![]() ![]() A lens at one end of a tube, with the eyepiece and focuser at the other end, on a tripod mount of some kind.Ī refracting telescope works just like a magnifying glass. This (above) is what most people not famliliar with astronomy think of when you mention the word "telescope". ![]() Galileo could see objects 20 times smaller than the human eye could using his telescope. Galileo also used his refracting telescope to map mountains and craters on the surface of the moon, confirmed the phases of Venus, observed and analyzed sunspots, and misidentified the rings of Saturn as two bodies on either side of the planet which confusingly disappeared from time to time, as well as discovering that the Milky Way, thought at the time to be nebulous, was actually a multitude of stars packed so densly that they appeared to be clouds to the naked eye. He used it to discover the four largest of the moons orbiting Jupiter. Galileo Galilee made the first refracting telescope used to study space in 1609. He put the lenses into a tube to make the first refracting telescope. He found that a distant object appeared to be much closer when he looked at it through a concave lens and a convex lens held in front of each other. It is still close though, hence the name, "quasi-RC".A Dutch optician (someone who makes lenses for glasses), Hans Lippershey, designed the convex lens for the first refracting telescope in 1608. Because the mirror shapes have changed, the 2 mirrors alone no longer are a Ritchey-Chrétien telescope in the strict definition of the design. In the design of LCOGT's 1.0 meter telescopes, the shape of the mirrors has been changed a bit in order to find a more optimal optical design for the system as a whole. A true Ritchey-Chrétien has a hyperbolic primary and a hyperbolic secondary mirror. LCO's 1.0 meter telescopes are quasi- Ritchey-Chrétien telescopes. Schmidt-Cassegrain telescopes use a spherical mirror with a correcting plate that corrects the focus. Some telescopes use a combination of mirrors and lenses. Mirrors in modern telescopes area made in various shapes to correct for these errors. A spherical mirror surface is relatively easy to make, but different parts of a spherical mirror have slightly different focal lengths, so images will be fuzzy. However, images from a parabolic mirror will have a defect called coma, where images far from the center of the field of view are elongated. Parabolic mirrors will focus all incoming light rays to a single point. Also, unless the mirrors and other optics are kept at the same temperature as the outside air, there will be air currents inside the telescope that will cause images to be fuzzy.ĭifferent reflectors use different shapes of mirrors. Because they are normally open, the mirrors have to be cleaned. Reflecting telescopes have a few disadvantages as well. They are also easier to mount because the back of the mirror can be used to attach to the mount. Mirrors don't cause chromatic aberration and they are easier and cheaper to build large. Reflecting telescopes have many advantages over refracting telescopes. This arrangement is useful when optical equipment is being used that is too heavy to mount directly on the telescope. ![]() Coudé telescopes use a convex secondary mirror like a Cassegrain and an angled mirror like a Newtonian reflector to move the light rays to a focal point away from the telescope. Prime focus telescopes have no secondary optics and the observer or camera observes the image from near the focal point. Cassegrain reflectors have a convex secondary mirror and a hole in the middle of the primary mirror. There are several other types of reflectors that solve the issue of where to focus the light in different ways. One is called a Newtonian reflector, where a flat mirror is used to point the light rays out to an eyepiece. This focus is directly in the path of the incoming light, so there are several ways of making images from the mirror visible. If the surface is flat, the angle at which a beam of light approaches the mirror will be equal to the angle at which the beam is reflected, so i = r in the diagram below.Ĭurved mirrors can bend light and make parallel light rays converge to a focus. If the surface is smooth, like a mirror, the light will reflect in a predictable way. When light hits a surface that it can't travel through, it bounces back. ![]()
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