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Questions tagged [lenses]

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When does the retina fail to recognize images of two closely separated points as distinct?

Our eye is a lens and lenses have a resolving power. The resolving power of a lens, physically speaking, is related to how good two closely separated points A and B can be distinguished as separate. ...
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How can I focus a laser in the gap between two slits?

I’m trying to focus a green laser in between two slits. The slit width is 0.2mm and gap between the slits is also 0.2mm. I measured the laser’s minimum spot size. It’s elliptical with major and minor ...
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Parabola black body heating

I'm having trouble figuring out why this following example of shenanigans wouldn't work. If you take a parabolic mirror (say from polished aluminium) with a magnification of M and construct it such ...
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1answer
25 views

What does the value of magnification gives [on hold]

I read a question in a book in which radius of curvature and distance of object was given and question was to find the size of image . In solution only magnification was given . So I am confused that ...
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2answers
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Does phase change occurs on refraction at a lens?

There is no phase change between refracted (transmitted) rays and incident rays, according to boundary conditions of electric field and magnetic field, in accordance with the Maxwell's equations and ...
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1answer
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What is a 3rd-order Fresnel lens?

The NPR News article and podcast Job Opening: Seeking Historian With Tolerance For Harsh Weather, The Occasional Bear talks about the Split Rock Lighthouse. That Wikipedia article links to the image ...
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1answer
19 views

Virtual and Real Images

I am well thorough with the concept of virtual and real images for a single lens/mirror. However I don’t understand how it exactly works for complex system of lens .eg-two or three lens with a ...
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1answer
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Determining lens and sensor distance for narrow focus

I have the following items: a round target object, approx. 6mm in diameter a lens, focal length 20mm, F/2.8 a camera sensor, optical size 1/4" (note: I know this camera has a fixed-at-infinity lens, ...
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1answer
27 views

Determine variable radii of a lens [closed]

How can I determine the radii of a thick lens if I only know their proportion? I can find a lot of examples determining the focal length from the radius but barely anything about the other way around. ...
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1answer
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Holographic “lens” - controlling light diffraction angles with silver halide film

I'm trying to develop a way to control the "exit angle" (diffraction angle) of a monochromatic light source. For example: taking a laser; spreading the beam; and directing the light at a piece of ...
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1answer
47 views

Focal length for thick lens [closed]

How can I find the focal length of a thick lens by the method of ray tracing ? I know the ray matrix method but by ray tracing I don't get to an answer.
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2answers
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Why do we see things upside-down when we’re upside-down but not a camera?

If I do a handstand, everything looks upside down (which is originally what we see if we’re upright but the brain switches this). I assume this is because the change in how light rays enter our eye. ...
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Hard Lens Question

In the explanation to this question, it states "the 140cm focal point is where the image needs to be located". Can someone explains what this means? A certain farsighted person cannot focus on ...
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Interference using composite lens

I encountered a question while attempting an exam. I cannot really understand how to go about it. It is clear that the concave part forms the image at a distance $3 \lambda /2$ behind the lens, and ...
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2answers
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Polarised glasses for high astigmatism and myopia [closed]

So I have -4 for both of them, which results in -8 in total (same for left and right eye). At my optician, I have to choose the best package they have to make sure my sunglasses can be as light as ...
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1answer
13 views

Does the order of analysis matter when considering multiple lenses and mirrors?

Say we have an object $O$ that is to the left of two lenses. Let's say that the first lens $L_1$ is to the left of $L_2$, the second lens. Assuming we know the type of each lens (concave or convex), ...
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Optics that translates object to image by a constant amount

For some application I was interested in an optics s.t. for any incoming ray the outcoming ray is parallel to the incoming ray and shifted by a distance $d$ (independent of the incoming ray) along the ...
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1answer
28 views

How to know if a thick lense system is divergent or convergent

I know that the sign of the effective focal lenght (f) of a lense will determine if a that lense is divergent(f<0) or convergent(f>0), but with a system made of a combination of thick lenses and ...
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The ideal shape of a plano-convex lens

What's the type of the ideal shape of a surface of a plano-convex lens to focus a parallel beam at the point? Considering the lens turned its flat side to a beam. Surely it must be aspheric: ...
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2answers
80 views

Prove that a converging lens has 2 object distances for which there exists an image

I've been struggling with this for a while now. I feel that proving this is actually way easier than what I think it is. I'm just going to copy paste the question here: A light bulb (the object) is ...
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1answer
113 views

Seeing virtual image in convex lens of object kept beyond focal point

Beyond the focal point, $f$, a convex lens only forms real image. However, I see an inverted virtual image of a distant object when looking at the lens from a distance. If the image of the distant ...
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3answers
51 views

Why do we see an object with more clarity if more light rays from it enter our eye?

When I ask people what is the difference between more light rays diverging from a point and entering our eye and less rays diverging from a point and entering our eye.They say that more the light rays,...
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3answers
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Virtual images - Work of a brain or work of a lens?

I am just a high school student trying to self study, so please excuse me if this question sounds silly to you. Many people tell me that virtual images are formed when two rays that are diverging ...
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174 views

Can we see a point with only one ray or do we need two rays?

I am just a high school student trying to self study, so please excuse me if you find the question silly. My teacher says that we can see a point when a ray of light from the point is reflected into ...
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1answer
44 views

Which of these 2 methods for calculating the focal length of a concave mirror is more accurate?

I have done an experiment to measure $f$ the focal length of a concave mirror. I have a list of 8 values for $u$ the object distance and 8 values for $v$ the corresponding image distance. I ...
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1answer
27 views

Is the spatial coherence of light a requirement for creating a well-collimated light beam?

I was wondering if, for creating a well collimated light beam, the spatial coherence play a role. In particular, I understand that a laser beam can be well-collimated with respect to light coming from ...
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4answers
42 views

determining focal length of converging lens

the focal length is the distance between the center of the convex lens and the focal point. in the image illustrated above, we obtain focused image at the (position of image, inverted yellow arrow) ...
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1answer
84 views

How is the image distance negative?

Following is a problem from book: "The near point of a person's eye is 53.0 cm. To see objects clearly at a distance of 24.0 cm, what should be the focal length of the appropriate corrective lens?" ...
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3answers
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Could a converging beam of light be converted into a parallel one?

A parallel beam of light comes out of a plano-convex lens and start to converge into focus, the question is, at that focal point, could the beam be parallelized again so it maintains the focal point ...
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2answers
31 views

Numerical Aperture of thick lens

How to calculate numerical aperture of a thick lens ? Suppose we have a thick biconvex lens whose radius of curvature 24.5 mm, center thickness 9mm , diameter 25.4 mm and focal length 25.4 mm. Then ...
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1answer
61 views

Sign convention in combination of lenses

The problem statement: Two convex lenses, each of focal length 10cm, are placed at a separation of 15cm with their principal axes coinciding. Show that a light beam coming parallel to the principal ...
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2answers
34 views

Thick vs thin lens

What is the criteria to know whether a lens is thin or thick ? Suppose we have a lens of r1= 10 mm , r2= -10 mm and thickness is 5 mm. So, with this information what can we say about the lens whether ...
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1answer
31 views

Is focal length of Plano Concave lens $f=\cfrac{R}{\mu - 1}$ or $f=\cfrac{R}{1 - \mu}$

Let the radius of curvature of the concave part of the lens be R. Then when using the lens makers Equation, $$ \cfrac{1}{f} = \left(\cfrac{\mu_2}{\mu_1} - 1\right)\left(\cfrac{1}{R_1} - \cfrac{1}{...
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Spherical aberration plano-convex lens

What is the formula for plano-convex lens spherical aberration for an object at an infinite distance (incidence rays are parallel to the lens axis) and facing the spherical surface?
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What is the optical Lagrange invariant of an afocal system?

I am solving an optics exercise that requires to design a Keplerian telescope with a given magnification M (negative), a certain object size L and the restriction of not having lenses faster than F/1 (...
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1answer
23 views

Using a collimating lens for beam interference

If I have two beams of light which are incident on the same point of a collimating lens, will they emerge as a single beam and interfere? I've attached a drawing below: If not, what happens?
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How do I calculate the integral for the point spread function of an optical system without the fresnel approximation?

For an object located at the $(x_o, y_o)$ plane, and a lens located at the $(x, y)$ plane, the image is produced at the $(x_i, y_i)$ plane. We can consider the image field $U_i$ to be the sum of the ...
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2answers
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Proof that light rays take the same time to reach the focal point of a lens

In a thin plano-convex lens, if the wave front is perpendicular to the lens axis, all of the rays are in phase and are focused at the focal point. Can we use the lens geometry to mathematically prove ...
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1answer
69 views

Distance between the luope and the virtual picture: I can not see any

I have a biconvex lens. f=45mm. (This is a loupe). I have an object (G). This object is G=64mm broad. When I place this object in a distance of g=42mm in front of the lens I get a virtual picture. I ...
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What is the theory behind imaging a precision pinhole?

In my efforts to characterise a 0.67 NA microscope objective (working distance of about 15mm, effective focal length of 25mm), I have placed a 20 micron precision pinhole at the focal plane of the ...
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2answers
33 views

On-watch lens to correct for presbyopia?

I'm wondering if it is theoretically possible to construct a lens that overlays directly on top of a watch (or phone) that warps the image in the same way that reading glasses (much farther away) ...
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1answer
72 views

Ray-tracing on a thick lens [closed]

I'm having some troubles drawing down the main rays on a thick lens. In particular I don't understand if the parrallel ray which comes from the right will start to divert intercepting the MP1 or the ...
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1answer
32 views

Maximum possible magnification with glass lenses

What kind of magnification function does stacking lenses produce? Is the magnification factor a multiplicative, additive or a different function? For example, does stacking two concave lenses with ...
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1answer
27 views

Optical convolution processor

I was reading this paper: But I'm not agree with its conclusion (I think it is wrong). Indeed, we have (I use a slightly different notation, hope it's clear): $$U(x,y,2f)=kost \ F[g(x_{1};y_{1})]_{(\...
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Collimated beam focused with 2 lenses, both plano convex or one plano convex and one biconvex?

I have a collimated laser beam. I focus it with a plano convex lens with a focal length of 1000mm. Then 83 mm further away from the first lens, a lens is placed with focal length 750 mm. So when the ...
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Which focal length is needed to determine minimum focused spot size in 2 lens system?

If you calculate the minimum spot size of a beam, it depends on the focal length to to power 2. But if you have a lens system with 2 lenses, does the focal length in this case represents the effective ...
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Can you polarise a lens by rubbing it with your finger?

Here's a phenomenon that you all might have come across . I took two photos on my phone, keeping it in landscape mode. I noticed that the light rays get polarised, or rather "smudged" when I rubbed ...
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If you have 2 lenses, is it better to place the stronger lens first or the other way around?

I need to focus a laser at a certain distance. But everytime I perform the experiment, the distance between the laser and the surface will be slightly different. Therefore I will fix the lens with the ...
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Concave Lens Magnficiation

Is there some formula to calculate how large an image of a light source will appear on a screen based on the lenses distance from the image and the lenses distsance from the screen? For example, if ...
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3answers
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Why do lens (convex) not introduce any path difference to light incident on it?

My understanding is that the top rays spend less time inside the lens where the speed of light is slow and the middle rays spend more time inside the lens so the time is kind of compensated . But I'm ...