# 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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### 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 ...
407 views

### Why does the sun not burn your retinas when in peripheral vision?

After going to the ophthalmologist and having bright lights shone in my eyes, I was thinking about how the brightness only hurts when I looked at the light. When it was in my peripheral vision, it ...
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### 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 $$\frac{1}{f_{eq}}=\frac{1}{f_1}+\frac{1}{f_2}-\frac{d}{f_1f_2},$$ but the ...
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### Out-of-focus color in reflective microscopy with Köhler EPI-illumination

It is well known that Köhler illuminator in optical microscopy is designed in a way to ensure uniform illumination of the field, often with adjustable apertures to allow as little light as possible to ...
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### Changing the apparent focal distance of an object

I'm not completely confident this is the write SE site to post this on, but it seems like the most relevant one. I want to make an object (with negligible thickness) that is around one to five ...
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### How does the quality of the reflected light compare to the emitted light? And how do I manage this (reflected) light quality well?

I am designing an interferometer for an experiment. The setup consists of (1) the laser source, (2) the interferometer itself (consisting of optical components and photodetector(s)), and (3) the ...
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### What is aperture of a lens?

I read that aperture of a lens is the surface from which refraction takes place and it is represented by the diameter of the lens. So, by saying that the aperture refers to the surface from which ...
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### Spot size for objective (not infinity corrected)

A fundamental axiom of imaging in optics is the resolving power of the lens system, which is directly related to the smallest possible spot a lens can form. For an ideal lens with a numerical aperture ...
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### 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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### 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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### 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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### 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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### 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 ...
117 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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### 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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### 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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1 vote
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### Parallax free projected image on diuelectric coated glass

I'm not a physician at all, just a computer scientist, so be nice with my average brain. I'm working on an Optical System composed of: A IR camera A pico projector (TI DLP2000) and a clear glass Anti-...
1 vote
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### 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 ...
1 vote
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### Is the lens image, a combination of diffraction patterns?

As I was reading through Luigi Picasso's Lectures in QM, I came across this paragraph where he explains the reason behind the resolution power of the optical instruments. He writes: Let us now ...
1 vote
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### Do convex lenses start to act like concave lenses at twice their focal length?

I'm trying to create a cheap concave lens effect for a class I'm doing. It seems like a convex lens starts to create a similar effect anywhere passed twice it's focal length. It also makes ...
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### Fringe pattern and ripples in the fringe visibility plot from interferograms

I am using a lens testing interferometer, where I record 4 to 5 interferograms with a 90$^{\circ}$ phase step between consecutive interferograms. In addition to the interferometer, I have also created ...
1 vote
205 views

### Changing focal length of diode-based laser

I have a blue laser diode that has a focal length of about 2cm. I would like to extend that, so I can engrave things further from the laser, and to lenghten the distance where the beam is focused ...
1 vote
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### What causes the distortion of an image when seen through a water droplet?

I'm trying to explain what causes an image to be distorted when seen through a water droplet. Specifically, my example is that of a drop of water on a car window. We can see that the image is reversed,...
1 vote
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### 4f Imaging System with cylindrical lenses

I have seen an imaging system (4f) which uses two cylindrical lenses in a 4f configuration, but with an extra cylindrical lens at the fourier plane. How does this work? Edit: Posting an image of the ...
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### Hyperbolic lens shape and aspheric surfaces

In Optics, Hecht, the author states that the perfect surface for a lens shape will be a hyperbola. He essentially derives this answer by writing the optical path length from F1 to A, then A to D, and ...
1 vote
58 views

### Does oversize lens for focusing small laser beam width affect the focal length of lens?

I am working with optical setup where I am focusing collimated light with 2" size lens. Beam width of collimated light is around 20 mm 1/e2 diameter. The focal length of focusing lens is 750mm. I ...
1 vote
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### Small Angle Approximation in Lensing Equation

In reading an article about gravitational lensing, I was pretty confused by the fact that the extra path travelled through the Lense compared with the direct path $OS$, in small angle approximation is ...
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### Why conics is the "perfect" shape of lenses?

It is stated on this wikipedia page that we have the following formula $$z = \frac{r^2}{R\left(1+ \sqrt{1-(1+\kappa)r^2/R^2}\right)} + \text{ (higher order terms)}$$ for the usual shape of an ...
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### What kind of lense do you need to use to get a picture of the sun that looks like this?

This is a picture of the sun from the moon. When I look at the sun with my eyes, I see something like this: But the above picture is perfectly round, which makes me think it has to do with the shape ...
1 vote
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### Objective lens and Eyepiece of a compound microscope

Why is the objective lens always powerful than Eyepiece of a compound microscope? Will it not work if Eyepiece is more powerful? In a book it is given that Eyepiece has larger focal length.
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### How do electromagnetic lenses magnify the image?

In optical microscope both objective and eyepiece are used to magnify the sample image. Magnification is determined by laws of geometrical optics (intersection of optical beams from the same point of ...
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### Why objects dont appear closer and smaller to a myopic person and far and larger to hypermetropic person after wearing spects?

I am a myopic person, and wear a concave lens. It is taught to us that lens I wear help to form image on my far point and thus help me to see far object. 1.But we have also learn that concave lens ...
1 vote
411 views

### What materials can bend or reflect gamma rays?

I have heard that gold can be used as a lens for gamma rays, but what exactly could reflect them? Having this technology could make something like a Dyson sphere much more efficient, I believe.
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### Determine lens system for known magnification and available space

I'm trying to create a system of two lenses with a set magnification in a limited space for the setup, i.e. the distance from the object to the first lens $g_1$ has a minimum ($152\,$cm) and the whole ...
1 vote