SkyQuest™ XT6 6" (15cm) f8 Dobsonian

Improvements included since October 2001 described here

Right: Shown is a SkyQuest™ 6" (15cm) telescope. Notice the 1.25" Rack & Pinion Focuser, Accessory Tray, Trunnion with Handle. (13,850 bytes).

This is the least expensive reflecting telescope suggested by Company Seven for astronomy. It offers a chance to get one into the hobby, and retain their interest for some time. The XT-6 is a telescope that many children or older adults can manage. This is the best choice of telescope which we offer for children from about 8 years of age to 14, although the larger Orion 8" XT8 should be considered for serious teens or adults. This is as easy as it gets, and is a very good value first telescope package - the least costly "first" telescope really worth owning for many!

The 6" aperture reflector has traditionally been suggested by fellow astronomers as the first serious telescope for the amateur up through the 1970's. It had the minimum light gathering power needed to recognize deep sky objects and the major planets. However, since the growing urban sprawl has so light polluted the skies, it has made the 6" (as most telescopes) less effective for deep sky objects in suburban settings.

In his best-selling book Nightwatch: A Practical Guide to Viewing the Universe, veteran author and astronomer Terrence Dickinson says, "There may not be a perfect telescope for the beginner, but the closest thing to it is the 6-inch Dobsonian-mounted Newtonian reflector."

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 (rolled metal enamel finished tube for example) 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.

The 48 inch focal length f8 focal ratio of the XT6 (and the larger XT-8) telescopes afford versatility and a range if useful magnifications, while retaining good portability - the XT-6 will fit into almost every car. The XT6 is particularly attractive to those who can not, or do not wish to manage a larger telescope yet seek a manageable telescope with the light gathering and fields of view potential to recognize many of the most popular deep sky objects (depending on your skies) including a few Galaxies, many Star Clusters, Nebulae, and some Planetary Nebulae. And this telescope affords the good contrast and clarity qualities required for lunar and planetary observing which actually may show changes over the course of an observing season - or see a transit of a moon passing across the surface of Jupiter! With a comparatively small central obstruction and fewer optical surfaces, the detail seen and brightness can actually surpass more expensive designs such as the 3.5" (90mm) and 5" (125mm) Maksutov-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 is the factor by which most telescopes are described; hence an 6" telescope has a primary mirror of 6 inch (15cm) in diameter.

The light entering the telescope is gathered at the Primary Mirror and then reflected 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.

Left: Parabolic Primary Mirror of an Orion Dobson telescope in it's Cell (12,056 bytes).

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.

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 good quality mechanical components and 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 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. 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. 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.

Left: The Trunnion arrangement of an Orion Dobsonian telescope. Note convenient lever with handle to move telescope up and down (11,022 bytes).

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™ XT6 include:

• A set of accessories of good quality are provided to get you up and running the first night out!
  • Orion 25mm Plossl Eyepiece (49X providing 0.92 Degree Field of View)
  • Orion 9mm Plossl Eyepiece (136X providing 0.36 Degree Field of View)
  • Orion 6x30mm Finderscope with Mounting Bracket
  • Moon Filter (to attenuate brightness of Moon, planets)
  • Eyepiece Holder
  • Plastic snap-on OTA Cover

• Adjustable Friction, Altitude Bearings
• Low-mass molded molded expertly finished Primary Mirror made of "Ultraplex", a type of plate glass marketed for optical use
• Primary and secondary mirrors are aluminized and over coated with a transparent Silicon Monoxide protective coating assuring good longevity
• Unique adjustable Mirror Cell to support the Primary Mirror
• Durable aluminized mirror coatings
• Optics hand finished and tested on a 125 line Ronchi
• Silky smooth cast and machined aluminum 1.25" diameter Rack & Pinion Focuser
• Focuser Lock
• Convenient "Navigation Knob/Grip" on the optical tube.
• Convenient grip/carrying handle on the Base.

Receive a FREE Where the Stars Are™ Astronomy CD-ROM with purchase of any Orion-brand astronomical telescope. It's your personal planetarium and guide to the night sky. An $89 value!

Left: Orion's CD-ROM "Where The Stars Are" (12,872 bytes). Click on image at left to view enlargement

  XT6 Telescope Specifications:

Maximum Height Overall: Maximum Height to The Eyepiece: Length of Optical Tube Assembly: O.A. Diameter of Optical Tube Front Cell: Weight of Optical Tube Assembly: Weight of Carriage: Effective Light Gathering Power:

50 inches (with lens cover) 45 inches 45 inches (with lens cover) 7.2 inches (182.6mm) 13 lbs. 24 lbs. About 350X that of Human Eye

* Specifications are subject to change without notice.

For additional information about the Orion SkyQuest™ XT6 telescopes sold by Company Seven download the Orion illustrated instruction manual from Company Seven's Library. Download size is 426,043 bytes (in Acrobat Reader ".pdf" format).

SUGGESTED ACCESSORIES

1. Guide book: "Backyard Astronomers Guide" or "Nightwatch" by Terrence Dickinson, or "Starware" by Phil Harrington. For the novice from age 8 to 15 or so up to adult. Good introductions to astronomy, the use of telescopes, and their accessories. Easy introductions to finding ones way around the night sky.

2. Telrad illuminated sight: to aid one in finding and centering objects in the main telescope, and learn the sky by "star hopping" from one object to another

3. Planisphere: the easiest way to find what is up in the sky at any given time and date, and an aid to planning future sessions.
   

4. Red LED Flashlight such as the Rigel Skylite to help one set up and use a telescope, and to read charts or a planishpere without adversely impacting the observers night vision.

5. Orion Collimating Eyepiece or AstroSystems Collimating tool set, each with instructions.
   

6. Neutral Density and Color Filters to reduce the brightness of the Moon and Planets, and highlight subtle features.
   

7. Sky Light Pollution Rejection Filter to reduce the greenish or golden background glow from city lights and darken the sky background - aid seeing faint Nebulae.

   

8. Orion fitted Carrying Bag for safer, and more convenient transport the telescope optical tube assembly. Keep in mind that these are very convenient and lightweight bags, but are not suitable for shipping a telescope.
   

9. Eyepieces: Orion includes two eyepiece with this telescope, 9mm and 25mm Plossls. Typically astronomers will wish to initially set up the telescope with at least two or three 1.25" eyepieces to address:
   
   • Low magnification: for views of the faint deep sky objects a 32mm to 40mm focal length eyepiece.
     

   • Middle Magnification eyepiece - usually between 80 to 120X, for views of the full Moon, Star Clusters, etc.
     

   • High magnification: 200X or more for views of the planets
     

   Eyepiece designs such as the Plossl, Orthoscopic are acceptable. If you object to less than perfect images particularly at the edge of the field, and if you require long eye relief (distance from lens to the eye) to accommodate spectacles, then Company Seven recommends eyepieces of advanced designs such as those pioneered by Al Nagler, founder of the TeleVue company. TeleVue's advanced designs include the "Nagler", "Radian", or "Panoptic" series eyepieces. These oculars will provide the widest clear, and flat field images bringing out the most in your telescope (and many other) telescopes. Wider field of views are also desirable since as the Earth rotates and objects drift across the field of view, a wide angler ocular shows an object for some time longer before having to adjust the telescope.
   

   Please refer to the brochure and the test report/data from Company Seven enclosed with our telescopes for detailed characterizations of suggested eyepieces:

   Eyepiece	Magnification	Actual field of view	Exit pupil
   40mm Plossl	31x	1.27 degrees	5.0mm
   32mm Plossl	38x	1.26 degrees	4.0mm
   25 Plossl (included)	49x	0.92 degrees	3.1mm
   22mm Panoptic	55x	1.17 degrees	2.75mm
   19mm Panoptic	64x	1.00 degrees	2.37mm
   15mm Plossl	81x	0.59 degrees	1.9mm
   12mm Radian	102x	0.59 degrees	1.50mm
   9mm Nagler	136x	0.58 degrees	1.12mm
   9mm Plossl (included)	136X	0.36 degrees	1.12 mm
   6mm Radian	203x	0.30 degrees	0.75mm

10. Barlow or TeleVue "Powermate" Lens: Company Seven suggests you consider any of a number of 1.25 inch diameter Barlow lenses that we offer to double your magnification. You may find it helpful to contact Company Seven for suggestions on how to to best meet your goals.

11. Equatorial Mount: being constructed of an aluminum tube, some time in the future you could buy a good quality used equatorial mount and improve the usability of this telescope to better attain its high magnification potential. A telescope of this length and torque requires a good quality, rigid platform to support it. We recommend you consider:
    
    • Vixen Great Polaris DX mount.
    • Losmandy Hollywood General Machining Model GM-8 mount.