in optical microscopy is designed in a way to ensure uniform illumination of the field, often with adjustable apertures to allow as little light as possible to ...
BarsMonster's user avatar
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Image point in Lensmakers' equation proof makes no sense?

I've attached an image that describes the light-rays refracted through a thin lens. P' represents the first real image that is created when light is refracted through the first convex mirror. But how ...
Emil Sriram's user avatar
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1 answer
158 views

Use of sign convention two times in ray optics

In this particular derivation of refraction happening at a spherical surface in terms of its radius of curvature , image and object distance and refractive index is done by my book as shown When we ...
Razz's user avatar
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What lens(es) do I need to form an image from incoming parallell rays?

Let's say that I have a source of parallel light rays (e.g. from a laser and a beam expander). I pass that light through a volume that contains some particles. Particles at different locations and ...
Tor's user avatar
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Maximum numerical aperture and diffraction limit of a lens

In this thesis, you can read page 62/63 the following: "The lens is designed for λ = 780 nm and works diffraction limited up to NA= 0.55. However the diffraction-limited numerical aperture for λ =...
DarkBulle's user avatar
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Is Huygens' Law satisfied in the following case?

I have a GRIN lens with the refractive index varying linearly with y, and supposedly this lens tilts the wavefront. Since the rays are travelling normally in both refractive index materials, they ...
Shivansh Jaiswal's user avatar
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Varifocal glasses [closed]

I hope this isn't the completely wrong community for my question, please let me know. I did search for 'varifocal' and got some hits, it seems (still getting used to these glasses, so it is a bit hard ...
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PBR: Why conductors have tinted specular?

So, as I know when light beam falls on some surface it reflect (specular) and refract (diffuse). Refracted part will interact with material's molecules and it can lose all energy or fly back out of ...
Anaph's user avatar
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Is the lens image, a combination of diffraction patterns?

As I was reading through Luigi Picasso's Lectures in QM, I came across this paragraph where he explains the reason behind the resolution power of the optical instruments. He writes: Let us now ...
Rice Field's user avatar
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Optics: How does lens prescription work for near vs. far distance?

I don't have any physics background aside from intro physics so apologies if my question sounds very shallow. If lens power is based on focal length, but our eyes adjust its focal length based on the ...
natrium's user avatar
1 vote
2 answers
105 views

Telescope Equation: wrong understanding?

It's well known that the basic formula for the angular magnification of an optical telescope is $$ |M| = \frac{f_{ob}}{f_{oc}} $$ where $f_{ob}$ is the focal length of the objective, and $f_{oc}$ is ...
Fat32's user avatar
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Why would an object disappear when switching from monocular to binocular vision?

I have just used a compound binocular microscope which has an ‘eyepiece graticule’ (ruler in arbitrary units) in the right eyepiece lens. If you close your left eye (or occlude the left lens), the ...
user265902's user avatar
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Location of optical centre in Lens

The simple definition of optical center for a convex or concave lens was given as point through which a ray passing suffers no deviation from its path, but is there any geometrical location of this ...
Shridp's user avatar
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Is it possible to make real DIY microscope with several lens?

I have alot of small double convex 7 mm lenses and i have very small lens 4mm And i have plano concave lenses all of them is small I tried to combining them to get a magnified image and it worked when ...
Pcp115's user avatar
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Trouble simulating/ray tracing a simple microscope

I'm trying to run a (seemingly) simple simulation of a basic microscope using the free software WinLens 3D Basic, but the ray tracing looks wrong: The microscope consists of a small plano-convex lens ...
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