Questions tagged [optics]
Behaviour and properties of light, and its interaction with matter, particularly in detection of light.
76
questions
2
votes
0answers
35 views
Telescope focal length, reducer and/or Barlow
Say I have a scope with a given diameter $D$, a given focal length $f$, and a given exit barrel diameter $B$. It has a maximum true FoV of $B/f$ (supposing $B<<f$).
Would adding a 0.5x focal ...
1
vote
0answers
55 views
How to chose a comfortable 2 inch eyepiece for a Skywatcher Dobsonian 150 mm f/8 reflector?
Totally newbie here. I got the Skywatcher Dobsonian 6 inch (150 mm) f/8 Newtonian reflector. I had a brief chance to test it yesterday when the skies here in Melbourne cleared a little bit. I was able ...
2
votes
1answer
51 views
What kind of halo is this?
My friend sent me a video of a kind of a halo phenomenon and asked me what kind of halo it is.
There is a 22 degree circular halo around the sun.
But there is also a ring which seems to go ...
4
votes
1answer
406 views
Have there been studies of “old photons” to see just how constant things like Planck constant has been?
The question Are photons aged? and answers therein have got me thinking:
I vaguely remember hearing something about experiments where "old photons" were collected by large telescopes from very ...
0
votes
1answer
63 views
Does this CHEOPS first light image imply bad astronomy?
@KeithMcClary's comment under lousy mirror corrected by software links to Bad Astronomy's First Light for the Exoplanet Hunter Mission CHEOPS Goes Tetrahedral which shows the image below.
I understand ...
2
votes
0answers
37 views
How often are wedge prisms used to correct chromatic effects of atmospheric refraction?
Atmospheric refraction (shown below) happens because Earth's atmosphere has an index of refraction that differs from unity.
@MikeG's comment mentions that this refraction would have a chromatic ...
6
votes
1answer
70 views
Voyager 1 and 2 detected a 20-fold increase in plasma density, significantly different refractive index?
As reported by Nature.com, Voyager 1 and 2 detected a 20-fold increase in plasma density going from the heliosphere out to interstellar space. Does that 20-fold difference in density imply a ...
3
votes
3answers
76 views
Optics: “Airy disc” and size of objects
Jupiter has a minimum brightness that is brighter than stars. Is the reason an “airy disc”, concentric rings as a diffraction effect, is seen around stars and not Jupiter because Jupiter has an ...
1
vote
0answers
31 views
Stellar aberration, any prism effect?
In stellar aberration, is there any prism effect, chromatic aberration?
0
votes
1answer
59 views
How can I determine if a typical low-end telescope is a refractor or reflector?
Is there a way to distinguish (with no manual, product info etc)?
8
votes
2answers
719 views
How exactly will DESI simultaneously capture individual spectra from 5,000 galaxies using optical fibers?
The BBC News article Telescope tracks 35 million galaxies in Dark Energy hunt says:
The aim of the five-year programme is to shed light on Dark Energy - the mysterious force thought to drive an ...
4
votes
1answer
359 views
Split telescope into two eyes
I am looking for an appendage to attach to the end of a telescope which splits the image into two eyes instead of one.
Does such an appendage exist?
0
votes
1answer
89 views
Questions about amateur astrophotographer Nik Szymanek's telescope
The 2011 Sixty Symbols video Spy Satellites (from Deep Sky Videos) shows amateur astrophotographer Nik Szymanek and his telescope.
Question: Can someone identify the model and design of this ...
1
vote
0answers
47 views
PSF magnification
I have a circular telescope pupil, a magnifying optic, and a detector. I am trying to calculate the point spread function as a function of wavelength. I am running into the issue that Python's 2D FFT ...
0
votes
1answer
77 views
Does anybody recognize this kind of prism?
Supplemental to this answer to Did Edmund Scientific 4¼ inch Newtonians have 90° prisms as secondary mirrors in the 1970's? I was poking around a bit further and ran across this "1960's Edmund ...
2
votes
1answer
46 views
Telescope focal point and inversion
When looking at a diagram of the optical path through a newtonian reflector, the lines always cross before the eyepiece. I understand that the eyepiece is used to focus this diverging light cone so ...
2
votes
1answer
133 views
Why are Shack-Hartmann sensors so expensive (4k+ USD)?
Recently I am searching for a Shack-Hartmann wavefront sensor for university laboratory usage. I was expecting my target sensor to be cheap, which is:
Low spatial wavefront resolution (50 x 50) for ...
16
votes
3answers
2k views
Why different specifications for telescopes and binoculars?
Sorry for the noob question but I don't seem to be able to find the answer on the internet.
I've been looking through some telescopes and binoculars and noticed that shops typically give different ...
1
vote
1answer
73 views
How are “parallel fields” implemented on the Hubble Space Telescope?
The Phys.org news item Hubble is the ultimate multitasker: Discovering asteroids while it's doing other observations mentions the Hubble Space Telescope's use of parallel fields:
A couple years ago, ...
1
vote
1answer
135 views
How to find the source of the light? [closed]
There are millions of galaxies out there in the entire universe. When a telescope is set to a direction to to identify the stellar objects, it can capture all lights from all the objects. How do we ...
2
votes
0answers
77 views
Why look at an infrared telescopes's mirror with ultraviolet light? (Herschel Space Observatory)
While link-clicking for Where did Herschel Space Telescope go in 2013? I ran across the 2009 Time Magazine article Two Telescopes to Measure the Big Bang which shows the file photo below with the ...
3
votes
2answers
112 views
What would be the obstacles to building a 6.5km space telescope besides cost?
In the comments of another question on this Stack Exchange site, I talk with another user about the possibility of building an optical space telescope with a 6.5 km aperture.
Obviously, this is much ...
2
votes
0answers
47 views
Within a given image of a multiple-image producing gravitational lens, does Fermat's principle apply?
The question Does gravitational lensing provide time evolution information? is excellent!
When we see multiple images of the same object because of the phenomenon of gravitational lensing, do all the ...
4
votes
3answers
242 views
Why does the Moon appear to be flat?
There's no way around it: when I look at the full moon at night it looks like a mostly flat disc, with at most a bit convexity in the middle. Phases of moon look like a full moon seen through a cut-...
6
votes
1answer
217 views
Angular diameter of the Sun's reflection from the ocean, seen from Sun-Earth L1?
I'm trying to understand how smooth the reflecting ocean surface would need to be to produce such a small bright spot as seen from the DSCOVR satellite at Sun-Earth L1. It appears to be only about 8E-...
3
votes
1answer
658 views
How does making a refracting telescope very long reduce the chromatic aberration of an uncorrected lens?
Below are two cropped views of "Johannes Hevelius's 8 inch telescope with an open work wood and wire "tube" that had a focal length of 150 feet to limit chromatic aberration." from ...
2
votes
3answers
212 views
How did Johannes Hevelius' long telescope work? Why all the round holes?
The drawing below, found in Wikimedia and at lib.harvard.edu is of a very long tubed aerial telescope. I believe it is taken from his 1673 work Machinae coelestis.
I've always wondered about the ...
2
votes
1answer
59 views
What are some formulas that are associated with the Schmidt corrector?
I want to fully understand how an SCT works. Thus, I figured out I can use some formulas that describe how an incident ray that is parallel with the axis would act after refracting off a Schmidt plate....
2
votes
2answers
396 views
What are the aberrations of an SCT? And how can they be eliminated?
The Schmidt-Cassegrain telescope is amazing! It is compact, suitable for astrophotography ,and it requires little to no collimation. However, the SCT has some inherent optical issues. What are they? ...
1
vote
1answer
121 views
Why aren't corrector plates aligned with the center of curvature in an SCT?
According to wikipedia, Schmidt corrector plates must be aligned with the center of curvature to eliminate the spherical aberration. However, in compact SCT designs by Celestron and Meade, that is ...
3
votes
3answers
348 views
Advice on first Telescope (refractor vs reflector), Barlow lens
I am planning on buying my first telescope. I am getting an 80mm refractor and a 114mm reflector for the same price range. Which would be a better option? Further, would a Barlow lens solve the ...
3
votes
0answers
200 views
Are they really sure this isn't an Airy disk? How was that ruled out?
How do they know that this is a spherical shell of gas, and not just something like an Airy pattern-like artifact produced by the VLT's large interferometric aperture?
Image from: https://www.eso.org/...
2
votes
0answers
49 views
Does Arecibo's secondary optics compensate aberrations when viewing farther away from vertical?
In the beginning of the short YouTube video Arecibo Uncut: Under the Dish with Phil Perillat it is mentioned that while dish antennas are usually a parabola, the problem is that a static parabola ...
2
votes
2answers
144 views
Arago Spot in the Shadows of Celestial Bodies
Recently, I've watched this video by Veritasium describing Poisson's Spot, or the Arago Spot. It is explained in the video that near circular (or spherical) objects can produce this optical effect, ...
3
votes
1answer
155 views
What is the cause of all of these sharp, concentric rings around bright stars in this HST image?
ESA's HST page heic1819 — Photo Release; Hubble reveals cosmic Bat Shadow in the Serpent’s Tail is of course beautiful and stunning, but my eyes are drawn to the diffraction artifacts of the bright ...
0
votes
1answer
143 views
Why does the sun appear 13x bigger through diffraction in Voyager 1 image from 1990, but not from Earth? [closed]
The sun in the Voyager 1 photo here from 1990 appears 13x bigger than its diameter, diffraction of course. On Earth, photographs of the sun do not make it appear 13x bigger. Why?
A description of the ...
6
votes
1answer
158 views
Why are there optical differences between sunrise and sunset?
I've noticed that sunrises are not reverse sunsets regarding the sky hues and lighting.
Sunrises always start pinkish and end with a glorious yellow sunshine.
On the other hand as the sun sets ...
7
votes
4answers
365 views
Where exactly is the modification that first corrected the spherical aberration in Hubble's primary mirror?
The April 2015 CBS News article How NASA fixed Hubble's flawed vision - and reputation describes the modification taken to the Hubble Space Telescopes by the Space Shuttle that was used to correct for ...
11
votes
3answers
789 views
Has anyone ever tried to make a simple telescope using ice?
I grew up with long cold winters, and saw a lot of remarkably transparent ice formed by refreezing meltwater, both in puddles and ponds, and in large icicles. I'd always thought about making optical ...
3
votes
1answer
208 views
What is a pupil slicer, and how does it work with anamorphic optics in VLT's ESPRESSO Echelle spectrograph?
This excellent answer points to ESPRESSO, - Echelle SPectrograph for Rocky Exoplanets and Stable Spectroscopic Observations. From there I looked at the Instrument Description and Performance page.
...
0
votes
1answer
255 views
Why does the sky look like it has three suns in this video? [closed]
Check out @natalie9280’s Tweet:
long story short, friday morning at around 6:40am i looked outside and i saw three suns.
i checked to see if there was an eclipse and i could[n't] find anything.
...
3
votes
1answer
108 views
How to understand Kepler telescope under large aspherical wavefront
To my understanding, a Kepler telescope is designed to conjugate one plane to another. For example scale down/up the incoming wavefront onto a wavefront sensor for measurement. It works well for small ...
2
votes
1answer
164 views
Telescope and its construction
I want to build a reflecting telescope in my home. I've attached a drawing of my plan that contains some explanations of what I understand so far, and highlights the parts of the design for which I ...
3
votes
0answers
52 views
Is it possible to model a solar thermal concentrator using Zernike polynomials?
This question might seem a bit off-topic, but I guess there are a lot of people here that know about optics, telescopes, etc.
I would like to simulate solar thermal systems that focus solar ...
2
votes
1answer
72 views
How well can the Sun's surface be resolved by an observatory?
There's no lack of photons, how well could a telescope resolve Sun spots and other surface features of the Sun? How would a high resolution Solar (space) telescope differ from for example Hubble which ...
9
votes
4answers
383 views
Are there any mirrors in space?
We have encountered galaxies that act as lenses, magnifying the light coming from behind them. This is super fascinating and it makes me wonder what other optic tools we might have at our disposal.
...
3
votes
1answer
553 views
How do tip tilt mirrors correct distortion in adaptive optics?
I'm currently trying to learn about how adaptive optics correct the blurriness caused by atmospherical seeing effects. This is my current understanding of how adaptive optics works (trying to offer ...
3
votes
3answers
623 views
Projecting an image of the sun / eclipse
This might be an astronomy.stackexchange.com question, but I think it is more in line with a camera obscura.
During the last eclipse I didn't plan ahead and grabbed some lousy toy "spy" telescope we ...
2
votes
1answer
225 views
Why is this HST WFPC2 image so much fuzzier than the WFC3 image of the same field?
I was looking at the comparison of 2007 and 2015 HST images of the "disappearing" star N6946-BH1 in Phys.org's article Collapsing star gives birth to a black hole. The 2007 images is from ...
1
vote
1answer
142 views
What telescope is this, and how does it work?
In the excellent chemistry series of Periodic Videos' episode Amazing piece of metal (speculum) there is an interesting showing and discussion of Isaac Newton's first telescope.
At ...
