Most telescopes, and all large telescopes, work by using curved mirrors to gather and focus light from the night sky. The first telescopes focused light by using pieces of curved, clear glass, called lenses. So why do we use mirrors today? 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. Also, as they get thicker the glass stops more of the light passing through them.
Because the light is passing through the lens, the surface of the lens has to be extremely smooth. Any flaws in the lens will change the image. It would be like looking through a dirty window. Unlike a lens, a mirror can be very thin. A bigger mirror does not also have to be thicker.
The spy glass, or handheld refractor telescope, is one of the first optical telescopes. As Plotner explains, astronomers Galileo Galilei and Johannes Kepler improved this telescope's design at the turn of the 17th century, and today, amateur astronomers use refractor telescopes to study the skies--or spy on their neighbors across the street. Plotner states that even binoculars are a type of optical telescope. Photographers sometimes use optical telescope cameras with catadioptric lenses.
According to Astronomics. Some people even place optical telescope lenses on their iPhones so they can zoom in on targets to take close-up pictures. Many cameras with zoom are essentially optical telescopes, as the mechanisms behind many cameras' zoom lenses are the same as those behind the optical telescope--and both have the same job of magnifying distant objects. Researchers use sophisticated optical telescopes to study the universe in detail.
Many observatories house famous optical telescopes. Perhaps the most famous optical telescope is the Hubble Space Telescope, which STScI explains is a reflector telescope that has been orbiting Earth since taking photographs of distant astronomical objects.
Hubble's discoveries have significantly aided human understanding of the universe. Breakthroughs include understanding the age of the universe and a realization that the universe's expansion is accelerating. How to Use a Bushnell Reflector Telescope.
How to Use a Refracting Telescope. How to Use a Meade Telescope.
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