The most important characteristic of a telescope is its aperture - the diameter of its light-gathering lens or mirror, often called the objective. Aperture: A Telescope's Most Important Feature But don't overlook portability and convenience - the best scope for you is the one you'll actually use. And all other things being equal, big scopes show more and are easier to use than small ones, as we'll see below. The telescope you want has two essentials: high-quality optics and a steady, smoothly working mount. Armed with these few basic types of telescopes, you'll have a good idea what to look for (and what to avoid) when scouring the marketplace for your new scope. So here is a guide to help you make sense of the "universe" of telescope models available today. Many (arguably most) good starter scopes cost $400 or more, though some superb choices are available for under $250. Instead, you should choose a telescope based on your observing interests, lifestyle, and budget. It can be a portal to the universe and provide a lifetime of enjoyment.īut there's no one "perfect" telescope - just as there's no such thing as a perfect car. It is still close though, hence the name, "quasi-RC".With a little guidance, you can pick a high-quality telescope that can last a lifetime.Ī telescope is a popular gift, especially so during the holidays. 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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