Questions tagged [optics]

Behaviour and properties of light, and its interaction with matter, particularly in detection of light.

Filter by
Sorted by
Tagged with
1
vote
2answers
31 views

Are telescope eyepieces ever made with a diopter adjustment (similar to DSLRs)?

I am learning about eyepieces, and "eye relief" and what sorts of eyepieces an amateur may want for their purposes, and was wondering if there are eyepieces with diopter adjustments, or if, ...
24
votes
4answers
7k views

Shouldn't this cause a fire?

This website shows a telescope projecting the sun onto a blackboard: https://astronomyconnect.com/forums/articles/2-three-ways-to-safely-observe-the-sun.21/ Why isn't the board catching fire? You ...
0
votes
1answer
73 views

How to make a 65 cm lens with a 20 cm hole in it for a Hamiltonian telescope?

This answer to What (the heck) is a Hamiltonian telescope? Is this one? confirms that the telescope in the question linked there is indeed as described and that the first lens is a full 65 cm aperture ...
1
vote
1answer
126 views

What exactly is a Hamiltonian telescope? Is this one?

This comment on the current answer to Why is this telescope so short? How hard is it to make such a fast primary? says In this forum topic Borisov appears to call it an f/1.5 Hamiltonian. Wikipedia'...
0
votes
0answers
17 views

Deciding optical factors between a refractive and reflective space telescope optics as a function of aperture? (visible light)

Reading Yale News' Lighting a path to Planet Nine: To detect objects that are otherwise undetectable, Rice and Laughlin employ a method called “shifting and stacking.” They “shift” images from a ...
1
vote
0answers
17 views

What are Native coordinates in the World Coordinate System?

i am writing my first paper about our solar telescope, and i need to explain the optical transformations in terms of World Coordinate Systems. I am not sure if i got the following right, and would be ...
2
votes
0answers
35 views

How did Michelson measure the diameters of jupiter's moons using optical interferometry?

In Betelgeuse: How its Diameter was measured (Chant, C. A., Journal of the Royal Astronomical Society of Canada, Vol. 15, p.133, Bibliographic Code: 1921JRASC..15..133C) the author says: The paper in ...
1
vote
2answers
113 views

Eyepiece::Astromania or Meoptex

I am looking into getting a zoom eyepiece for myself, and not sure on what basis to evaluate and compare various options. For some background on the type of observing I plan to do see my earlier ...
4
votes
2answers
83 views

What's still needed before we can observe orbits of exomoons thereby weighing exoplanets?

Comments below this answer to How do we weigh a planet? point out that we currently cannot (or at least have not) detect moons around exoplanets, much less measure the sizes and periods of their ...
2
votes
2answers
147 views

Why does this large Newtonian telescope's front cover have two or three holes in it?

The Michael Bernardo video How to use an Equatorial Mount for Beginners shows a large Newtonian telescope on an equatorial mount. The cover of the telescope's large aperture shows what looks like ...
5
votes
0answers
72 views

Point spread function image deconvolution

I would like to deconvolve an image of Saturn. I took an image of Saturn: Stack of 50 frames, the angular resolution of the original frames is 1.6''/pixel and the frames are scaled x4 before stacking....
1
vote
2answers
60 views

What are the effects of using non-spherical lenses in refracting telescopes?

Non-spherical (or non-circular) mirrors for reflecting telescopes are common and discussed in many places... But what about elliptical, parabolic or hyperbolic lenses?
3
votes
0answers
78 views

A simple echelle spectrograph for viewing solar spectrum

On the Astrosurf website here, someone has designed a deceptively simple echelle spectrograph for viewing solar spectrum. Briefly, light from an optical fiber falls on an echelle grating and which is ...
4
votes
3answers
263 views

What is it about the layout of the three gratings in a Bahtinov mask that makes its indicate focus in this way?

The question Lucky imaging with Celestron 14 - is this result reasonable? includes a beautiful example of a focus test using a Bahtinov mask and the image below from Deep Sky Watch's Home Made ...
3
votes
1answer
106 views

Can a telescope ever increase the apparent luminance of an extended object?

From what I know about common telescope designs, telescopes don't increase the apparent luminance of extended objects compared to the luminance seen with the naked eye. In this sense extended objects ...
3
votes
0answers
57 views

Precise meaning of collimation/alignment of a binocular

My question is about what exactly is meant by a binocular being collimated/aligned. I'm familiar with optics in general, but not with the nitty gritty of binocular design. There are various resources ...
2
votes
0answers
41 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 ...
3
votes
1answer
177 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
67 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
415 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
79 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
42 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
72 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
148 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
62 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
727 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
444 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
92 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
53 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
101 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
78 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
197 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
87 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
137 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
79 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
117 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
50 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
269 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
249 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
863 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
235 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
78 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
650 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
146 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
655 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
220 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
50 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
235 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, ...