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SkyQuest™ XT8 8"(20cm) DobsonianThis model was discontinued in August 2003 when it was replaced by the new SkyQuestª XT8 Intelliscope™. But then due to popular demand for a more fundamental option, it was reintroduced as the Classic XT series in January 2004.The first Orion product Company Seven chose to place on line! The Orion SkyQuest™ Dobsonian telescopes are designed for beginners who seek the best possible view of the faint Deep Sky objects while on a constrained budget. These telescope benefit from years of study and refinement of those Dobsonian style telescopes already on the market; they include advanced design and materials to keep them lightweight and simple to use. Furthermore, the accessories included are common sense items to insure a good first night out; these are items that would normally be optional for competing telescopes. While the original Orion SkyQuest™ XT8 telescope became the most highly recommended production 8" Dobsonian style telescope, and was the reference standard for its type at Company Seven, Orion simply couldn’t leave well-enough alone. Orion took the Dob that earned “best of the batch” honors from Sky & Telescope magazine (1/00) and enhanced it with even better engineered features, and accessories! And then Orion dropped the price, to boot. Our popular Orion SkyQuest XT8 telescope now provides you even more bang for the buck. Great light-gathering power, point-and-view simplicity, great optics, a rock-stable mount, and a host of features not found on competing Dobs. For any astronomer seeking serious adventure, the XT8 has it all!
Above Right: The Orion XT8 8"f6 Dobsonian telescope, current October 2001 model shown (17,527 bytes). This telescope provides 48 inch focal length (f6 focal ratio), a versatile choice for amateur astronomy. This is part of the equation that provides good portability while retaining a good range if useful magnifications. The 8" aperture model is our most popular "first telescope" Dobsonian reflector, particularly attractive among those who desire an easily manageable telescope with the light gathering and fields of view potential to recognize many of the most popular deep sky objects (Galaxies, Star Clusters, Nebulae, Planetary Nebulae, etc.). And yet this telescope affords the good contrast and clarity qualities required for lunar and planetary observing which actually may show changes through out an observing season. With a comparatively small central obstruction, and fewer optical surfaces, the contrast and brightness can actually surpass more expensive and complicated designs such as the 8" Schmidt-Cassegrain telescope. What characterizes a reflecting telescope?: The Optical Tube Assembly (OTA) is an arrangement of the classic Newtonian reflecting telescope. An English mathematician originated this optical design although Sir Isaac Newton first made it. This system employs two mirrors. The Parabolic "Primary" mirror (illustrated below, and as seen from behind the telescope optical tube at left) is the factor by which most telescopes are described; hence an 8" telescope has a primary mirror of 8 inch (203mm) in diameter with a versatile 1200mm mm focal length (f5.9). The Primary mirror of the telescope is precisely mounted in a Cell at the rear of the telescope. The light entering the telescope is gathered and then reflects forward in a converging beam, to the elliptical Secondary Mirror that is positioned near the front of the telescope. This Secondary Mirror is supported in a tilted position so that to the light path the obstruction appears circular. The Secondary Mirror diverts the light from the Primary Mirror to the side and beyond the Focuser. The Secondary Mirror is attached to an adjustable Mirror Cell, and this assembly is held in place by a new (improved Oct. 2001) four vane Spider; this assembly is shown above and to the left as seen from the front of the telescope. The light from the Primary mirror is then reflected out to the side of the telescope achieving focus at a point beyond the focuser. An eyepiece for viewing, or camera for photography is placed at the focuser.
Among the considerations of a reflecting telescope is that the mirrors be precisely positioned within the OTA in terms of centering, tilt, and spacing. The overall alignment ("collimation") of the one optical element to the other, and their placing the focal plane (the point where the image comes to focus) at the correct position beyond the focuser are critical. The optical axis of the telescope should be closely parallel to the mechanical axis of the tube assembly too. Company Seven chose Orion's SkyQuest™ telescopes in part because of their consistently well engineered, good quality mechanical components, and partial assembly at the factory that facilitate collimating these telescopes precisely upon delivery, if needed.
A well made reflecting telescope can offer the best view per the dollar of the faint, deep sky objects where light gathering power is essential. Light gathering power increases are more important and come quicker than one may think; consider that a 6"f8 reflecting telescope may show objects about 335X fainter than the unaided eye, while an 8"f6 may offer 600 to 650X the light gathering power over the unaided human eye - in astronomy size can matter! The Dobsonian telescope: The characteristic simple to use Alt-Azimuth mounting, use of a lightweight primary mirror and modestly priced components evolved in the 1970's with San Francisco sidewalk astronomer John Dobson. His goal was to get the most telescope possible into the hands of the amateur observer for the lowest relative cost. This arrangement has become known as the "Dobsonian" or "Dob". The Dobsonian telescope consists of an optical tube assembly riding on a wooden alt-azimuth platform. The optical tube may be made of tube up to 18 or 20" in diameter. These tubes are typically made of Sonotube/cardboard, or plastic, or rolled metal. The Orion XT telescopes employ a rolled metal enameled tube finished internally in an anti reflection paint. This tube holds optical collimation well even with temperature or humidity changes. This thin wall tube permits the designer to select a smaller secondary mirror/obstruction. And this keeps the tube lighter weight and more compact than heavier Sonotube tubes. In the case of the better made larger Dobson telescopes (12-1/2 inch and larger), a Truss arrangement is employed in order to facilitate disassembly into a more manageable and compact package. Our best-made Dobson telescopes up to 10 inch aperture are those offered by Orion. While our larger Dobson telescopes include the Truss tube telescopes made by Astro-Systems. Working with Gravity: The center of gravity lies directly over the center of rotation in both directions, so no matter to where the telescope is pointed, the weight is evenly distributed through the mount to the ground. This characteristic, and sound design results in almost complete elimination of unwanted vibration and oscillation; the inevitable downfall of many poor telescope mounts. Whereas in many economical telescopes the image seems to bounce around forever after the scope has been touched, this is not the case with well made Dobsonians. A Hands-On Telescope: The Dobsonian is a telescope you can push around - literally. You point it by simply nudging the tube on its Base up or down, and left or right by hand. Trunnions on the tube rotate on low-friction plastic bearings, allowing the telescope optical tube assembly to move up and down (altitude). The Base rotates horizontally (azimuth) around a center pivot permitting the observer to move the telescope smoothly up and down, left and right on Teflon/Nylon altitude and azimuth bearings. A gentle nudge is all it takes to point the scope right where you want it. The motion on both axes is "buttery smooth," letting you guide the scope with just the lightest touch from one part of the sky to another. Exploring the heavens is relaxing and fun for everyone, the way itÕs meant to be. The XT8, like all SkyQuest Dobs, features the innovative Correct-Tension Friction Optimization system. It provides just the right amount of friction on the altitude bearings to ensure smooth motion and perfect tube balance. You donÕt have to rebalance the scope every time you change eyepieces or add a barlow lens or other accessories. No need for fishing sinkers, stacks of washers, or other clumsy counterweights as required with other Dobs! The CorrecTension springs also hold the optical tube captive on the base.
You do not need to loosen and tighten clamps when targeting objects, as you must with other mounts. Dobsonians are not equatorially mounted and so they are generally moved only by hand. While it is possible to add motors and computer control (to automatically find and track stars) it is generally not necessary or cost effective on smaller Dobsonians. Some companies do sell Dobs complete with tracking systems however, even these factory made tracking Dobsonians are not completely satisfactory for deep-sky astrophotography. Nor do Dobsonian telescopes have setting circles for locating objects by their cataloged coordinates. Company Seven does offer optional electronic Encoder and digital display devices as aids to celestial navigation. Many people find the beauty of a Dob is in their no-frills simplicity - they just work. The Dobson design remains the first choice among serious deep sky observers, and it is not uncommon to find custom or home made 8" to 36" aperture "Dobs" in use at dark sky observing sites around the world. The Orion SkyQuest™ Dobsonian telescopes sold by Company Seven in the 6" to 10" apertures provide excellent affordability and simplicity of operation, this makes these Dobsonians a great first telescope for entry into the hobby of amateur astronomy. Larger Dobs, though bulkier to transport and often requiring a step stool or ladder to reach the eyepiece, remain highly popular among experienced observers. Compared to similar-aperture Newtonians on their heavy equatorial mounts (and at times awkward eyepiece position), Dobsonians are delightfully economical. Experienced amateurs often claim that the best combination of portable telescopes for most persons pursuing astronomy would be an 18" to 20" Dobson, with a 6" Apochromatic Refractor!
Noteworthy features of the SkyQuest™ XT8 include:
"Starry Night Special Edition" is a basic version of the more capable "Starry Night" version 5.0 astronomy software series; this software will help you learn the night sky, see what is up day or night, now or in past millennia, plan your observing sessions, and print out charts and information about the celestial wonders. The set also includes "SkyTheatre", a DVD by Imaginova so your television or PC becomes a spaceship on a voyage through our Solar System. The set is compatible with both Macintosh computers running OSX version 10.3 or later, and with Windows XP for PC. Your personal planetarium and guide to the night sky!
Left: CD-ROM "Starry Night Special Edition" with bonus "SkyTheatre" DVD suite (43,322 bytes). XT8 8"f6 Telescope Specifications:
* Specifications are subject to change without notice.
To read additional information about the Orion SkyQuest™ XT8 telescopes Note: this download size is 426,043 bytes (in Acrobat Reader ".pdf" format).
COMPANY SEVEN'S ASSEMBLY & TESTING SERVICE:All of the information we provide on line and by phone or E-Mail to the customer, our expertise, our unrivaled showroom and museum (an increasing rare sight), and the fact that one may buy the basic instrument from us or elsewhere at about the same cost should be enough to persuade one to choose Company Seven. However, we do even better, we make it in your interest to buy from us.Orion has been quite good at making the factories overseas produce a great value. But once in a while something less than perfect slips by; a part is not glued just right, something is installed a bit off, or a component is damaged in transit. If you receive one of these telescopes and if you know enough to recognize an anomaly then it is a simple matter to call Orion or Company Seven for a prompt exchange or replacement parts. We both have very good reputations for after sale support and a money back guarantee.
When we assemble the XT we evaluate cosmetics, often cleaning off surplus glue or dirt. We install the Primary Mirror making those first and most time consuming adjustments to assure each optical and mechanical component is nominally installed. We are happy to provide you with the optional tools to collimate a telescope when it becomes necessary (after all some years from now you will probably want to pull the mirror for cleaning) and more importantly we will teach you how best to proceed. As we have worked on so many of these instruments we have developed a good sense of how a properly made and adjusted Focuser should feel. We know the tricks to make the telescope move smoother up and down, left and right. We know how to make it last longer - in fact we change out some components with superior alternatives. We find the quality control problems however, while we do not expect a "Rolls Royce" fit and finish on the XT telescopes, we work so that the telescope will perform as well as experience shows it can. And as we process the telescope we perform some tests that will reveal to our experienced eye whether or not the optics were made and collimated as they could be. And finally, we generate additional information that is provided to the owner; this will characterize the potential of the telescope for visual applications, and with an optional Equatorial Mount what the XT may accomplish photographically. One will never read a sad tale from someone who actually bought their XT at Company Seven. We invite you to attend a Star Watch activity of any regional astronomy club and compare a telescope that bears the Company Seven acceptance label with those from elsewhere. In fact more and more we hear accounts of people at such events who bought their "Orion XT clone" elsewhere being convinced it was a great value until they felt the motion of our telescopes and gazed through the eyepieces we recommended. Company Seven's customers tend to progress further in the hobby than others. This is in part because we are helping them as we wish someone else would have helped us. We are not archetypical salesmen, instead we are experts who can teach you about the instruments and provide the sincere good counsel.
SUGGESTED ACCESSORIESThese are optional accessories that are not included with the telescopes that we highly recommend for your viewing pleasure and long term success:
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Left: Parabolic Primary Mirror of an Orion Dobson telescope in it's Cell (12,056 bytes).
Left: The Trunnion arrangement of an Orion Dobsonian telescope. Note convenient lever with handle to move telescope up and down (11,022 bytes).
