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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Virtual vs Real image
I'm doing magnification and lens in class currently, and I really don't get why virtual and real images are called what they are.
A virtual image occurs the object is less than the focal length of ...
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Why can you see virtual images?
In optics it is widely mentioned real images are projectable onto screens whereas virtual ones can only be seen by a person. Isn't that contradictory? I mean in order to see the virtual image it has ...
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Sign convention in optics
Why is the sign convention used in the derivation of the lens formula and yet used again when it is applied in numerical problems? Won't the whole idea of sign convention be eliminated if it is used ...
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Where is a good place to learn classical optics for high school competitions?
I need to learn basic optics for a high school academic competition. Does anyone know any good places, preferably free and online, to learn the basics of optics, like lenses, angles of incidence, etc.?...
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What are these rays that appear in photograph of sun?
In many images of light emitting objects we see such rays. Why do they appear ?
What is the math behind their number and direction?
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Compound microscope vs astronomical telescope
In compound microscope, we take such an objective lens which has small focal length. While in astronomical telescope, we take such an objective lens which has large focal length.
Why don't we use ...
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Interference at the focus of a convex lens or a concave mirror
Now consider parallel rays travelling towards the convex lens. After emerging they get converged at the focus. Won't this lead to interference between light rays? Practically it should but I would ...
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If a lens focuses all incoming light to a point, how do we get 2D images?
How do lenses produce 2-dimensional images, if a lens bends all incoming rays of light to intersect at the focal point? Shouldn't this produce a single dot of light on a screen placed at the focal ...
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Are Fresnel lenses widely used for solar electricity? If not, why not?
I was just wondering why Fresnel Lenses are not widely used in the production of solar electricity. Their use there would mean that you could produce heat within a fraction of a second, up to a few ...
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Is there a more accurate form of the mirror equation $\frac{1}{f}=\frac{1}{u} + \frac{1}{v}$?
In the mirror equation $$\frac{1}{f}=\frac{1}{u}+\frac{1}{v}$$
Q1: Are $u$ and $v$ the distances from the object to the mirror surface or the distance from the object along the principal axis to the ...
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Can spectacles converge sunlight to an extent that it burns the eyeball?
I need to know whether wearing spectacles can cause optical harm.
I saw a movie where one pair of glasses was placed on table exposed to sunlight, then the sunlight converged and focused to a point ...
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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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What can we deduce by the fact that mirrors cannot get a ray hotter than Sun's surface?
I think it is quite counter-intuitive that some lenses or mirrors focusing sunlight to a single spot cannot produce a temperature higher than Sun's Surface.
What could a scientist deduce from that ...
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How is focal length defined for a two-lens system, separated by a distance $d$?
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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Sign convention for mirror and lens formulas
I have just started learning optics at school and my teacher derived the lens and mirror formulas. While doing so, she applied the sign convention for $u$, $v$ and $f$ and arrived at the final ...
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Why does wet skin sunburn faster?
There is a popular belief that wet skin burns or tans faster. However, I've never heard a believable explanation of why this happens.
The best explanation I've heard is that the water droplets on the ...
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Why do convex lenses not disperse light like prisms, given that entry and exit points aren't parallel?
I understand that light entering a parallel block of glass at a non-90 degree angle will cause dispersion of colours within the block but that these will be refracted by the same degree upon exit so ...
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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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Ideal surface for a perfect lens
in this physics lecture, on slide 15-16, it is found that the ideal surface for a perfect lens (which maps a plane wavefront into a perfect spherical wavefront, i.e. which makes focus all input ...
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Why do nearsighted people see better with their glasses *rotated*?
If you are nearsighted (like me), you may have noticed that if you tilt your glasses, you can see distant objects more clear than with normally-positioned glasses. If you already see completely clear, ...
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What causes blurriness in an optical system?
The way I understand the purpose of a typical optical system is that it creates a one to one mapping between each possible incident ray and a point on a sensor plane. This is like a mathematical ...
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Diffraction by a lens
The fraunhoffer treatment of circular apertures yields a diffraction pattern of circles, with the first minimum (dark ring) at an angular radius of $\theta$ where $\sin(\theta)=1.22\lambda/b$, where $...
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Strength of moonlight
So I read this xkcd, and thought it was kind of cool. However, I showed it to my engineer father and physics undergrad brother and neither seem to find the explanation very convincing (though they ...
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Thin lens formula
Can someone help me or guide me how the thin lens formula:
$$\frac{1}{s_1}+\frac{1}{s_0}=\frac{1}{f}$$
can be proven?
I was trying to prove it on my own using similar triangles, only to fail.
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Deep confusion with conventions and signs in geometric optics
This is an equation given in my book.
The question is why have they used a negative sign on the LHS?
Now, if you try to derive the mirror equation with simple geometry, you get
1/v +1/u =1/f . I ...
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Lenses and wave optics?
We all have studied lenses in the framework of geometrical optics, but how do they work within wave optics? I figure that the topic is quite broad, but I would appreciate any hints, like which ...
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How does the eye perceive a real image?
Okay, so I'm trying to grasp how the human eye will perceive the real image created for example by a convex lens. Take the upper image in this picture for example.
If you were to place a screen at ...
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A half covered lens
Let's say there's an object in front of a convex lens. I have a piece of paper behind the lens at the right location such that it will the lens will form an image on the paper. The object is ...
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Radius of curvature of a lens
Is the radius of curvature of a lens correspond the the radius of the sphere in which the lens rises from?
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Newton's rings experiment
I have performed experiments in my college laboratory on Newton's rings to find radius the of curvature of the convex lens used. I always get a dark center. Is it possible to get a bright center? If ...
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Does a lens always act as a Fourier transform?
I understand that putting a lens behind an aperture at the distance 1f, it will "get" the diffraction pattern to appear in the back focal plane. In this case the FT of the aperture plane ...
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Working of liquid lens
we were recently introduced to the liquid lens in school, but i havent quite understood the working of it. I realize that the curvature of the lens is changed by some process, but i dont exactly know ...
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Calculate the distance between two points from iPhone Camera
I want to calculate the distance between two objects using an iPhone camera.
Suppose I'm standing with my iPhone 10 feet away from the objects. Now, I want to calculate the distance between those ...
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Why does aperture size affect depth of field in photography?
Why do small and big holes (the aperture) in a lens change the depth of field in the image? (if you have big hole you have smaller depth of field).
I wondered if I should ask this on photo....
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Why are the edges of the shadow so bright?
Today I noticed something while playing with my specs (having diverging lenses).
Have a look at it :
This is the shadow of my specs on the wall in sunlight. The region of the lens appears darker and ...
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Put a sensor at the focal length, behind, or in front?
My intuition tell me that at the focal length a convex lens all the light converges to a point. Following that logic, it would make sense to me that a camera chip would either need to go slightly in ...
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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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Bi-convex vs. plano-convex lenses
As I understand, less spherical aberration is obtained when a collimated beam is focused with a plano-convex lens as opposed to a biconvex lens. What would be a situation when a bi-convex lens should ...
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Plano-convex lenses
When the spherical side of a planoconvex lens is towards the source we will see reduced aberrations normally we use it for the beam collimation. When we use two planoconvex lenses configuration why we ...
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On unfocused images, their information content and possible restoration
So, when an image is out of focus the light of any given point of the object does not refocus exactly at one point on the screen, but is spread out around a region, such that the light of the image at ...
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Why do lens (convex) not introduce any path difference to light incident on it?
My understanding is that the top rays spend less time inside the lens where the speed of light is slow and the middle rays spend more time inside the lens so the time is kind of compensated . But I'm ...
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Formula for lens periscope
I want to build a periscope.
To my great surprise even after intense googling I could find little relevant information about periscopes anywhere on the internet.
Let's say I want to build a ...
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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 could ...
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What is exactly an ‘virtual object’? (From the point of view of lens maker’s formula)
Here’s an image from my textbook
It shows, how an image is obtained from a convex lens. The second and the third images, shows in depth , that how a convex lens behaves.
They say, that suppose ( in ...
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Why do focal lengths affect magnification?
For compound lenses, the image formed by first lens acts as the imaginaryobject for the second lens.
In telescopes, the objective lens projects an image on its focal point which works as the object ...
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Optics, lenses and our eyes
When we view an image, is the focal point of our eye on our retina? Shouldn't that hurt?
Also, if that is how our eye works, then why don't lenses put the focal point their equivalent retina? I was ...
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How does a Galilean telescope form an enlarged image even though it has a diverging lens?
I have been reading about Galilean telescope and the picture in the book is something like this:
After rays pass through the converging lens, there is a real image formed which is intercepted by the ...
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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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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 temperature can I reach using magnifying glass at night?
What about full moon night and what about the night without moon?
Let's say in both cases we have no clouds and +25C air.
How big should the glass be to burn the paper? ant?
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