How does telescope function

By: Craig Freudenrich, Ph. Amateur telescopes fit somewhere in between, and even though they are not nearly as powerful as the Hubble, they can do some incredible things. For example, a small 6-inch centimeter scope lets you read the writing on a dime from feet 46 meters away! Why can't you see an object that is far away? For example, why can't you read the writing on a dime when it is feet away with your naked eyes? The answer to this question is simple: the object does not take up much space on your eye's screen retina.

If you want to think about it in digital camera terms , at feet the writing on the dime does not cover enough pixels on your retinal sensor for you to read the writing. If you had a "bigger eye," you could collect more light from the object and create a brighter image, and then you could magnify part of that image so it stretches out over more pixels on your retina.

Well this is also only partially true, because a telescope that does not collect more light than your unaided eyes is just as useless as one that does not magnify. But, too much aperture some believe this to be an oxymoron! There obviously needs to be some kind of happy medium, where the aperture and magnification are balanced and work with, instead of against, each other. In fact, the two depend on each other.

In virtually all telescopes, the focal length remains fixed, so you vary the magnification by using eyepieces with different focal lengths. Before we go on, we need to talk about the exit pupil. The exit pupil is what we call the small disk of light coming out of the eyepiece. The diameter of the exit pupil is dependent on the aperture and the magnification, in particular:. Lower magnifications produce a larger exit pupil, and higher magnifications produce a smaller exit pupil.

From a practical standpoint, there is a highest magnification you should use, for the reasons outlined above. As a general rule of thumb, the upper limit is about 50x per inch of aperture. The rate is also faster for bright background, when gain in limiting magnitude can approach half of the nominal change darkening of the background within a range of several magnitudes.

With dark sky background, the gain can be less than half as much for the same nominal change in background brightness most of this effect is likely caused by the background brightness falling below perception threshold of the eye. This implies that higher magnification mainly compensates for the limiting magnitude loss due to light-polluted sky. Both, telescopic and naked eye limiting magnitude are affected by atmospheric absorption.

It is on average 0. Limiting magnitude around zenith is, on average, over 1 magnitude fainter than close to horizon. Graph at left shows the approximate change in absorption with zenith angle for selected wavelengths spanning the visual range h, g, F, e, C and r spectral lines correspond to , , , , and nm wavelength, respectively.

Other factors also influence limiting magnitude of the telescope, but their significance is relatively small. Eye transmittance directly affects the naked eye limiting magnitude value, and insomuch the limiting magnitude in a telescope. Thus, in otherwise identical conditions, it can vary up to 0. In other words, what is, say, 5-magnitude sky for you, may be slightly better than 4-magnitude sky for someone else - or the other way around.

This assumes identical pupil opening; different pupil size will either increase or reduce the difference in perceived brightness due to transmission. How does the telescope help us today? How did the reflecting telescope impact society? Who first described the first refracting telescope? Which lenses are used in telescope?

Which lens is best for telescope? Which telescope lens is stronger? What eyepiece is best for the moon? What does 50x magnification mean? What is the power of magnification? Previous Article What is the definition of self-esteem? Next Article What does the jolly green giant look like?