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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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Calculating focal length for wide angle conversion lens [closed]

How do you calculate the focal length for a wide-angle conversion lens, say with a factor of 0.7, that would convert a 50 mm lens to a 35 mm lens, e.g. for photography. Such a lens should be a concave ...
StanW's user avatar
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Principal plane of the lens [closed]

I want to set up an optical system as shown in the figure. A laser beam passes through a diffraction grating, then a beam splitter, through a 35mm focal length lens to the object, and then is ...
Yuu's user avatar
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Eye Floaters Optics

Eye floaters are these annoying objects floating in someones eye, usually seen by someone experiencing them as squiggly lines and dots buzzing around, either dark or partially transparent (I ...
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Exit Pupil, Objective Aperture, Magnification, and Brightness

Why is it that for two pairs of binoculars, with equal aperture, the one with smaller magnification has larger exit pupil and results in brighter images? If I understand correctly, the aperture ...
guilhermemp's user avatar
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2 answers
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Optical projector that reduces image size

I'm starting to wonder if this is not possible. I have built a projector to project UV light, through a monochromatic mask [a black & white 2x2 film negative] onto a target. The image on the film ...
Inventorgeorge's user avatar
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What is the function of a concave lens in a laser pointer?

In my cheap laser pointer I found a concave lens in front of the LED. I expected a convex lens. If I remove the concave lens the beam is much less collimated. The same if I replace the concave lens ...
flappix's user avatar
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Intuitively understanding virtual images in a multi-(thin)lens system

Let's say there is a multi-lens system of a converging lens (ex. a biconvex) and then a diverging lens with an object on the left of the system. And furthermore, let's say that due to the specific ...
Entangled Being's user avatar
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Can we see real images with lens? [duplicate]

There was this question. In an experiment to determine the focal length of a convex lens, a student obtained a sharp inverted image of a distant tree on the screen behind the lens. She then removed ...
Kanak Sohane's user avatar
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How to Calculate Focal Length when in another medium?

How do you calculate the focal length of a lens when it is placed into another medium, if I only have the focal length of a lens in the air? I understand that the lensmaker's equation should be used, ...
Astrovis's user avatar
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Is image projection a good test quality for hyperopia glasses?

I've just bought a new pair of glasses for hyperopia, and want to test the lens quality. If I use the lenses just like a magnifying glass, to project the image of a lamp onto a wall, the image should ...
Rodrigo's user avatar
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2 votes
3 answers
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What is the apparent location of a real image formed by a lens? [duplicate]

Let's say I place a tennis ball 1 m in front of a plane mirror. The mirror will form a virtual image of the tennis ball, and if I look in the mirror, it appears to me that there is a tennis ball ...
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Best High Zoom Lens Configurations [closed]

Just wondering which lens configurations are usually best or most optimal for achieving high zoom in the smallest space or with fewest lenses. E.g Let's say we want to achieve a 1000x magnification. ...
user94863's user avatar
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What is a convex-concave lens?

I came across this term while studying for optics, and I'm unsure as to what this means. My thinking is that it might be a meniscus lens, but the text separately give two different models for each ...
Astrovis's user avatar
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2 answers
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Spherical aberration of lens

Why is spherical aberration absent in an image formed by a plano-convex lens on its principal axis? Will it be present in other types of lenses?
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How to find the image field of a Gaussian beam impinging on a positive lens? I am trying to calculate the impulse response and find the image field

How to get the image field for the setup in the following question , where a Gaussian beam is incident on a positive lens with focal length f z0 and z1 are the object and image distance? Can anyone ...
condensedvaddi's user avatar
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Why is a bigger camera sensor better at low light than a smaller one?

People say a bigger camera sensor is better for light performance as the photo sensors are bigger and hence let in more light. But couldn't you just let the same light in and focus it down onto the ...
George kirby's user avatar
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Lens maker’s formula from parabolic approximation

I’m attempting to derive the lens maker’s formula for a thin or thick lens using the parabolic approximation. I’m familiar with the other proof using the law of refraction and different angles. The ...
TheorVHP's user avatar
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Formula for power of a lens submerged in a medium

I was always of the opinion that the power of a lens would invariably be the reciprocal of its focal length, irrespective of the medium surrounding it. However, I ran into a slightly different formula ...
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Real image drawn in case of concave mirror is bit off

About I am trying to draw real image of object in front of concave mirror. Case is when object is lying on the Center of curvature. What I have done so far There are two rays A ray incident on the ...
Pankaj's user avatar
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Where is the final image located at in a compound microscope?

In a compound microscope, is there a standard as to where the final image should be located? After doing some research, I arrived at either the final image should be located at infinity (to be focused ...
Astrovis's user avatar
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How to find out the relation between liquid lens curvature and changing the focal point? [duplicate]

I have a question regarding liquid lens. how much we have to change the curvature to get an image shift of 30mm?
Marjan Shojaei's user avatar
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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 ...
Max Wang'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 ...
user94863's user avatar
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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
1 answer
201 views

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 ...
DisD's user avatar
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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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1 answer
89 views

Visibility of objects when looking through a half-covered concave lens [duplicate]

If a concave lens is half-covered with a piece of a paper and used to look at an object, is the object completely visible or is part of the object not visible? (The person who closed this question ...
Johnny's user avatar
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2 answers
59 views

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
3 votes
1 answer
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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
4 votes
1 answer
143 views

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 ...
tush's user avatar
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1 answer
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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
1 vote
1 answer
590 views

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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37 views

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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1 answer
84 views

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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1 answer
39 views

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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1 vote
2 answers
431 views

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
1 vote
2 answers
95 views

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 ...
drevoksi's user avatar
1 vote
0 answers
42 views

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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0 answers
77 views

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
1 vote
2 answers
62 views

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
2 votes
0 answers
45 views

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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3 votes
1 answer
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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
158 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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-1 votes
1 answer
61 views

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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0 answers
30 views

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 ...
Shinnaaan's user avatar
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0 answers
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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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