Because mirrors are lighter, and they are easier than lenses to make perfectly smooth. To do that, the optics—be they mirrors or lenses—have to be really big. The bigger the mirrors or lenses, the more light the telescope can gather. Light is then concentrated by the shape of the optics. That light is what we see when we look into the telescope. The optics of a telescope must be almost perfect. That means the mirrors and lenses have to be just the right shape to concentrate the light.
If they do have such problems, the image gets warped or blurry and is difficult to see. A lens, just like in eyeglasses, bends light passing through it. In eyeglasses, this makes things less blurry.
In a telescope, it makes faraway things seem closer. A simple refracting telescope uses lenses to make images bigger and more visible. People with especially poor eyesight need thick lenses in their glasses. Big, thick lenses are more powerful. The same is true for telescopes.
If you want to see far away, you need a big powerful lens. Unfortunately, a big lens is very heavy. Heavy lenses are hard to make and difficult to hold in the right place. Prev NEXT. Physical Science. This is the simplest telescope design you could have. A big lens gathers the light and directs it to a focal point and a small lens brings the image to your eye.
The refractor telescope, which uses glass lenses. The reflector telescope, which uses mirrors instead of the lenses. The objective lens in refractors or primary mirror in reflectors collects lots of light from a distant object and brings that light, or image, to a point or focus.
An eyepiece lens takes the bright light from the focus of the objective lens or primary mirror and "spreads it out" magnifies it to take up a large portion of the retina. This is the same principle that a magnifying glass lens uses; it takes a small image on the paper and spreads it out over the retina of your eye so that it looks big. Cite This! Print Citation. Try Our Crossword Puzzle! If it enters at an angle, its speed and its direction will change.
The direction the light takes depends on whether it travels faster or slower in the new medium. Imagine driving a car from smooth pavement onto a sandy beach. If you approach the beach straight on, the car will slow down, but not change direction. If the you approach the beach at an angle, one of the tires will be slowed down by the sand before the other is, and the car will turn in the direction of the tire that touched the sand first.
Light follows the same 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 go faster. In the diagram below, light is leaving air and entering glass, so it bends towards the normal on the way in, and away on the way out of the glass.
Lenses form images by refraction and are typically made of either glass or plastic. They are ground so that their surfaces are either segments of spheres or planes. If a lens is convex or converging, it takes parallel light rays from a distant object and bends them so that they converge to a single point called the focal point.
The distance from the lens to the focal point is called the focal length of the lens. If a lens is concave or diverging, it takes parallel rays and bends them so that they spread out.
The rays will then appear to originate from a point in front of the lens. This point is also called the focal point, and its distance is measured in negative units.
The earliest telescopes, as well as many amateur telescopes today, use lenses to gather more light than the human eye could collect on its own. They focus the light and make distant objects appear brighter, clearer and magnified. This type of telescope is called a refracting telescope. Most refracting telescopes use two main lenses.
The largest lens is called the objective lens, and the smaller lens used for viewing is called the eyepiece lens. The size of an image produced by a lens is proportional to the focal length of the lens.
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