# Tagged Questions

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### Can focal point of a lens be a line instead of a point

Is there any lens OR can we have a lens that will focus light in form of a line instead of a point. Some sort of a rectangular convex lens.
644 views

### How to use a magnifying glass or any lens to enhance small light power?

I am currently trying to amplify a tiny amount of light so that a photodiode will recognize it. In order to amplify the light I thought about using a magnifying glass since I got to know that such ...
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### How did physicists determine how to orient the wave guides for this optical meta lens?

What kind of physics and mathematical tools are used to develop this technology? As described in the link, Researchers have demonstrated the first planar lens that works with high efficiency ...
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### Spherical aberration: circle of least confusion and diffraction limited spot size

I need an estimate of the relative sizes of the circle of least confusion (spherical aberration) and the diffraction limited spot size for typical real lenses. I've seen plenty of discussions, but ...
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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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### What is a good book to self-teach optics?

I'm interested in camera lenses and how things like barrel distortion and lens flare happens, but know that one cannot just start there. I'm a math major and I've worked out of Strauss PDE book so I ...
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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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### Coordinate Equation of a curve which bends all the parallel incoming rays from infinity towards a single point

How should i proceed on to find the coordinate equation of a curve such that it bends all the parallel rays coming from infinity towards a single point. Yes I know that it would be a 2nd degree ...
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### Relationship between angular magnification and how much bigger the image appears

How is the angular magnification of a magnifying glass related with how much bigger the image appears to the user? Is it simply the same? If yes, why? (Let's assume that the object is placed in the ...
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### Lens and Mirror Grinding

I am actually grinding my own lenses ( I am trying). Now I have been continuously using the chordal stroke for atleast 3 hours but i am unable to see any depreasion be it convex or conacve on the tool ...
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### If I placed a converging lens in water, would its surface power change?

If I placed a converging lens in water, would its surface power change ? The first case when the lens is in air then placed in water; does the surface power change or remain the same?
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### Sun light collimation

Is it possible to make sun light collimated in such a way, to increase energy density and keep it more less parallel? like on the Earth we have intensity of sun approximately 1300 watt/m2. If we use ...
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### Calculating f-stop with given focal length and desired depth of field?

I have a varifocal zoom lens set to a desired focal length and at known distance from the subject. I also have a desired depth of field. Given this information, can I calculate a theoretical f-number ...
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### addition of two lenses with a finite separation in between

Suppose there are two lenses with focal length $f_1$ and $f_2$ respectively. The effective focal length $f$ when they are combined is $1/f=1/f_1+1/f_2$, but this formula assumes the separation between ...
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### What are the right signs? [closed]

This is a question provided in my book: An object of height $2\ \mathrm{cm}$ is placed at a distance of $2.5f$ from a concave mirror where $f$ is the focal length. Find the height of the image. ...
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### Breakdown of Snell [closed]

I have reason to believe the following: If we are using an accurately formed thin prism, with an apical angle of let's say 2 degrees, and direct a monochromatic source beam thru a slit onto the ...
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### Focal length value for infrared camera

I always thought that the 5 mega pixel camera attached to my Android tablet wasn't worthy of seeing the infrared. But I was wrong! The infrared led protruding from my circuit happily shows up it's ...
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### Calculating the diameter of Jupiter through an image

I took an image of Jupiter through my 8" Dobsonian Telescope, attaching a DSLR and a 1.25" Barlow Lens where the eyepiece goes, as shown in this video: https://www.youtube.com/watch?v=reFxoF3XoaU ...
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### Why can't incoherent light be collimated as well as laser light (e.g. in a laser pointer)?

Why does a laser pointer contain a laser diode, and not just an LED? A laser pointer contains a laser diode, which essentially shines coherent light over a large angle, and a collimating lens, to ...
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### How come lenses alter the path of photons?

From what I know, photons are theorized particles and believed to be massless (just energy) and travel at the speed of light. How come a lens, which is an object made of atoms, can bend a light path? ...
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### Does curving only the inner surface of a diving mask prevent blurred images?

Diving masks often have lenses built into the glass for divers who do not have perfect vision. The lenses in a diving mask faceplate often only have a curved surfaces on the inside glass. Why is this ...
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### What is the relative importance of lens element quality in a multiple lens system? [closed]

I tried grinding a custom lens out of acrylic glass (diameter 20mm, focal length 30mm). Not very surprisingly, the result is a quite poor quality lens. I think it mostly suffers from geometry and ...
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### Optics to correct focal distance across a plane

I have a laser beam which is focused to a point at a certain distance. I'm then going to use a galvanometer to scan that beam across a plane. Obviously, as the beam scans across the plane, the ...
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### Tricky Optics Questions, shifting lenses [closed]

A candle is placed at a fixed distance in front of a wall. A lens is inserted and moved slowly between them. At two particular positions, sharp images are formed on the wall. The heights of the images ...
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### Why do Photochromatic lenses react to temperature changes?

So, I'm aware that Photochromatic lenses are affected differently due to different ambient temperatures. From what I've read it seems that the molecules rearrange their structures slowly in cold ...
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### Where do rays that are not marginal or principal get stopped?

The picture is from an MIT lecture but the concepts are explained in many optical texts. The chief/principal rays go through the center of the aperture stop, hit the edge of the field stop, and the ...
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### How is focal length defined for a two lens system?

I have found the formula for the effective focal length $f$ of two thin lenses with focal lengths $f_1$ and $f_2$ separated by distance $d$ to be $\frac 1f=\frac 1{f_1}+\frac 1{f_2}-\frac d{f_1f_2}$. ...
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### Rule sign for concave and convex lens?

I am just totally confused about the rule sign of convex and concave lenses. The general formula: $1/v-1/u=1/f$ Is okay but when solving problem sums sometimes $v$ becomes negative sometimes $u$ and ...
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### How to make the projected image smaller by adding one ore more lenses in front of the built in projector lense?

I have a projector that creates a large image, even if the distance to the screen is short. The device is very small, approximateley 10x10 cm if you look from above. The height is only 3 cm. I ...
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### Why do you need at least two rays to form an image?

Why isn't enough one light beam to form an image in your retina for example?
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### Covering half of a lens [duplicate]

What happens to the image of an object kept before a lens if the upper half of lens is covered by an opaque coating? I understand that the full image will be formed and only the intensity of the ...
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### Splitting an image in a lens into two sources?

Is it possible to project an image of light that passes into a lens onto two surfaces without affecting the image?