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Questions tagged [lenses]

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problem of spherical refracting surfaces [on hold]

A glass sphere has radius R=5cm and index of refraction 1.6 When viewed through the paperweight, how far away does the tabletop appear to be to the observer?
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2answers
31 views

Image formed via a converging lens when the object is placed at focal point

In the case where the object is placed at focal point F of a converging lens, the rays of light (the one passing through O and the one sent parallel to the principal axis never meet) so I am assuming ...
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Finding the principal plane of a spherical lens with radius R

For an experiment I will be using this equation for a compound lens: $\frac{1}{f} = \frac{1}{f_1}+\frac{1}{f_2} - \frac{d}{f_1f_2}$ $f_1$,$f_2$ are the effective focal lengths and $d$ is the ...
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16 views

Focal length of a Plano-convex lens [closed]

Question A Plano-convex lens has a thickness of $4 cm$ when placed on a horizontal table with the curved surface in contact with it. The apparent depth of the bottom-most point of the lens is found ...
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3answers
55 views

Can a lens be used at radio frequency?

Lenses and Antennas are two means of manipulating EM waves. While antennas are predominantly used at RF / Microwave frequencies, Lenses are used for optical/IR regions of the spectrum. I understand ...
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1answer
36 views

The electric field in the focal length of a strongly focused lens

I have a Laguerre Gaussian beam and I want to focus it by using a strongly focusing lens. But my question is that I don't know what will happen to the electric field structure in the focal length ...
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1answer
19 views

Raise index of refraction of spherical lens

What happens to focal length and aperture of a spherical lens if you raise the index of refraction of the glass?
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1answer
47 views

Why don't we use sign convention during the derivation of a lens maker formula?

Please have a look at the lens makers formula: http://www.quantumstudy.com/physics/ray-optics-15/ In any derivation of Geometrical optics, we use the sign convention twice: once while deriving it ...
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11 views

A good reference for optics and lens systems? [duplicate]

I want a suggestion for a good reference/handbook for optics and optical system with lenses. For example, a book where confocal microscopy is present but the confocal geometry is described in detail.
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4answers
37 views

What does the intensity profile of a set of parallel rays look like after travelling through a convex lens?

I have had a discussion at my university about the following question. Imagine a 'perfect' convex lens and a set of parallel rays, falling onto that lens. The set of incoming rays has a flat intensity ...
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1answer
83 views

What happens if we cut a convex lens horizontally?

Does the focal length change? Or does it remain constant and only the brightness of the image is reduced?
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1answer
49 views

Refractive screen for myopia [closed]

Is it possible to create a screen for a computer monitor to allow a Myopic person to see the screen without glasses?
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1answer
67 views

Looking through a glass hemisphere [closed]

I've found the following question on IsaacPhysics.org . I've been working on it for a couple of hours but I cannot figure it out. A looking glass is used to read an ancient scroll. This lens has a ...
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1answer
30 views

Principal focus question

On my notes İ have written that the definition of principle focus is : the point on the principal axes where rays appear to diverge or rays actually converge. However İ was looking at this diagram of ...
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2answers
67 views

Question about lenses in the human eye

To see near objects,the ciliary muscles contract and the suspensary ligaments loosen,making the lense thicker. İ don't understand how that helps us to see distant objects . To see distant objects ...
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2answers
60 views

Does anti-blue coating work less effective on high power lens?

I purchased a spectacle from an online website with anti-blue coating. The features of this product is mention here. Once I receive it, I started using the product without testing the anti-blue ...
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3answers
40 views

How lens works in eyeglasses for distance and near vision?

Consider someone who wears a Contact Lens that is -10.00 diopters in power (very powerful) for distance correction, but needs +2.00 diopters ADD reading glasses "over-the-top" of the contacts to be ...
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2answers
54 views

Imaging resolution with laser

The transverse optical resolution of a lens, as determined by its point spread function, can be approximated as $w$ ~ λ/(2$NA$), where $NA$ is the numerical aperture and λ is the wavelength of the ...
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1answer
34 views

Magnification of Objective Lens

Where should we place an object to get 10x magnification with a 10x objective lens? we know that objective lens can be modeled with a simple positive lens so magnification should be dependent on the ...
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0answers
46 views

Effects of lenses

I have three convex lenses that I'm arranging so as to function as a crude magnification device. My question is about the image that I see. It seems that no matter how I arrange them, with respect to ...
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2answers
99 views

Why does shorter focal length result in greater beam divergence?

So I got 2 converging Fresnel lenses, one with 50 mm focal length and other 70 mm. My experiment looks like this: When trying to focus and SMD LED emitter into a narrow beam (sticking to lenses ...
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1answer
139 views

Newton's ring conceptual doubt

Newton’s rings are formed as a result of interference between light waves reflected from the upper and lower surfaces of the air film developed between the convex surface of the plano-convex lens and ...
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0answers
25 views

Is the object focus always on the same side as the incident ray in converging lens?

We know that representation of a lens is made up of the lens itself, the principle axis, 2 foci points (object and image focus) and the optical center. In my notes it says that in a converging lens ...
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3answers
60 views

Why do we need telescopes/ binoculars/ etc? [closed]

Why do we need to use magnifying objects to see things that are far from us? Why isn't the light coming from those objects enough for us to see without special aid? Is it because light loses energy on ...
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1answer
28 views

What refractive index should be used while calculating the focal length of lens using lensmaker's formula?

Suppose a lens is half dipped in liquid. Then should the refractive index of liquid with respect to air should be taken. Or should refractive index of glass wih respect to liquid be taken. Or perhaps ...
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1answer
67 views

Calculating pupil magnification

Is it possible to calculate pupil magnification, given that these lens parameters are known: focal length f-number at infinity focus positions of front and back principal points position of the ...
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1answer
49 views

Front/rear effective diameter on a camera lens

I'm in the process of trying to understand lenses a bit better so I decided to take a look at the specs of an actual lens I have access to: Kowa LM25HC (datasheet). Can someone explain the meaning of ...
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1answer
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Does entrance pupil diameter change with object distance?

Here is my current understanding of things, correct me if I'm wrong. Entrance pupil diameter effectively determines the light-gathering ability of a lens. It is related to the working f-number by the ...
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1answer
28 views

Thins Lens Equation Question

According to my textbook, it says that according to the thin lens equation, object distance and image distance vary inversely. However, when I do a converging lens simulation, as I increase the ...
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1answer
119 views

Sign convention for lens [duplicate]

What will be the sign convention for radius of curvature of a concavo-convex lens ? I know for equibiconcave and equibiconvex separately but for mixed one I am not clear . For example for the ...
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68 views

“3f system” - two lenses with the same focus

Lets assume we have a point source of light. In a distance of f after it we have a lens with focus f and a mask, and in a distance f after it we have another lens with focus f. Than we look at the ...
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1answer
4k views

How is a (rifle scope) reticle in focus?

The lens zooms and focuses something very far away, yet the reticle inside the lens assembly is in perfect focus just like the far objects. How?
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76 views

Lens designing and light splitting

months ago I started thinking about making a lense that will have special features - high FOV without fisheye effect. I have written a program that solved it for me, here is a preview - it increases ...
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0answers
21 views

How do I determine the lens to set the focal length of a converging or diverging beam?

I have a gaussian beam going through two lenses. The first lens is focusing a collimated gaussian beam to a focal point either before or after the second lens. What formula do I use to get the focal ...
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29 views

Geometric optics limit in lens design [closed]

What is the rule-of-a-thumb ratio of lens' thickness to wavelength at which they can be designed using ray optics approximation? (The thickness is more relevant to gradient index lens, homogeneous ...
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21 views

Will a combination lens have symmetric focal length on either side?

In this discussion on finding the focal length for combination lens, the image described in the answer shows the measure of focal lengths. Description of the Gullstrand equation also talk about front ...
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2answers
56 views

Focusing white LED light into a spot as small as possible

An aperture (about 1mm) is placed 2cm in fount of the LED, collimated by a f=50mm lens, then focused by a f=100mm lens into a 3x3mm spot. The focal distance of the second lens cannot be decreased. ...
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79 views

How do hypermetropic people see objects beyond the focus of their convex corrective lenses?

The way I have developed intuition about optics suggests that humans can only see objects if two rays of light that originally emanated from the same point reach the eye in a way such that when ...
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2answers
84 views

Depth of field of the human eye

When reading about the basics of photography and the physics involved, I learned about  depth of field. Long story short, the message is that with a smaller aperture, the length of the depth of field ...
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2answers
77 views

Difference in focus between lenses and glasses [closed]

I have both glasses and contact lenses. The prescriptions are both recent and up to date. I am 46, so I'm starting to have a harder time to focus on things that are very close to my eyes, compared ...
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0answers
37 views

Biconvex lenses in 2 media

The question is what is the formula of the focal length of a biconvex thin lens if object medium is water and the image medium is air. I know that we have: 1/f = (n-1)*(1/R1 - 1/R2) , if the medium ...
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24 views

Screen distort for corrective lens

Can we apply a screen distort for corrective lens for eye ware instead of using a lens maker? Just test at home with a phone screen and buy at shop. To reframe the question can we bring to effect a ...
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1answer
122 views

Focal length of Convex lens

Is it true that, twice the focal length of a convex lens is equal to the radius of curvature? Please give your opinion.
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2answers
63 views

What's the difference between these two approximations for thin lenses?

I have seen the thin lens equation, which describes the following relation. $$\frac{1}{\text{image distance}} + \frac{1}{\text{object distance}} = \frac{1}{\text{focal length}} \tag{1}$$ However, I'...
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0answers
87 views

Spherical aberrations: 2 Plano-convex lenses with suitable distance

" By using two Plano-convex lenses separated by a suitable distance: When the two plano-convex lenses are separated at a suitable distance, the total deviation is divided equally between the two ...
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3answers
48 views

Does density of light power (w/m²) increase after passing a convex lens ?

Does density of light power (w/m²) increase after passing a convex lens ? and if so i need the equation that represent that increase
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1answer
65 views

Can we see through the central obstruction of a lens?

I have a very basic question in optics inspired by this article from the University of Stanford which clearly states that one should see a light source through a mask in the middle of a lens if the ...
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1answer
27 views

For nearsightedness how does the concave lens not shift the focus point for near objects?

In case of myopia, the light focuses in front of, instead of on, the retina when observing far away objects. while for near objects the eye is able to focus the light onto the retina. For most people ...
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0answers
18 views

In this situation, is an endless sequence of images (theoretically) formed?

I was dealing with an optics problem, where an object is placed at $u= -60$ cm in front of a biconvex lens of radius of curvature $R=30$ cm and refractive index $\mu=1.5$ . Simple calculations show ...
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28 views

Conservation of radiant flux in imaging?

I've been deriving the imaging equation for irradiance on a photosensor in terms of the object radiance: $$ E(x,y)=\frac{1}{f^2}\int\!\!\!\int \, L(x,y,u,v)\cos^4\theta \, \mathrm{d}u\,\mathrm{d}v ,$...