All telescopes function basically the same way: they collect light and focus it to a point. An eyepiece is then used to magnify the image at the focal point and present it to the eye of the observer. Some telescopes use a curved glass lens to
bend the light beams, causing them to converge at the focal point; others use curved mirrors.
The diameter of a telescope's main optical element (mirror or lens) is referred to as its aperture. Larger apertures collect more light, and therefore will produce brighter, sharper images. Aperture size is the most important
factor in determining a telescope's useful power.
There are 3 main types of telescopes used by amateur astronomers: Refractor, Reflector, and Mirror-Lens (Catadioptric).
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Long the most popular type of telescope, particularly for the beginning or casual observer, the refractor is what most people think of as a telescope: a long tube with a large lens at one end and an eyepiece at the other. The lens refracts or
bends the light to bring it to focus. Refractors produce high contrast images suitable for both land viewing and astronomical observation.
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The Reflector (sometimes called Newtonian Reflector) contains a curved mirror at the lower end of the optical tube. This bowl shaped mirror reflects light and gathers it to a point further up the tube, where, a flat mirror at an angle reflects
it into the eyepiece. Quality reflecting telescopes produce sharp, bright images of the entire range of astronomical subjects.
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Mirror-lens (catadioptric) telescopes use both mirrors and lenses together and represent the most advanced optical designs currently available for both the land viewer and astronomical observer. With their folded optics, mirror-lens telescopes
permit large apertures (yielding bright, highly resolved images) to be housed in relatively small, compact, and portable tube assemblies.
Aperture is the most important element of your telescope purchase as it determines what you see and the detail with which you see it. Measured in millimeters or inches, aperture is the diameter of the front end of the telescope where light is
collected. Because the primary purpose of a telescope is to collect light (not to magnify as commonly thought), a telescope that gathers more light performs better and can show greater detail of astronomical and terrestrial subjects. For example,
a 2" aperture telescope may show the cloud belts of Jupiter, but a 4" model will show added structure, color and smaller cloud belts not previously visible.
Focal length is a simple measure in millimeters of the path light takes before its focused in the eyepiece and is important to know when determining the magnification power. Focal ratio is the ratio of focal length to aperture. Long focal ratios
(e.g. f/16) yield narrower fields of view, but with higher-contrast images desired by planetary observers. Shorter focal ratios (e.g. f/4) yield extremely wide fields and faster photographic speeds, but generally with a lower level of image corrections
at the edge of the field. Most telescopes compromise at about f/10, a ratio that permits comfortably wide fields, reasonable photographic speed and very good image contrast.
The highest quality optical components result in telescopes that are rated as diffraction-limited. Simply, this means that the optical system's performance is of professional quality and is limited only by the principles of physics, with no additional
performance improvements technically possible.
Achromatic Meade refractor telescopes have a two-element lens design that greatly eliminates false color when light passes through the telescope. Apochromatic refractors also have a two-element lens design but also feature extra-low dispersion
glass, which entirely eliminates color problems and aberrations. The term apochromatic literally means "color-free." The result is a more accurate and sharper image than is possible with achromatic objective lenses.
Coatings are invisible coverings over a telescope's lenses and mirrors that work to improve the amount of light transmitted from the front lens to the eyepiece. Coatings are necessary because incoming light is lost as it passes through a telescope's
lenses and mirrors. High quality mirrors and lens greatly reduce the level of light loss, but telescopes need additional chemical coatings to reach a desirable level of visual clarity. Currently, Meade's standard mirror and lens coatings equal
or exceed the reflectivity and transmission of virtually any optical coatings offered in the industry.
UHTC, or "Ultra-High Transmission Coating," is a new technology developed by Meade to take coating precision even further. UHTC, like all coatings, works by reducing the amount of light lost in the focusing process, an inevitable
occurrence when light is passed through mirrors and lenses. Meade telescopes fitted with UHTC include an exotic and tightly controlled series of coatings on both sides of the correcting lens or plate. Multiple layers of aluminum oxide (Al2O3),
titanium dioxide (TiO2), and magnesium fluoride (MgF2) are applied to increase the per-surface light transmission of the correcting lens. In addition, primary and secondary mirrors are coated with aluminum enhanced with a complex stack of multi-layer
coatings of titanium dioxide (TiO2) and silicon dioxide (SiO2) for the ultimate in reflectivity. Averaged over the entire visible spectrum, total light transmission to the telescope focus increases by about 20% with the new UHTC coating.
Image brightness (i.e., the ability to see faint detail) of the 10" LX200GPS is, for example, effectively increased by about one full inch of aperture.
CCD (charge-coupled device) imaging is the capturing of digital images through a telescope. A special device called a CCD imager translates light from celestial subjects into a pixel display that can be immediately seen on a computer display,
can be stored on disc, used in digital image processing or printed for a hard copy display. CCD imaging offers a number of advantages over conventional astrophotography including instant image viewing, advanced image processing, greatly reduced
exposure times and improved image quality. All CCD imaging requires is a telescope with automatic tracking, a CCD imaging system and a personal computer (PC). In the simplest format, the CCD imager is placed into the telescope's eyepiece holder
in place of an eyepiece; the object to be imaged is center and focused; the image is taken and the data is transferred and processed by the PC. CCD imaging is best suited for Meade LX200 telescopes.
Due to the rotation of the earth, astronomical objects appear to move steadily across the night sky. When you use a telescope to magnify the view of an object, you also magnify the apparent speed of this motion.
A standard tripod mount will hold a telescope steady and might suffice for tracking celestial objects at low magnification. Objects move so rapidly through the telescopic field that the telescope must be mounted to facilitate
following celestial objects as they move across the sky.
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Smaller astronomical telescopes are often mounted on simple yoke-type mounts. In astronomical terminology these mounts are referred to as altazimuth mounts, derived from "altitude" (vertical) and "azimuth" (horizontal). Altazimuth mounts permit
vertical and horizontal motions of the telescope. By combining vertical and horizontal motion, the observer can follow celestial objects in their paths across the sky.
Astronomical objects do not move vertically or horizontally, however, but rather at an angle dependent on the observer's latitude. Tracking these objects through an altazimuth-mounted telescope therefore requires moving
the telescope simultaneously on the two telescope axes. This procedure is satisfactory for astronomical observing with telescopes to about 60mm (2.4") aperture.
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The equatorial mount allows easier tracking of celestial objects by aligning one telescope axis with the Earth's polar (rotational) axis. In this way, tracking of astronomical sights can be achieved by using one knob to move the telescope along
a single axis, instead of the two simultaneous motions required of the altazimuth mount. The Earth's rotational axis points nearly to Polaris, the North Star. Alignment of an equatorial mount to the Earth's polar axis is therefore approximately
equivalent to pointing one axis to the North Star. This simple operation (requiring perhaps 2 minutes time) must be performed before each observing session with an equatorially mounted telescope.
Equatorially mounted telescopes usually include tow dials, called setting circles, with one dial attached to each telescope axis. Setting circles permit the location of faint celestial objects directly from their catalogued
celestial coordinates. Another advantage of the equatorial mount is that a small electric motor may be connected to the telescope's polar axis, for fully automatic tracking of astronomical objects. Alternatively, altazimuth mounted telescopes
with the Meade Autostar Computer Control System circumvent the need for a true equatorial mount as the Autostar moves and tracks objects on both axis simultaneously. Otherwise, equatorial mounting generally requires purchase of an Equatorial
Wedge or a specialized tripod.
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Dobsonian mounts come exclusively on reflector telescopes and are extremely simple, which helps reduce the overall cost of the telescope. The mount sits on the ground and two pads on the telescope sit in the cut-outs of the mount. When set-up,
the telescope moves up, down, left and right with ease, while providing solid stability. Dobsonian mounts are priced well below other mount types, freeing up your budget to spend on more accessories or a larger aperture.
The magnifying power of a telescope can be varied by changing the eyepiece. Like telescopes, every eyepiece has a focal length usually marked on the top or the side. They range from 55mm (low power) to 4mm (high power). To determine the magnification
given by any particular combination of telescope and eyepiece, divide the focal length of the telescope by the focal length of the eyepiece (using the same units of measurement for both).
The maximum magnification that a telescope can produce while keeping a clear, bright image is 2 times the aperture in millimeters (or 50 times the aperture in inches.) For example, the maximum usable power for a 60mm telescope
is 120x.
Magnification of a telescope is determined by dividing the focal length of the main or objective lens by the focal length of the eyepiece. A 1000mm objective used with a 25mm eyepiece will produce forty power (40X) of magnification.
No. In fact, the magnifying power of a telescope is an essentially meaningless specification. Remember that the magnifying power of a telescope is determined by its eyepiece, which simply enlarges the image formed by the telescopes main optics
(lens, mirror, etc.) to a size convenient for observation with the eye. With a high power eyepiece any telescope can magnify hundreds of times. Over-magnifying, however, will result in an image that, while larger, is also dimmer and more blurry.
The important factor is the telescope's aperture - the size of its main optics. This is what determines the amount of light that a telescope collects, and as a result the level of detail and resolution which the instrument
can achieve. The larger a telescope's aperture, the more detail will be visible.
Atmospheric conditions also play a part in limiting a telescope's useful magnification power. The Earth's atmosphere can sometimes cause a distortion of the telescope's view. At low power, the effect may be unnoticeable. But
at high power, it can result in a badly blurred image.
The most common mistake of the beginning observer is to "overpower" the telescope and to use magnifications which the telescope's aperture and typical atmospheric conditions cannot reasonably support. The result is an image
which is fuzzy, ill-defined, and poorly resolved, through no fault of the telescope. Keep in mind that a smaller, lower-power, but brighter and well-resolved image is far superior to a large, high-power, but dim and poorly resolved one.
The best advice when viewing any object is always start out at the lowest power and, by exchanging eyepieces, gradually build up to higher magnifications until the object is best seen.
All lenses produce images that are upside down. To flip the telescope image around requires certain lenses or prisms which absorb and scatter the light the telescope has collected. An erecting prism between the scope and the eyepiece can be used
to rotate the image. This is especially useful when one wishes to use the telescope for terrestrial viewing.
There are plenty of optional accessories and equipment which can be acquired to enhance the power and utility of your telescope. We offer an array of accessories to better enhance viewing including filters, barlow lenses, plossls, astrophotography
accessories, camera adapters and erecting prisms.
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Color filters are an essential tool of the lunar and planetary observer. Filters permit the observation and photography of surface detail that is often virtually invisible without filtration. Depending on atmospheric conditions on both the Earth
and the planet being observed, the advantages of color filters can be anywhere from subtle to dramatic. Color filters allow a range of contrast enhancements that are very useful for bringing out details of structure and pattern in the planets.
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Prisms and mirrors help you improve your viewing situation for both astronomical and terrestrial applications. Erecting prisms are most helpful for terrestrial viewing as they correct images with reversed left/right orientation and provide a
comfortable 45° viewing position. Likewise, diagonal mirrors provide a comfortable viewing position and can allow for larger eyepiece diameters.
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Barlow Lenses increase the effect of eyepieces. Barlow Lens are "negative" lenses that increase the effective focal length of a telescope and double or triple the power of any eyepiece. For example, combined with a 2X Barlow, a 20mm eyepiece
becomes a 10mm one. A high quality Barlow lens can effectively double the size of your eyepiece collection.
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Every amateur astronomer should take the time to learn how to adjust and read a planisphere and star map. A planishpere shows which constellations are visible at a particular time and date, while a star map shows details for star clusters, galaxies,
and nebulae. Observing without a star map can prove to be very frustrating to any observer, as they point their telescopes aimlessly at the sky.
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Simple adapters available for most telescopes along with a T-mount for your 35mm camera brand allow the coupling of 35mm camera bodies to the telescope. The telescope thus becomes the camera lens, opening up the dramatic worlds of long-focus
astrophotography. With a motor-driven, equatorially mounted telescope, high-quality photographs of the Moon and planets are relatively straightforward; long exposure photographs of deep-space objects require special "guiding" accessories which
permit the observer to monitor the exposure continually and to assure that the telescope remains precisely pointed at the object during the exposure.
Coma is an optical phenomenon that results when off-axis light rays are reflected by a parabolic mirror and brought to a focus. The effect is star images away from the telescopic center of the field of view are not round, but have a somewhat
triangular shape. Coma generally becomes apparent at focal ratios below f/6, with the effects increasingly pronounced at focal ratios of f/4. Meade Schmidt-Newtonian reflectors are designed to reduce the effects of coma by one-half, thereby allowing
the benefits of wide-field viewing and fast photographic speeds with very little coma visible. |
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