All Questions
15
questions
1
vote
2
answers
189
views
Diffraction limit PSF and angular spectrum method?
I know from the angular spectrum method that given a field $U$ with a wavelength $\lambda$, we can decompose it with Fourier transform.
\begin{equation}
U(x, y,0) = \int \int {\tilde{U}_0(f_x,f_y)} ...
- 444
1
vote
2
answers
144
views
Why rays of light from different points don't form an image?
I'm asking a clarification about this questions:
Why does an image only form where light rays coming from a single point get reflected or refracted and converge to a common point?
I want to know if ...
- 338
0
votes
1
answer
53
views
Paraxial Rays and Coma
In these slides it is stated that:
Coma is an abberration that afflicts off-axis light bundles in a
similar manner to the way in which spherical aberrations affects the
axial bundles.
About Coma, my ...
- 1,319
0
votes
1
answer
327
views
Thin Lens as phase transformation
In Introduction to Fourier Optics, J. Goodman, Chapter 5, the lens is analyzed as a phase transformation due to its variable thickness on the transverse plane xy.
Under paraxial approximation, the ...
- 1,319
1
vote
0
answers
78
views
Fresnel lens safe viewing distance
I work for a summer camp, and we have a Fresnel lens that is roughly 18in x 24in. I'm writing a safety document for the device, and am attempting to find out the minimum safe viewing distance without ...
- 11
0
votes
2
answers
388
views
Which path does light take through a lens?
In the picture below, the three principal light rays are drawn refracting through the lens , forming an image on the other side. But which path does the light actually take? That is , if i place my ...
- 1,581
19
votes
4
answers
5k
views
How does a telescope make an image larger by shrinking it?
I saw these images of how a telescope works and it seems like it is shrinking the image down to the size of the eye. I don’t understand how that makes the image bigger. My thinking is that shrinking ...
- 383
5
votes
3
answers
3k
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 ...
- 594
1
vote
2
answers
3k
views
Does focal length of a lens change on changing the incident light frequency?
I was surprised to see my textbook having the following:
"The focal length of a lens does not change when Red light is replaced by Blue light"- as an incorrect statement.
Why would the focal ...
- 575
2
votes
2
answers
1k
views
Why does a Fraunhofer diffraction pattern appear on the focal plane of a lens?
How do implement the information that behind the aperture/slit/crystal plane there is a focusing lens in the Fresnel-Kirchhoff integral?
It seems that the solution is understanding the role of the ...
- 21
1
vote
1
answer
6k
views
Intensity of light after it passes through a convex lens [closed]
When a parallel beam of light falls on a convex lens and get converge to its focus, does the intensity of light change?
- 387
2
votes
1
answer
3k
views
Question about lens maker's formula
I am trying to follow the derivation of lens maker's formula from the textbook "University Physics", p.1133 (https://books.google.com.hk/books?id=nQZyAgAAQBAJ&pg=PA1133#v=onepage&q&f=false)...
- 1,135
-2
votes
1
answer
725
views
What wavelength of light is the term 'focal length' defined against? [closed]
Because different wavelengths of light are bent differently in a medium, the focal length ought to be different for each of them (which is why white light splits up into a rainbow). If I have a "25 mm ...
- 1,958
7
votes
2
answers
2k
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 ...
- 183
2
votes
1
answer
1k
views
How to calculate beam spread of a non-point light source via an aspheric lens
I need to determine the angle, or rate of divergence of light from a single aspheric lens when I place a non-point light source (e.g. LED array) at a given distance from the lens which is less than ...
- 21