How a telescope works?

[undefined]

Ok. Here is an elementary question.

When hubble or any other telescope is looking at an object is the light the telescope observing actually from the furthest distance the telescope can view or is the telescope magnifying the light which is directly coming into the telescope?

I hope this question is understood.

[HypothesisTesting]

The light is coming from the distance to the star. For example, a star 4 light years away, the light is from that far. For a distant galaxy, the light is as far as that galaxy, like 13 billion light years. But that light left the star years ago.

The telescope first gathers the light which came to earth from that star . It only gathers the light that has actually arrived at the telescope. the bigger the diameter of telescope, the more light it gathers.

Then this collected light is magnified to make it bigger in angular size in an eyepiece.

[JustAFriend]

Strictly speaking, a telescope cannot magnify light.

The large area of the curved mirror concentrates a large number of light photons into a smaller space at the focus....

[Jens]

If you understand what eyeglasses or magnifying glasses do, then you understand what a telescope does, because it's basically doing the same thing.

[RickJ]

A telescope works exactly the same as your eye. A lens focuses the light on a sensor (retina in the case of your eye, a CCD in the case of Hubble). Only real difference is size. Your lens is about .007 meters in diameter and it projects .017 meters to your retina. That tiny lens coupled with a short distance to the retina gives a low magnification and a rather poor ability to see faint things as well as fine detail. To see fainter things you need a larger lens to collect more light. To see smaller detail you need a longer distance between the lens and its focal point the retina or CCD, as well as a larger lens. This is what the telescope does. It uses a larger lens, 2.4 meters in the case of hubble, and a longer distance between that lens and the focal point, 57.6 meters in Hubble's case. Since your eye opens only about .007m Hubble collects (2.4/.007)^2 = 117,500 times more light than your eye. The resolution of the human eye is quite variable from person to person. Using 180 seconds of arc for the human eye, Hubbles larger lens lens plus longer focal length allows a resolution of about .08 seconds of arc or an increase of 2200 times. Actually its focal length is too short for the resolution of its CCD's and it could resolve detail half this size with double the focal length or half size cells in the CCD. This though increases exposure time hence the trade off.

In short a telescope is just a giant version of the human eye.

[Amber Robot]

Hubble uses mirrors not lenses, as do all professional telescopes these days.

[RickJ]

A mirror is a type of lens. My dictionary defines a lens as "a device that causes radiation to converge or diverge". This can be done by many means. A transparent lens is one. A reflective one another, but they can be magnetic (focus of a tube type tv for instance or an electron microscope) or by reflective incidence (X ray telescope) for instance. Also it can be a combination such as the Mangin which is both a transparent and reflective lens (both are negative -- diverging).

For the question it matters not if the main lens is reflective or refractive.

Rick

[ctcoker]

That is not how instrumentationalists, or opticians, or anyone else I know of that works with optics define a lens. Amber Robot is correct, a lens is a purely refractive device.

In addition, the only dictionaries I could find that used your exact definition were medical dictionaries (or Merriam-Webster), and even then, they usually first defined a lens as a transparent refractive device. So no, mirrors are not lenses.

[ravens_cry]

Don't argue the dictionary, folks. Isn't that one of the rules around here?
The point is, a rightly curved mirror and the right kind of lens do the same thing, concentrate photons.