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41
votes
6answers
6k views

Do people wearing glasses have different field of view than those who don't?

There is one thing I sometimes wonder about ever since I was a child. Do people who wear eye glasses see objects in different size than those who don't?(Technically different size means different ...
40
votes
5answers
5k views

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 ...
30
votes
6answers
15k views

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 ...
27
votes
3answers
159k views

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 ...
23
votes
1answer
10k views

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 ...
21
votes
5answers
8k views

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, ...
15
votes
3answers
2k views

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?
13
votes
6answers
16k views

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 ...
10
votes
3answers
1k views

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 ...
8
votes
1answer
962 views

Glass that only allows light of specific amplitude to pass through it

Is there a type of glass, mirror or lens that allows only lights of amplitude equal to or greater than a fixed value to pass/reflect through them?
7
votes
2answers
740 views

How do I find the right lens for my laser?

I purchased this line laser recently and I'm running into a bit of an issue. The laser shoots out at a 120 degree angle which is perfect. However, once the laser spreads to about 4.25 inches, I need ...
7
votes
5answers
420 views

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 ...
5
votes
2answers
2k views

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 ...
5
votes
2answers
5k views

how does a sniper scope work?

How does a sniper rifle scope enables us to pinpoint the exact location even though the lens in situated 5-6 inches above the muzzle. The bullet leaves the muzzle and hits the target exactly where the ...
5
votes
5answers
1k views

do lenses with curved focal planes exist

I know about spherical, aspherical, cylindrical lenses, but are there lenses that could have a curved focal plane? for example, the retina of the eye is curved, and still we see sharp images of ...
5
votes
2answers
106 views

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 ...
5
votes
1answer
227 views

Optics Paradox?

Imagine we have two lens, one convex and one concave, spaced in such a way that the convex lens is before the concave lens. Now each lens has its own focus length and both are spaced such that the ...
5
votes
1answer
83 views

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 ...
5
votes
1answer
367 views

Options to correct rectangular laser beam profile?

We recently switched to a 405 nm laser diode which has a terrible beam profile -- it is a well-defined rectangle with an aspect ratio of about 10:1. The image below shows the collimated beam which ...
5
votes
2answers
238 views

Smaller Airy disk with another lens?

Is it possible to reduce the airy disk size produced by one lens with another lens placed after the previous one? For example, parallel ray incident on first lens L1 (without aberration), then there ...
4
votes
8answers
976 views

Is there a lens that would invert my vision?

Would I be able to invert my vision by mounting a particular lens in front of each eye? I am currently able to achieve this by mounting a right-angled triangular prism across both eyes. The specific ...
4
votes
4answers
565 views

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.
4
votes
3answers
4k views

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 ...
4
votes
1answer
682 views

Compound lenses and virtual images

Ok so I have this problem where I have a system of two lenses. All I know is that the distance between the object and the first lens is 30cm, the distance between the object and the final image is ...
4
votes
2answers
434 views

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 ...
4
votes
1answer
166 views

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 ...
4
votes
2answers
5k views

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 ...
4
votes
1answer
209 views

On the optics of high-resolution surveillance drones

In this youtube video (which is an except from a documentation I believe) a DARPA development for a high-resolution surveillance camera is presented. This question is regarding the optics that are ...
4
votes
3answers
146 views

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 ...
3
votes
2answers
573 views

Arrow that changes direction home experiment

I saw this cool optical effect in a experiment on Youtube: https://www.youtube.com/watch?v=G303o8pJzls Could anyone explain to me why the arrow points in the opposite direction? I have read ...
3
votes
2answers
4k views

Radius of curvature and focal length

Is the radius of curvature of a convex or concave lens longer than the focal length of the lens? Does the center or curvature affect the focal point in a lens?
3
votes
2answers
602 views

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 $...
3
votes
1answer
2k views

Calculating minimum object distance for a lens

I am trying to figure out the Minimum Object Distance based on a simulation available here. In case you can't open it (it's a Java applet...) I'll describe it briefly. It shows an object emitting ...
3
votes
2answers
3k views

How to draw a ray diagram from focal length, object and image heights?

Q. An object of height 8 cm is placed in front of a lens. It's inverted image of height 4.8 cm is formed on the screen. If the focal length of the lens is 12 cm then by drawing at scale calculate the ...
3
votes
2answers
562 views

Effect of gas or liquid within a compound lens system

Hi my question is if a compound lens system if filled with gas or a liquid how does it affect the system when compared to the lens system being separated by air alone. Does this affect the focal power ...
3
votes
1answer
44 views

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 ...
3
votes
1answer
77 views

Easy method to measure the NA of a lens system?

I have a lens system made up of some components of the Leica Z16 APO zoom system. This includes a built-in iris diaphragm to adjust the Numerical Aperture (NA) and therefore the depth-of-field (DOF). ...
3
votes
3answers
2k views

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 ...
3
votes
1answer
3k views

How to find focal length of a single convex lens?

I need help finding the focal length of a single convex lens. The radius of curvature is 200mm. left side is air and the glass has a index of 1.5. I search on google but there was only formulas for ...
3
votes
1answer
736 views

Double image in binoculars

How can I reduce the double image seen when looking through binoculars? I recently got a new pair, but have been having troubles using them because I am seeing double...
3
votes
1answer
534 views

How does a flat wedge lens work?

I've been seeing this lens in a lot of places especially microsoft: http://www.youtube.com/watch?feature=player_detailpage&v=rJ1p5SD3sOM#t=45s http://blog.seattlepi.com/microsoft/2010/07/08/on-...
3
votes
1answer
41 views

Concave lens path of ray

What will be the path of ray passing through the first focal length of a biconcave thin lens kept in air? I know that a ray passing through focus or appearing to pass through focus of a thin lens ...
3
votes
1answer
356 views

Help calculating field of view for ball lens I just bought

I have a 5 mm (diameter) solid ball lens that I intend to place in front of a 36mm X 24mm camera sensor (I have already made preparations for the image to be focused and for the sensor to not be ...
3
votes
2answers
259 views

Proof that a spherical lens is stigmatic

In geometric optics, we generally allow that, for example in the case of a convex lens, rays coming from a particular point get refracted towards another particular point on the opposite side of the ...
3
votes
2answers
59 views

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 ...
3
votes
0answers
31 views

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 ...
3
votes
0answers
95 views

What does it mean for a Fresnel lens to have two finite conjugates?

I'm in a situation where I need to reverse engineer a product that my company already manufactures and sells, but it wasdesigned too long ago for anyone to remember. It uses a Fresnel lens with the ...
3
votes
0answers
25 views

Colour of artifacts in a lens flare

I'm adding a lens flare to an illustration; which got me thinking: Are the colours of the artifacts (hexagonal/circular) which appear in a lens flares purely random, or much like a rainbow (...
2
votes
3answers
1k views

What does the optical zoom in telescopes do?

How does the optical zoom works.. Does it brings the light closer to the object... Or Does it just enlarges the picture of the object. In other words... Suppose I have telescope with 1 light-year ...
2
votes
2answers
4k views

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....