Questions tagged [lenses]

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What is Curvature of eye lens?

I wanted to know what do we mean by "curvature of eye lens", is it the reciprocal of $r$ i.e $c=1/r$ or is it synonymous to radius of curvature of the eye lens. Moreover how does aperture relate to ...
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564 views

General proof of formulas of geometric optics?

In most lf textbooks formulas of geometric optics like lens maker formula and base formula for that are proven (or rather verified from my point of view) by taking specific case (ray diagram) and ...
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238 views

What criterion did Abbe use?

For a microscope (correct me if I am wrong) the Rayleigh Criterion gives us: $$ R=\frac{1.22 \lambda}{NA_{condenser}+NA_{objective}}$$ But with the Abbe diffraction limit: $$ R=\frac{\lambda}{NA_{...
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191 views

What does it mean for a Fresnel lens to have two finite conjugates?

I'm in a situation where I need to reverse engineer a product that my company already manufactures and sells, but it wasdesigned too long ago for anyone to remember. It uses a Fresnel lens with the ...
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63 views

Colour of artifacts in a lens flare

I'm adding a lens flare to an illustration; which got me thinking: Are the colours of the artifacts (hexagonal/circular) which appear in a lens flares purely random, or much like a rainbow (...
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3answers
98 views

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
54 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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2answers
44 views

Light hitting a GRIN (Gradient-index) lens at the optical angle

In the image below, rays of light are hitting the GRIN (Gradient-index) lens at the optical angle and then converge towards the optical axis. Why do they do this? The refractive index is only a ...
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495 views

Why do my glasses make the ground look tilted?

I just started wearing glasses to correct my myopia today. I have -0.25 spherical and cylindrical power in my right eye and -0.5 spherical and -0.25 cylindrical in the left eye. Everytime I look at ...
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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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259 views

Why google cardboard uses double-convex aspherical lenses?

Google cardboard VR version 2 uses double-convex aspherical lenses with different radius of curvature. The full specifications are in the official google cardboard site in the manufacturers section, ...
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1answer
69 views

How does a weak lense perturb the Minkowski metric?

From 'Introduction to Gravitational Lensing' by Massimo Meneghetti: The metric of unperturbed space-time is the Minkowski metric, $$\eta_{\mu\nu}=\begin{array}{lcr} \mbox{} & 1 & 0 & 0 &...
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63 views

Increase the collection effciency of lens array

In an experiment I am trying to image a phosphor surface on a camera using a 3x zoom lens. The distance of phosphor surface to lens input surface is ~100 mm. The effective focal length of the zoom ...
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662 views

How was microscope-level zoom created by a lens and a water droplet?

It was a rainy night. My glasses were speckled with fresh water droplets. I looked at a distant street light and I was surprised to see cells - a single cell was zoomed in to the level where I could ...
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52 views

Optical bandpass filter at focal point of lens

Optical bandpass filters are designed for a particular angle of incidence (AOI), e.g. see Fig 4 here. However that is for the ray picture of light. Imagine I have a thin bandpass filter positioned ...
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213 views

The sign of a focal length

We know that for converging lens, $f>0$ , for diverging lens, $f<0$. But for many materials I have read so far, it says that: "the focal length of a concave lens is 8 cm." I thought that the ...
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94 views

Given a focal length and an aperture of the telescope, what is its field of view?

While I know FOV of scope is equal to FOV of eyepiece divided by magnification. How can one find FOV given only the focal length and aperture of the telescope?
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617 views

Interpreting Seidel Aberration coefficients

I am trying to model a simple system in Zemax (though I think the question is general and is not limited to Zemax app), but the ray-tracing does not seem to be consistent with the analysis of the ...
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1answer
868 views

How to calculate beam spread of a non-point light source via an aspheric lens

I need to determine the angle, or rate of divergence of light from a single aspheric lens when I place a non-point light source (e.g. LED array) at a given distance from the lens which is less than ...
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42 views

Infinity Corrected Microscope vs. $4f$ imaging system

This questions concerns three types of microscope systems and the differences between them. Let me lay out my understanding of these three types of systems. I am imagining imaging with a camera so ...
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1answer
20 views

What is the difference between longitudinal chromatic aberration and spherochromatism?

In lens design textbooks, a distinction is often made between longitudinal chromatic aberration and spherochromatism. (See for instance Kingslake's lens design book.) What is simple way to understand ...
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17 views

Polishing Spherical Refracting surface vs Lens

My text book states that When we polish a spherical refracting surface (sphere) it doesn't behave as spherical surface and mirror .It still behaves as spherical surface. The polished side is just ...
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24 views

How far will the imaging be? And is it possible to make it farther?

So currently I'm trying to make a smart glasses, where you have a projector that projects an image onto transparent flat glass, and some of the light will reflect into your eyes (something like the ...
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18 views

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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1answer
38 views

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
38 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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1answer
57 views

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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3answers
174 views

Identifying real and virtual images (convex lens experiment)

I m really confused between virtual and real images. While doing a convex lens experiment using optical bench (I have attached an image), when I look through the lens I see an inverted image. As this ...
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1answer
19 views

What kind of lens would eliminate distortion through a cylinder wall?

Suppose you are trying to look at an object inside of an acrylic cylinder. What kind of lens could you use on the outside to eliminate the distortion caused by the wall? The image can be inverted.
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81 views

What are laser achromats?

I came across "we used Nd:YAG laser achromats" in a paper, and I was wondering what exactly is the purpose of achromats here. The paper in question is "Dynamics of laser-induced cavitation bubbles ...
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39 views

working to understand virtual images

I'm starting to understand how to use lenses a bit more, but I'm still pretty lost. I'm building a project that's extremely similar to this one with the implementation. I think my biggest challenge ...
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2answers
70 views

Does anti-blue coating work less effective on high power lens?

I purchased a spectacle from an online website with anti-blue coating. The features of this product is mention here. Once I receive it, I started using the product without testing the anti-blue ...
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2answers
69 views

Imaging resolution with laser

The transverse optical resolution of a lens, as determined by its point spread function, can be approximated as $w$ ~ λ/(2$NA$), where $NA$ is the numerical aperture and λ is the wavelength of the ...
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50 views

Effects of lenses

I have three convex lenses that I'm arranging so as to function as a crude magnification device. My question is about the image that I see. It seems that no matter how I arrange them, with respect to ...
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1answer
179 views

How do we prove that parallel light rays (which are not parallel of principal axis) meet at focal plane?

Parallel rays coming from infinity are said to meet at focal plane.I was looking for the proof of that phenomena
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53 views

Will a combination lens have symmetric focal length on either side?

In this discussion on finding the focal length for combination lens, the image described in the answer shows the measure of focal lengths. Description of the Gullstrand equation also talk about front ...
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64 views

Biconvex lenses in 2 media

The question is what is the formula of the focal length of a biconvex thin lens if object medium is water and the image medium is air. I know that we have: 1/f = (n-1)*(1/R1 - 1/R2) , if the medium ...
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31 views

Screen distort for corrective lens

Can we apply a screen distort for corrective lens for eye ware instead of using a lens maker? Just test at home with a phone screen and buy at shop. To reframe the question can we bring to effect a ...
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1answer
70 views

Can we see through the central obstruction of a lens?

I have a very basic question in optics inspired by this article from the University of Stanford which clearly states that one should see a light source through a mask in the middle of a lens if the ...
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29 views

In this situation, is an endless sequence of images (theoretically) formed?

I was dealing with an optics problem, where an object is placed at $u= -60$ cm in front of a biconvex lens of radius of curvature $R=30$ cm and refractive index $\mu=1.5$ . Simple calculations show ...
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2answers
379 views

Light focusing on long distances

If I have a green laser (500 nm wavelength) with initial beam diameter 3 mm, with proper lenses I can easily focus it to 1 mm or 0.5 mm for small distances like 10 cm. My question is can I focus it ...
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1answer
53 views

How are progressive lenses made to allow for continuous changes in prescription?

I recently got progressive lenses in my glasses and have been wondering how they achieve the (at least seemingly) continuous change in prescription? Is the glass formed to have a continually changing ...
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1answer
1k views

Lensmaker's equation for thick lens in two different media

I've been looking around and I've found the lensmaker's equation for thick lens to be $$\frac{1}{f} = \frac{n_{lens} - n_{m}}{n_m} \big( \frac{1}{R_1} - \frac{1}{R_2} + \frac{n_{lens} - n_m}{n_m} \...
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187 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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0answers
157 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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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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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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275 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
69 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
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. ...