Questions tagged [lenses]

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1answer
58 views

validity of plane waves in thin lens approximation

If you have radiation emitting at the focus of a lens, why is it that on the other side of the lens, rays are essentially parallel within a region $\approx \frac{D^2}{\lambda}$ , where D is the ...
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1answer
168 views

How do those cheap shoebox-phone projectors throw any “decent” image?

You've probably seen them; shoebox phone projectors. They throw a very dim image, but I'm surprised it throws any image at all, since the lightsource is completely diffuse. Why does it still ...
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0answers
188 views

Finding a Lens System Matrix for a Planar Concave Thick Lens

How can I go about determining the lens system matrix for a planar concave thick lens? I analyzed that a light ray first enters the lens and refracts, then it goes through the lens, and then it ...
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2answers
242 views

Why do things seem smaller when seen through spectacles?

When I see through someone's spectacles, things seem very small to me? Why does it happen? Do people wearing spectacles see things smaller than we do?
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1answer
76 views

Combination of lens

In the above diagram, let the refractive index of concave lens be $n_1$ and of convex be $n_2$.So in order to apply lens maker formulae for it, will I have to assume air separation between the lens? ...
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1answer
320 views

Why is eye accommodation necessary?

Why is eye accommodation necessary when infinite number of light rays come from a specific point of an object and we can use any pair of rays we need and the curvature of the lens need not to be ...
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0answers
2k views

Sign convention in lenses and mirrors [closed]

Can we change the sign convention (distance measured in the direction of incident ray positive and opposite negative) midway solving a problem. According to me we should ,as the mirror/lens formula is ...
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0answers
158 views

Location of lens having effective focal length

We know a/c to Gullstrand's equation that the effective focal length of two lenses separated by a distance $d$ is given as $$1/feq=1/f1+1/f2-d/f1f2,$$ but the equation doesn't clarify on the position ...
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2answers
790 views

Does the position of the final image in a multiple lens system found by the thin lens formula always agree with the ray diagrams?

For example, in the figure given below let the object be at O, the eye of the observer at E and the pole of the convex and concave lenses be P and P' respectively. Assume the object is placed such ...
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1answer
496 views

How is it possible that a converging lens can form a virtual image if its function is to make the light converges?

If the function of a converging lens is to do the light converge, how it can form a virtual image, which as far as I know is formed when the light diverges ? I have another question, that may seems ...
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1answer
434 views

Imaging fidelity in a 4F setup

In Fourier optics, a 4$f$ setup is an arrangement of 4 lenses like so: The idea is that the beam waist $\omega_f$ at the last position (at $x = 2f_1 + 2f_2$) is equal to the waist $\omega_i$ at x = 0 ...
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1answer
446 views

Focusing LED using a Fresnel lens at different distances

Simple setup: A Red LED in front of a small fresnel loupe/lens (credit card size). Using a screw I can adjust the distance between the LED and the lens. The LED is centered with regard to the lens. ...
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1answer
60 views

How can I make a Telescope with the lenses I have

List of lenses I have Convex - 200mm F.L - 50mm Dia Convex - 50mm F.L - 50mm Dia Convex - 40mm F.L - 40mm Dia Convex - 45mm F.L - 25mm Dia Concave - 200mm F.L - 50mm Di I tried to make a ...
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1answer
492 views

Where does the last term come from in the two-lens formula: $\frac{1}{f}=\frac{1}{f_1} +\frac{1}{f_2} -\frac{d}{f_1f_2}$?

I can derive the formula for lenses in contact: i.e, $$\frac{1}{f}=\frac{1}{f_1} +\frac{1}{f_2}.\tag{1}$$ But for two lenses separated by a distance $d$ I can't seem to get: $$\frac{1}{f}=\frac{1}{...
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1answer
57 views

Why would an additional filter element destroy a lens's focus?

We are testing an infrared camera, which produces images fine across a reasonable range of wavelengths. Now we want to see what images we get at certain specific wavelengths. So we (naively) acquired ...
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1answer
80 views

Is there any limit to extent of magnification?

I want to know if there exists some mathematical limits to what extent we can perform magnification. Like we can now build devices to see some objects as small as 1 micron(or even smaller than that). ...
2
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1answer
271 views

Misaligned lens in analytic ray transfer matrix to produce coma aberration

i want to do analytic ray tracing by using ABCD matrices and retrieve the wavefront at the detector via Zernike coefficients. $ \begin{pmatrix}x_{out} \\ \theta_{out} \end{pmatrix} = \begin{pmatrix}A ...
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2answers
235 views

Why does refraction make something look closer with an incident angle of zero? [closed]

The gaussian formula for a single spherical surface is defined as $$ \frac{n}{s} + \frac{n'}{s'} = \frac{n'-n}{R}$$ When the radius of curvature, $R$, is ...
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3answers
116 views

Physics of optics

Lights rays on the both upper and lower corner of the concave or convex lens show deflection. It is true . But I am trying to understand why light rays goes straight without bending while passing ...
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1answer
170 views

Why do convex lenses have a focal point? [closed]

Why do convex lenses have a focal point? How to prove mathematically that all the parallel rays that hit the lens meet at a single point? I can't see to have an easy solution to prove it.
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1answer
39 views

Beam Profile Through an Optical System

I am curious about how to counteract the effect different optical elements have on a beam profile. I know a good rule of thumb with lenses is that you should balance positive and negative ones to ...
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4answers
544 views

Phase delay in a thin lens?

Let the maximum thickness of a lens (on its axis) be $\Delta_0$, and let the thickness at coordinates $(x,y)$ be $\Delta(x,y)$. I have read that phase delay suffered by the wave at coordinates $(x,y)$...
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1answer
104 views

Why is the ray transfer matrix system products from right to left?

Example: link Process 1: T1 (Start) Process 2: S1 Process 3: T2 Process 4: S2 Process 5: T3 (End) System matrix = product of all process = T3.S2.T2.S1.T1 Why does it start from T3 to T1 and not ...
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1answer
41 views

Sampling with a lens

First off, I'm a beginner optics experimenter so bear with me... I'm looking to sample a light source. I am looking for a lens or prism that allows most of the light to pass through unaffected, while ...
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3answers
421 views

Do you get more photons from a magnifying glass?

Really elementary question- Do Magnifying Glasses produce more photons than what is put into them? If they don't, how do they make light appear brighter- Such as this scenerio: Small light through ...
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0answers
68 views

Lens equivalent depth of field

In digital photography, there's the principle of lens equivalency, according to which, when you shoot with a camera which has a smaller sensor than a full frame sensor (which is the same dimension as ...
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0answers
249 views

Determine the focal length of a biconvex lens [closed]

I'm struggling to find any information on this topic online. I've been asked to find the focal length of a biconvex lens with these specifications: Refractive index: 1.5 Total Height: 7.5cm Radius of ...
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1answer
519 views

“fish appear to be 30% smaller because of the curvature of the tunnel”

I recently visited an aquarium in Malaysia and there was a sign saying that the exhibits in their main tank appear to be smaller by 30% especially when viewed through their tunnel (https://www.youtube....
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2answers
418 views

Why would an infinity corrected objective lens produce an image without a tube lens?

I'm having a hard time wrapping my head around this situation I've come across. I'm essentially recreating a homemade microscope that my understanding would suggest shouldn't work. This setup uses a ...
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2answers
354 views

Is there a more accurate form of the mirror equation $\frac{1}{f}=\frac{1}{u} + \frac{1}{v}$?

In the mirror equation $$\frac{1}{f}=\frac{1}{u}+\frac{1}{v}$$ Q1: Are $u$ and $v$ the distances from the object to the mirror surface or the distance from the object along the principal axis to the ...
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1answer
108 views

Focal length of the thin lenses $ f = \frac {- f_1f_2}{\Delta}$, $\:$ $f' = \frac {f_1'f_2'}{\Delta}$

I am trying some exercises in optics and in my textbook (in the end of the book where are some unexplained formulae) i saw these: $$ f = \frac {- f_1f_2}{\Delta}, \quad f' = \frac {f_1'f_2'}{\Delta}...
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1answer
555 views

I have a plano convex lens and I want to increase the magnification

I have a plano convex lens and I want to increase the magnification but I cannot increase the focal length can I do this by increasing the curvature and dome height of the lens?
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0answers
46 views

transmission electron microscope beam divergence (limits on resolving power)

I have learnt about TEM recently and have a few questions. I've searched all across the internet but can't find the answer to whether or net electrons in the beam will repel each other thus diverge ...
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2answers
2k views

Why do convex lenses not disperse light like prisms, given that entry and exit points aren't parallel?

I understand that light entering a parallel block of glass at a non-90 degree angle will cause dispersion of colours within the block but that these will be refracted by the same degree upon exit so ...
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1answer
165 views

How do I experimentally find an image projected by a lens?

I know this is a simple question, however, I have never been taught the practical side to Physics properly so here we go. I know I can use the lens equation to find the image distance, but if I ...
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1answer
855 views

How do I find/calculate the radius of curvature of a convex lens? [closed]

I have a convex lens, and I want to calculate it´s radius of curvature. It´s focal length is 24cm. how do I do it?
2
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1answer
72 views

Why can't rainbows form at the start of a storm?

I was recently at a park looking at the gorgeous scenery. I looked above and saw thick grey clouds covering up 3/4 of the sky. The sun's light is still visible for 1/4 of the sky, and it looks low ...
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1answer
200 views

How does a compound lens reduce chromatic aberration?

A compound light microscope has two lenses: the objective lens (the lens closest to the specimen) and the eyepiece lens (the lens through which an image is viewed). My textbook states that chromatic ...
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1answer
232 views

Proof of Validity of Thick Lens Model by Hamiltonian Formalism or Otherwise

The paraxial imaging geometry of any axially symmetric optical system can be described by three real parameters: the axial positions of the two principal planes and one focal length (i.e. $f_f=f_b$ in ...
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1answer
172 views

When does a lens go from 'linear' to 'fisheye'

I recently ordered some lenses in an attempt to gather more light from an object being imaged in very low light conditions. I'm trying to use a converging lens with the object > 2f from the lens so it ...
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3answers
282 views

Why bi-convex lens give ignition?

Bi-convex is mostly used type of lenses.It can burn paper with help of sunlight.But why? Why bi-convex lens can give ignition when other lenses can't?
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1answer
2k views

Focal length of a pair of lenses

My textbook claims that for a pair of thin lenses separated by a distance $d$ the combined focal length of the system is: $$\frac{1}{f}= \frac{1}{f_1} + \frac{1}{f_2} - \frac{d}{f_1f_2}.$$ Can this ...
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1answer
3k views

Magnification - When is it negative?

In magnification, I keep on confusing the signs. From what I understand currently, magnification is positive when the image is erect. An image is only erect when it is a virtual image, therefore ...
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1answer
534 views

Calculate the diameter of of Gaussian beam at FWHM (or at 1/e2)

I need to collimate a gaussian laser beam out of a single mode fiber (NA0.15) with a single lens so that the full-width half maximum (FWHM) of collimated beam is 10mm. This question may sound naive, ...
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0answers
276 views

Using Standard Parabolic Mirror With Off Axis Source

I am trying to reflect as much light from a device as possible into a camera located 90* off angle from the light source. Currently I'm using a standard flat mirror placed 45* from the part and camera....
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1answer
70 views

Is it possible to construct a lens which focuses all the light rays from an extended object in one point?

A perfect lens focuses the light rays from an extended object (in a plane at a constant distance from the lens), in the focal plane corresponding to the distance of the object. Now there is an ...
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1answer
109 views

Spherical aberration entity vs. distance from the lens?

Consider a positive lens and spherical aberration, which causes the formation of that region of intersection of different rays as in picture. Named $q$ the distance of the image from the (idealized) ...
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1answer
206 views

Does a lens with a given numerical aperture (NA) increase etendue, even if it follows a source (e.g. fiber) with lower NA?

It is well known that the etendue of an optical system cannot be decreased - i.e. the brightness of a source cannot simply be increased by using lenses to try and focus something more tightly. ...
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1answer
201 views

Geometric optics multiple lenses

I am confused on how light rays behaved in this figure, specifically when it passed through the diverging lens. Why would the light rays converge when it passed through the diverging lens, when it ...
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2answers
60 views

Geometric optics- lenses

I was wondering why would light rays converge at a biconvex lens and diverge at a biconcave lens? Is it concerning on how light rays behave in a convex or a concave mirror? Also, is it possible to ...