1
vote
1answer
114 views

Magnification of an astronomical telescope not in normal adjustment?

I am stuck on this question: A telescope consists of two thin converging lenses of focal lengths 100cm and 10cm respectively. It is used to view an object 2000cm from the objective. What is the ...
14
votes
2answers
2k views

Is it possible to 3D print a mirror to create a high quality telescope?

Is it possible to 3D print a mirror with todays available materials? If so, would there be a reduction in image quality?
4
votes
2answers
100 views

Optically thick media

What does "optically thick media" mean? Does this property depend on the length of an enclosure? Why is the diffusion approximation for the radiative transfer equation applied to optically thick ...
2
votes
2answers
118 views

Can a point source be located more accurately out-of-focus or in-focus?

Let's say I am taking a picture, and I know a priori that the image is of a single ideal point source of light at infinity. With a perfect imaging system in focus, the image shows an Airy disk. I ...
2
votes
2answers
94 views

How to produce a loss-free combination of two “identical” beams?

This is for anyone with experience in optics/imaging/photography as well as anyone who likes to puzzle over tricky physics problems. As the title suggests, this is about combining two (for all ...
6
votes
6answers
406 views

Is antumbra part of shadow darker than penumbra part of shadow?

I'm exploring different types of shadows casted by objects. I want to know if antumbra part of a shadow is darker than penumbra part. I've found two misleading pictures on Wikipedia: First: Second: ...
1
vote
0answers
47 views

When viewed from a telescope, does an object get more magnified if its angular diameter is increased?

and if yes, how can the diameter be increased? Lets say I want to view saturn from a small telescope. Increasing the angular diameter will give a better magnification if the answer to the above ...
0
votes
2answers
86 views

Length of solid part of object shadow

Little background first: I take part in preparing environmental reports for wind turbines/farms and now I'm exploring shadow flickering effect of moving blades. From some sources (in Polish) I got ...
0
votes
0answers
72 views

How to calculate max/min Right Ascension and Declination in telescope field of view

I have a telescope with focal length 1200mm. My camera has 5184x3456 pixels with size 4.3um. This combination should give me a resolution of 0.74"/pixel and thus a field of view of 1.06° x 0.71°. ...
10
votes
2answers
2k views

Amateur moon laser ranging

Questions first, then my rough estimations: 1) Is it possible to perform moon laser ranging with amateur motorized 114mm telescope? My calculations suggest that for 1mJ laser it should receive ~2 ...
10
votes
4answers
836 views

How big should a lens of a telescope be so we can see the American flag on the Moon from the Earth's surface? [duplicate]

How big in diameter should the lens of the imaginary telescope to be so we can see the American flag from e.g. some observatory in Hawaii?
3
votes
0answers
112 views

Maximum-Entropy Method deconvolution implementation?

I am looking for an implementation of the Maximum Entropy Method for image deconvolution, ideally in MATLAB or Mathematica. I'm trying to reconstruct an image from fringe visibilities, as is often ...
5
votes
0answers
173 views

Suntan: UV absorption vs daytime

I guess that these questions were being asked by many people on the Northern Hemisphere during this summer (and other summers) and someone may give a nice, coherent answer. The general question is how ...
19
votes
2answers
649 views

Optimal telescope size?

Consider a diffraction-limited telescope with unobstructed aperture $D$. Such a scope is capable of yielding an angular resolution $\alpha$ that scales as $\lambda/D$, with $\lambda$ denoting the ...
10
votes
2answers
258 views

Why does a blue sky at dusk appear nearly black through a telescope?

Earlier this evening I was looking at the Moon through my cheap toy telescope (x150 magnification) when I noticed a (rather mundane) optical effect I couldn't explain. The Sun had just dipped below ...
4
votes
1answer
241 views

Future space-based telescope array

Radio-telescopes (e.g. the Very Large Array (VLA)) can simulate one gigantic dish by using separate smaller dishes. Q: Could such an array of optical telescopes potentially see an exoplanet at say 20 ...
3
votes
3answers
103 views

Quality loss when adding more components to a telescope?

I would think this would be inherently true, but I'm curious: (Assuming the highest quality amateur instruments are used.) Is quality lost when, say, adding a T-mount adapter, diagonal or any other ...
13
votes
4answers
715 views

Is there a limit to the resolving power of a mirror telescope?

Like, if you hammered out the asteroid 16 Psyche into a 1 mm thick iron foil disc telescope mirror with 2.4x the radius of the Sun, could you resolve details on the surface of an exoplanet? At what ...
14
votes
4answers
322 views

How far would you need to displace your eyes to get meaningful depth perception of the stars?

The question follows from xkcd cartoon "Depth Perception (941)". I've isolated the frames that describe the concept here. In words, one could theoretically point two cameras at the sky, and ...
4
votes
5answers
985 views

Are telescopes with a concave lens useful for astronomy?

Are telescopes with a concave lens (instead of convex ones) ever useful for astronomy? And if so, where are they used? Do they ever affect resolving power?
3
votes
2answers
23 views

For resolving different objects, are there any alternative coefficients to the one used in the Rayleigh criterion? (which is 1.22)

http://en.wikipedia.org/wiki/Angular_resolution#Explanation It's the point where you can't distinguish between the maxima and the first minima. But could there be cases where you have a more ...
9
votes
1answer
657 views

Why is the Ritchey–Chrétien telescope preferred in professional astronomy?

Hubble, as well as numerous other professional telescopes, use the Ritchey–Chrétien design. What optical and instrumental advantages does this kind of telescope have for professional astronomy?
6
votes
2answers
292 views

What makes a good set of binoculars? [closed]

After trying a bunch of binoculars at Star Parties and the like, I have a pretty good feel for about what aperture and magnification I'd like in a new set binoculars. I'm an eyeglass wearer so a long ...
22
votes
3answers
1k views

How to determine what size telescope to buy

A couple of years ago my son showed an interest in astronomy and we bought a 6" reflector telescope. We use it pretty regularly and have enjoyed it immensely. Lately we've both been wishing we had ...
6
votes
2answers
593 views

Optimal Angular Field of View (AFOV)

Given the rather huge price differences between eye pieces at the same focal length. How exactly does the AFOV affect the view seen through the eyepiece? Are higher / lower AFOV better for certain ...
7
votes
1answer
91 views

What is a backlit CCD sensor, and why might I prefer it to other kinds?

I've heard Astronomers talking about backlit CCD sensors, and talking about how much better they are than other types. What are they, why might I want to get one, and what are the pros/cons of this ...
15
votes
3answers
2k views

Observing lunar lander and footprints on the moon?

After Apollo 11 first landed on the Moon in 1969, there have been conspiracy theories that this never really happened and that it was all a hoax. In 2010 NASA released photos from its Lunar ...
2
votes
2answers
58 views

What objects look best in an O-III filter?

I've heard that an O-III (Oxygen III) filter is great for planetary nebulae. Is this true for all planetary nebulae, or just some or most? What other target types are often improved with an O-III ...
10
votes
3answers
168 views

Why is M42 red in the pictures, but green when observed at the eyepiece?

I saw magnificent images of the Orion Nebula (M42) in pictures from Wikipedia, However, when observed with a telescope, the nebula appears green hued, and I can't see any of the characteristic red ...
11
votes
4answers
5k views

What does f/4.6 mean in a telescope and how important is this value? [closed]

In some specifications for telescopes, I saw a value marked as f/4.6. What does it mean exactly, and how important is when it comes to choosing a telescope?
3
votes
2answers
3k views

Glycerol: refractive index & absorption spectra in 0.2-0.4um range

Could anyone suggest where can I find absorption spectra & refractive index of Glycerol? I am specifically interested in UV range, 200-400nm, everything I was able to find out was for standard ...
5
votes
4answers
760 views

Optical explanation of images of stars?

Very often when viewing pictures of the cosmos taken by telescopes, one can observe that larger/brighter stars do not appear precisely as points/circles on the image. Indeed, the brighter the light ...