# Questions tagged [geometric-optics]

The subfield of optics in which light propagation is approximated in terms of rays. It mainly includes reflection and refraction on surfaces.

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### What is the proof that we can use virtual object to know the place of formation of image in case of convex/concave lens?

What is the proof that we can use the location of virtual image in the lens formula to get the location of the image (convex/concave lens)? The following problem might make my question more clear. The ...
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### Given that light spreads out as it travels, why do distant objects appear smaller than nearer objects?

I realize this might be a silly question but it is plainly true that, for example, a lighthouse beacon or any powerful light source, produces a much larger "spot" the farther it falls from ...
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### Focal Length as it relates to Field of View

I understand that in physics, for a converging lens, the focal length is based on the refractive index of the lens material and its curvature. However, I started reading a bunch of photography ...
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### Field of view calculation

On the schematic bellow for a transmission imaging is the Horizontal field of view given by? f=h*WD/horizontal FOV Everything in mm. Is the working distance the distance of L7 to the sample (thus ...
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### Normal lying inside the mirror surface

In the problem above what does the question means by given normal lying inside the mirror surface? Is it has something to do that they have i and j components same. I also wanted to know what does the ...
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### How does an object's shadow pattern depend on size of light source?

A friend of mine unintentionally did an optics experiment. Basically, she wanted to cover her bedside lamp with a pattern of small holes, although she wanted the light projected from the bedside lamp ...
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### Prism, Dispersion and Deviation

A very straightforward question- Is it possible to have no dispersion and no deviation for a combination of prisms? And by prisms, I mean, a triangular one, not a glass slab. If so, please provide the ...
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### Ghosting/Unwanted refection with cube beam splitter

I am new in working with an optical setup. I have a small setup to mimic a 3D printer motion stage. So, it consists of a laser hitting on a cube beam splitter. The transmitted one is dumped while the ...
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### Why does a converging lens create an upside down virtual image with an object further than the focal point?

The thin lens equation shows that when there is an object further than the focal point, there is a real image formed on the other side of the lens, and this principle is used for cameras, eyes, etc. ...
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### Proving parallel rays converge to focus using Fermat's principle for a concave mirror

Fermat's principle is a boundary value problem which gives possible paths as it's answer. And I understand how it's applied to give possible paths between two arbitrary points. And following from the ...
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### Imaging using refraction and its application on prisms

I stumbled upon a problem when trying to explain how a spectrometer with a prism works based on geometrical optics. I started from the basic example of image formation based on refraction as it is ...
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### Why the optic axis of an crystal should has a proper direction; why it cannot be a single line? [closed]

In many books it is written that the optic axis of a crystal is a direction rather than a single line! I really cannot understand what is the necessity of the direction and why I cannot say that it ...
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### Understanding details of the chromatic aberration depicted in this simulated image from NASA

Phys.org's The detection of phosphine in Venus' clouds is a big deal, and here's how we can find out if it really is life contains part of a NASA/JPL-Caltech image which is on the cover of Aerial ...
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### Laser spot size with pinhole

I am currently trying to find the focus of an IR laser beam by using a 300 $\mu$m pinhole. Now, when I am scanning the pinhole across the beam and plotting the pinhole position vs the laser spectrum ...
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### Collimation issue with an DIY echelle spectrograph

I am trying to make an educational echelle spectrograph using easily available materials, basically in a cardboard box. An echelle grating (36 lines/mm) needs another prism to do a cross dispersion ...
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### Why do plano-convex lenses reduce spherical aberation?

I keep reading this in comparisons of different kinds of lenses but I don't understand why the flat side would change the amount of spherical aberration if the focal length still has to be the same?
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### Extraordinary wave [closed]

In anisotropic media, for extraordinary wave, I don't understand how can the power flow not be in the same direction as the propagation. I can't find a physical intuition for it.
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### Can the mirror formula be applied if object is not placed on the principal axis of the mirror?

I have seen the derivation of this formula, and it was derived under the case that the object was placed on the principal axis of the mirror. If somebody knows, can they please share the formula to ...
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### Do we assume normal incidence for wedge fringes?

In wedge fringes we have fringes of equal thickness. Does this mean we only see equal thickness fringes when viewing very close to normal incidence, what are the fringes like for larger angles then?
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### How are wedge fringes like Young's slits fringes?

It says in my optics lecture notes that by drawing virtual image point sources one can see that wedge fringes act like Young's double slit fringes. However, if this is the case, why do we observe ...
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### Is it possible to optimally transmit solar radiation by a system of multiple optical fibers?

As we all know, if an optical fiber is designed with the right material and properly bent, light can be transmitted along the fiber with very little attenuation. Figure 1 shows the interaction of ...
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### Is Babinet's Principle only valid in the Fraunhofer condition?

I have seen that it is often stated that Babinet's principle is only valid in the far field limit/Fraunhofer condition as it makes use of the linearity of the fourier transform. However couldn't you ...
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### Lens Maker equation and Geometrical equation

or a myopic swimmer with a prescription of -7.0 diopters, what should the radii of curvature of the lens surfaces be if the goggles are made from a high index plastic of n = 1.6? First, what is the ...
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### What is the geometric derivation of 2D Fraunhofer aperture diffraction?

In this derivation, I can understand the formulas stated for 1D diffraction for both x andy (with the phase difference $\delta= ksin\theta y$) in the far-field limit, but how can we just sum the ...
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### What does equipartition of modes mean in ray optics?

Consider light as rays interacting with refractive boundaries - no polarization or diffraction, but with scattering - a fixed probability of a ray changing angle per unit time. First of all, what ...
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### Which path does light take through a lens?

In the picture below, the three principal light rays are drawn refracting through the lens , forming an image on the other side. But which path does the light actually take? That is , if i place my ...
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### Doubt regarding mirrors

This question of mine is regarding some general observation. From ray diagrams it can easily be concluded that using a real object, we cannot get a real image from a plane mirror. But, if we shine a ...
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### Minimum length of full-length mirror - can anyone explain? [closed]

this example by the answer but I don't understand the steps. So please if you understand or have another steps drop it . Thanks
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### What does it mean that light “will not reach your eye unless your eye is positioned at just the right place” in specular reflection? [closed]

I am confused about the following passage from my textbook: When light is incident upon a rough surface, even microscopically rough such as this page, it is reflected in many directions, as shown in ...
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### Will the medium boundary act like a spherical mirror?

I was studying geometrical optics the other day and my teacher told me about the concept of critical angle and total internal reflection. He had taken an example in which a beaker was filled with a ...
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### Virtual image of a virtual object

During early classes we are taught that real image of a real object is inverted with respect to the object. Similarly virtual image of a real object is erect with respect to object. My doubt is that ...
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In the book 'OPTICS' by Eugene Hetch it is written that, "the optic axis is actually a direction and not merely a single line". I can't understand why it is a direction, not a single line?
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### Focal length of lens combination [closed]

The adjacent figure shows a thin plano-convex lens of refractive index $μ_1$ and a thin plano-concave lens of refractive index $μ_2$, both having same radius of curvature $R$ of their curved surfaces. ...
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### How does light get energy when moving from one medium to another?

It is said that the speed of light increases when moving from optically denser medium to rarer medium but as light can be considered as a particle how does it get the energy to increase it velocity
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### Derivation for optical path length and the origins of the formula

So I've learnt that the formula for optical path length is $OPL = ns$, where $n$ is refractive index of the medium and $s$ is its geometrical length, the problem is i cant really get around this ...
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### What are Gaussian Spherical Waves?

What are Gaussian spherical waves? and Is it necessary for a Gaussian spherical wave to be a laser beam? I found the term in the paper Opt. Eng. 54, 035105 (2015) (eprint).
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### How does Fermat's principle make light choose a straight path over a short path?

This is a thought experiment where I have made a "C" shaped hole inside diamond. The refractive index $(\mu)$ of diamond is 2.45. Say we shine a laser from top of the "C" as shown. ...
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### Problem involving lenses and mirrors [closed]

A biconvex lens of focal length 15 cm is in front of a plane mirror. The distance between the lens and the mirror is 10 cm. A small object is kept at a distance of 30 cm from the lens. The final image ...
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### Resolving power of telescope and circular aperture

From the formula of circular aperture we get: sinθ=1.22λ/D But according to this formula, the θ is the angle on the side of the Airy disc formed. The formula for angle of resolution for a human eye ...
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### Optics: mirrors

While drawing ray diagrams for plane and spherical mirrors, what is generally taken as the point of observation? Eg, If a concave mirror is presented with, say a wire turned into a triangle, placed ...
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### What is the combined lens formula for Effective Focal Length (EFL) when $d > f1+f2, f1,f2>0$?

I know the standard combined lens formula as: $\frac{1}{f}=\frac{1}{f1}+\frac{1}{f2}-\frac{d}{f1\cdot f2}$ But i observed that the formula is not working when d is greater than f1+f2. (also both f1 ...
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### Confinement factor for an optical fiber

I was reading the chapter about optical fibers of "Fiber - optic communication systems" and I have read this statement: The fraction of the power contained in the core is given by the ...
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### Light rays || to each other but not Principal axis

If a Ray of light travelling parallel to principal axis is incident on a concave mirror, then after reflection it will pass through focus. If however we have two rays of light that are parallel to ...