# 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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### Number of images formed by a convex lens

I came across a thought and (literally) am very vexed with it. My recreation of it is :- I know I am bad at drawing so forgive that. So, what I thought is that if we have a lens kept in vacuum, which ...
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### Using Thin Lens Equation to find how far 1972 Blue Marble photo was taken

I am having difficulty using the information I found in Optics Eugene Hecht to calculate how far away the 1972 Blue Marble photo (shown here) was taken. The camera used was an 80mm Hasselblad camera. ...
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### Can a concave lens be used as a eyepiece in refracting telescopes instead of a convex lens

Whats the harm if we use concave lens as eyepiece instead of another convex lens? We just need to make the foci of eyepiece and objective coincide.
1 vote
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### Thin Lens in different media

I have been given an equiconvex lens (of given focal length), placed on a plane mirror, with water between the lens and the mirror. An object has been placed at a certain distance and I have been ...
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-...
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### How to determine focal length from a lens specification

I'm working in a ray-tracing program that allows me to construct spherical lenses by specifying the radii of curvature for both faces, the lens radius, and the center thickness. I would like to ...
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### Is it possible to determine the magnification of a compound microscope given the objective focal length, eyepiece focal length, and objective di?

Question as stated above, I want to know if it is possible to determine the magnification of the microscope from the objective and eyepiece focal lengths, and image distance of the objective lens. ...
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### Can the eye lens not produce a virtual image when the object is between Focus and Optical Centre?

My teacher dismissed the question saying it is not possible for the eye to do so simply because we didn't know the focal length of the eye. That confused me. The focal length can vary, sure. When we ...
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### Luneburg lens in a medium

A Luneburg lens is a spherical lens with a gradient refractive index. It has the interesting property that light coming from focal length of infinity will be focused on the surface of the lens. The ...
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### How will Newton's rings look using a Concave-convex lens?

I want to examine lenses that are concave-convex (one for each side) using the Newton's rings method. I'm trying to build the theoretical model for this, but I'm quite sure that the rays of light will ...
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### Eye Floaters Optics

Eye floaters are these annoying objects floating in someones eye, usually seen by someone experiencing them as squiggly lines and dots buzzing around, either dark or partially transparent (I ...
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### Exit Pupil, Objective Aperture, Magnification, and Brightness

Why is it that for two pairs of binoculars, with equal aperture, the one with smaller magnification has larger exit pupil and results in brighter images? If I understand correctly, the aperture ...
1 vote
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### Optical projector that reduces image size

I'm starting to wonder if this is not possible. I have built a projector to project UV light, through a monochromatic mask [a black & white 2x2 film negative] onto a target. The image on the film ...
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### What is the function of a concave lens in a laser pointer?

In my cheap laser pointer I found a concave lens in front of the LED. I expected a convex lens. If I remove the concave lens the beam is much less collimated. The same if I replace the concave lens ...
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### Intuitively understanding virtual images in a multi-(thin)lens system

Let's say there is a multi-lens system of a converging lens (ex. a biconvex) and then a diverging lens with an object on the left of the system. And furthermore, let's say that due to the specific ...
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### Can we see real images with lens? [duplicate]

There was this question. In an experiment to determine the focal length of a convex lens, a student obtained a sharp inverted image of a distant tree on the screen behind the lens. She then removed ...
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### How to Calculate Focal Length when in another medium?

How do you calculate the focal length of a lens when it is placed into another medium, if I only have the focal length of a lens in the air? I understand that the lensmaker's equation should be used, ...
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### Is image projection a good test quality for hyperopia glasses?

I've just bought a new pair of glasses for hyperopia, and want to test the lens quality. If I use the lenses just like a magnifying glass, to project the image of a lamp onto a wall, the image should ...
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### What is the apparent location of a real image formed by a lens? [duplicate]

Let's say I place a tennis ball 1 m in front of a plane mirror. The mirror will form a virtual image of the tennis ball, and if I look in the mirror, it appears to me that there is a tennis ball ...
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1 vote
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### Best High Zoom Lens Configurations [closed]

Just wondering which lens configurations are usually best or most optimal for achieving high zoom in the smallest space or with fewest lenses. E.g Let's say we want to achieve a 1000x magnification. ...
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### What is a convex-concave lens?

I came across this term while studying for optics, and I'm unsure as to what this means. My thinking is that it might be a meniscus lens, but the text separately give two different models for each ...
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### Spherical aberration of lens

Why is spherical aberration absent in an image formed by a plano-convex lens on its principal axis? Will it be present in other types of lenses?
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### How to find the image field of a Gaussian beam impinging on a positive lens? I am trying to calculate the impulse response and find the image field

How to get the image field for the setup in the following question , where a Gaussian beam is incident on a positive lens with focal length f z0 and z1 are the object and image distance? Can anyone ...
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### Why is a bigger camera sensor better at low light than a smaller one?

People say a bigger camera sensor is better for light performance as the photo sensors are bigger and hence let in more light. But couldn't you just let the same light in and focus it down onto the ...
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### Lens maker’s formula from parabolic approximation

I’m attempting to derive the lens maker’s formula for a thin or thick lens using the parabolic approximation. I’m familiar with the other proof using the law of refraction and different angles. The ...
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### Formula for power of a lens submerged in a medium

I was always of the opinion that the power of a lens would invariably be the reciprocal of its focal length, irrespective of the medium surrounding it. However, I ran into a slightly different formula ...
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1 vote
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### Real image drawn in case of concave mirror is bit off

About I am trying to draw real image of object in front of concave mirror. Case is when object is lying on the Center of curvature. What I have done so far There are two rays A ray incident on the ...
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### Where is the final image located at in a compound microscope?

In a compound microscope, is there a standard as to where the final image should be located? After doing some research, I arrived at either the final image should be located at infinity (to be focused ...
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1 vote
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### How to find out the relation between liquid lens curvature and changing the focal point? [duplicate]

I have a question regarding liquid lens. how much we have to change the curvature to get an image shift of 30mm?
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### How do you derive the formula's for equivalent focal length and back principle plane for 2 thin lenses separated by a distance?

I've found online that the formula for the effective focal length of 2 lenses separated by a distance is: $$\frac 1f=\frac 1{f_1}+\frac 1{f_2}-\frac d{f_1f_2}.$$ However, I'd like to know how this ...
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### Is it possible to define the Point Spread Function for a lens?

I have seen several papers and reports in which the Point Spread Function (PSF) of a microscope is calculated and measured. In particular, as far as I understand, a light point source is placed in the ...
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### Multiple lens configuration thickness and distances

Struggling to understand where I should measure lens thickness and distance between lenses from. I've attached an example multiple lens setup. For determining individual lenses thickness is it simply ...
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### Printing 2d fresnel zone plate

Recently my teacher asked me to create a Fresnel zone plate (Fresnel lens to be accurate). I wanted to print it using a laser printer with a resolution of 1200*1200 dpi. I know that i should block ...
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### Lenses and missing reflection

I am wondering why reflected rays are not considered with lenses. If a ray strikes a surface, another is reflected off that striking point; however, this is not added when studying lenses, only ...
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### What are the equations for a 2D projection of the distortion induced by a cylindrical lens?

Imagine you have a cylindrical lens of power $C$ and of angle $\theta$ relative to some neutral 0 axis. I want to know, if you took a normal 2D image and shown it through that lens, what would the ...
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### Final image formation in these 2 cases:

Can someone please explain simply how we determine how many times we have to consider reflection and refraction to obtain final image. Example a: Here they only considered refraction twice to obtain ...
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### Visibility of objects when looking through a half-covered concave lens [duplicate]

If a concave lens is half-covered with a piece of a paper and used to look at an object, is the object completely visible or is part of the object not visible? (The person who closed this question ...
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### Using Fermat's principle to derive the Cartesian paraboloid

I am self-studying Optics by Pedrotti and I'm on the subject of geometric optics, specifically ideal Cartesian surfaces. These are reflecting or refracting surfaces that form perfect images. I was ...
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### Geometric optics multiple lens focal length calculation

Just wanted to understand how I would go about calculating the effective focal length of these different lens configurations. There's the combined focal length formula, but I'm struggling to apply it ...
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### Why is there no "parabolic abberation" in lenses?

I am trying to understand what an "ideal" lens would look like. Spherical surfaces are not correct, as these produce spherical aberration. This article here, is really useful. It 'derives' ...