what does a refracting telescope use to gather and focus light

How Refraction Works

Light travels through a vacuum at its maximum speed of nigh 3.0 × 10^8 m/s, and in a straight path. Calorie-free travels at slower speeds through unlike materials, such as glass or air. When traveling from one medium to another, some calorie-free will be reflected at the surface of the new medium. The light that continues through the new medium volition either speed up or slow downwardly depending on how fast it can travel through each medium. For example, light travels more quickly through air than through water. The refractive index of a medium is the ratio of the speed of light in a vacuum to the speed of light in the medium. The higher the refractive index, the more calorie-free is slowed downwards past the substance.

Alphabetize of Refraction for Some Common Substances

Substance	Index of Refraction
Vacuum	1
Air	1.0003
Water	1.3
Ethyl alcohol	1.iv
Ice	i.3
Glass	1.5
Diamond	2.4

If calorie-free enters the new medium at a correct angle to the surface, it will modify speed, but not management. If it enters at an bending, its speed and its direction will change. The management the low-cal takes depends on whether information technology travels faster or slower in the new medium. Imagine driving a car from smooth pavement onto a sandy beach. If you arroyo the beach straight on, the automobile volition slow downwardly, but not change direction. If the yous approach the beach at an bending, one of the tires volition be slowed downwards past the sand before the other is, and the car volition turn in the direction of the tire that touched the sand showtime.

Light follows the aforementioned same principle and bends towards the normal when traveling into a medium with a higher index of refraction, and away from the normal when traveling into a medium where it can become faster. In the diagram below, light is leaving air and entering drinking glass, so it bends towards the normal on the way in, and abroad on the way out of the glass.

Lenses

Lenses class images by refraction and are typically made of either glass or plastic. They are basis and then that their surfaces are either segments of spheres or planes. If a lens is convex or converging, it takes parallel calorie-free rays from a distant object and bends them and so that they converge to a single point chosen the focal point. The distance from the lens to the focal bespeak is called the focal length of the lens.

If a lens is concave or diverging, it takes parallel rays and bends them then that they spread out. The rays will then appear to originate from a indicate in front of the lens. This betoken is too called the focal point, and its altitude is measured in negative units.

Refracting Telescopes

The earliest telescopes, also as many apprentice telescopes today, utilise lenses to get together more than light than the human being eye could collect on its own. They focus the light and make distant objects appear brighter, clearer and magnified. This type of telescope is chosen a refracting telescope.

Well-nigh refracting telescopes apply two chief lenses. The largest lens is called the objective lens, and the smaller lens used for viewing is called the eyepiece lens.

Magnification

The size of an epitome produced past a lens is proportional to the focal length of the lens. The longer the focal length, the larger the paradigm. The brightness of an image from a telescope depends partly on how much light is collected by the telescope. The lite-gathering power of a telescope is straight proportional to the expanse of the objective lens. The larger the lens, the more than calorie-free the telescope can gather. Doubling the diameter of the lens increases the light gathering power past a factor of 4. Effulgence of images also depends on how big an area the paradigm light is spread over. The smaller the surface area, the brighter the paradigm.

The magnifying ability of a telescope is the ratio of an object'due south athwart diameter to its naked eye bore. This depends on the focal length of both lenses.

Magnification = focal length of objective lens / focal length of eyepiece lens

Magnification might seem like the most important aspect of a telescope, only there are limits to how precipitous an paradigm a telescope can produce because of the blurring effects of the Globe's atmosphere. Magnifying a blurred image makes it bigger, only not clearer, so the priority when  telescopes are built is to have the greatest light-gathering power possible. Gathering more calorie-free makes brighter images, and brighter images brand information technology easier to see faint details.

Galileo is credited with being the beginning person to apply a telescope to make observations of the night sky. After hearing of the invention of the telescope in 1608, he built one of his own, called a Gallilean Telescope, in 1609 using a convex objective lens and a concave eyepiece lens. His telescope could magnify objects three times. Telescopes he made later magnified objects upwards to 30 times.

Limitations of Refracting Telescopes

Lenses create a blazon of image distortion known every bit chromatic aberration. This occurs considering as lite passes through a lens, different colors are aptitude through different angles (like in a prism) and brought to a focus at unlike points. Because of this, stars viewed through a simple lens are surrounded by rainbow colored halos. This can be corrected for by adding a thin lens of a unlike kind of glass behind the objective lens.

Lenses present other optical problems including how difficult and expensive it is to brand large lenses completely free of defects. Glass also absorbs virtually ultraviolet light, and visible light is substantially dimmed as it passes through a lens. In add-on, lenses in telescopes can only exist supported around the outside, so large lenses can sag and distort under their own weight. All of these problems impact paradigm quality and clarity.

An example to endeavour

A small refracting telescope has an objective of focal length 100 cm. If the eyepiece has a focal length of 4.0 cm, what is the magnification of the telescope?

Reply:

Magnification = 100/four.0 = 25 (usually written as 25×)

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Source: https://lco.global/spacebook/telescopes/refracting-telescopes/

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