8" f/6 telescoping truss-tube Dobsonian

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This Sky-Watcher Dobsonian has:

• fully multicoated 8” f/6 Newtonian reflector optics
• unique telescoping truss-tube design for compact transportability
• smooth Teflon bearings, plus altitude tension control
• 10mm (120x) and 25mm (48x) 1.25” Plössl eyepieces
• 8 x 50mm right angle finderscope

    With the 8” Sky-Watcher telescoping truss-tube Dobsonian, you don’t have to worry about lifting the scope’s diagonal mirror cage and trying to bolt it to three swaying truss tube in the dark as you do with other truss-tube Dobs. Sky-Watcher's revolutionary telescoping truss-tube system attaches the top of the truss tubes permanently to the diagonal mirror cage, with the bottom of the tubes sliding into three die-cast housings on the scope’s primary mirror tub. This unique system allows the optical tube's diagonal mirror cage and three attached truss tubes to slide down onto the primary mirror tub to form one compact 32.5” long assembly. The cage and tub can then be locked together, using no-tool handles built into the primary mirror tub, and lifted out of the scope’s altazimuth rocker base for easy and secure telescope transport.

    Assembling the Sky-Watcher Dob for use involves simply unlocking the diagonal mirror cage and raising the cage until spring-loaded catches on the truss tubes snap into place in the primary mirror tub. This holds the cage at its fully-raised position while you tighten the no-tool handles at the base of the truss tubes to lock the diagonal mirror cage securely in position for observing.

    For binoviewing without unwanted extra magnification, a second set of indents on the truss tubes allows the diagonal mirror cage to be lowered to a preset locking position on the truss poles. This lets you to use a binoviewer without needing a corrector or Barlow lens in the binoviewer to reach focus.

    The complete Sky-Watcher telescoping truss optical tube assembly – diagonal mirror cage, integral truss tubes, and primary mirror tub – weighs only 24.2 pounds (11 kg). The altazimuth rocker box base it sits in weighs only 26 pounds (11.8 kg). Total weight is a light 50.2 pounds. When aimed at the zenith, the eyepiece is 45.5" above ground level.

    The Sky-Watcher easily collapses in minutes into two small and light components that fit into a car trunk or into the back seat of a compact car. Competitive truss-tube Dobs break down into four or more components – diagonal mirror cage, primary mirror tub, altazimuth rocker box base, and truss tubes (as many as six to be carried separately or packed into an optional carrying bag). It’s easy to see how the two-part Sky-Watcher has a definite convenience advantage over the four or more parts of a conventional truss-tube Dob. And, unlike bulky competitive solid-tube Sonotube or metal tube Dobs with an unwieldy 48” or 50” long optical tube, you don’t need a big car to transport this 8” Sky-Watcher.

    Assembly and disassembly take only about 5-10 minutes, with no tools needed. After you set up, particularly after traveling over bumpy roads to a dark sky site, take a few moments to check the collimation of the optics to assure peak performance and you are ready for an evening of fascinating viewing at your favorite dark sky location. The 8” Sky-Watcher telescoping truss-tube Dobsonian is designed for visual observing only – to show you as much of the night skies as possible, and do it as conveniently and inexpensively as possible. Photography is not possible with a Dob.

    Because of its compact component size, light individual component weights, and limited number of components to put together (after all, there are only two!), the 8” Sky-Watcher telescoping truss-tube Dob can be transported and set up easily by one individual. This innovation gives Sky-Watcher users a cost-effective 8” telescope with unsurpassed compactness and transportability.

This Sky-Watcher Dob’s Optical Tube Assembly . . .

  • Newtonian reflector optics: 8” diameter parabolic primary mirror, with 1.85” m.a. diagonal mirror. Both are guaranteed to be diffraction-limited. The diagonal mirror cage and primary mirror tub are made of rolled aluminum, anodized and finished externally with a subtle and attractive star-field pattern. Painted die-cast and machined rims hold the aluminum truss tubes and optical components in precise alignment to minimize the need for frequent collimation.

  • Primary mirror: Grade A annealed optical glass, 8” diameter, 1200mm focal length, f/6 parabolic in a fully adjustable metal cell provides sharp and bright high contrast images of nebulas, galaxies, and star clusters. The well-balanced f/6 focal ratio shows you subtle lunar and planetary details inside the solar system, as well. The center-spotted mirror is ground with computer-controlled accuracy, multicoated with aluminum and titanium dioxide for high reflectivity, and then overcoated with quartz for long life.

  • Diagonal mirror: Grade A annealed optical glass 1.77” m.a. diagonal mirror, mounted in a fully adjustable diagonal holder on a low-diffraction four-vane thin spring steel spider. The diagonal mirror is polished flat to diffraction-limited accuracy. As with the primary mirror, the diagonal is multicoated with aluminum and titanium dioxide for high reflectivity and overcoated with quartz for long life.

  • Finderscope: 8 x 50mm right-angle erect image achromatic crosshair design. The images in the finder are erect and right-reading, with star patterns looking just as you see them on star charts or with your bare eye. It is mounted near the focuser, with the finder eyepiece vertically aligned in the same direction as the telescope eyepiece. This eliminates the constant head twisting involved when switching between the horizontal orientation of a conventional Dob’s straight-through or red-dot finder and the vertical orientation of its focuser and eyepiece.
  • Focuser: machined aluminum single-speed 2” Crayford focuser with a 1.25” eyepiece adapter.
  • Eyepieces: 10mm and 25mm 1.25” four-element Plössl eyepieces with a 52° apparent field. The 25mm provides a magnification of 48x with an actual field of view that is 1.08° across. That’s more than twice as wide as the full Moon. The 25mm gives rich and expansive deep space views of star clouds, galaxies, and nebulas alike. The 10mm Plössl provides a stout 120x magnification with a 0.43° field of view, enough magnification to provide sharp close-up views of the Moon, planets, globular star clusters, and more.
  • Optical tube dimensions: Tube diameter (outside of one side bearing to the outside of the other bearing): 11.25"; tube length collapsed: 33"; tube length extended: 44".

This Sky-Watcher Dob’s Base Assembly . . .

  • Rocker box altazimuth base: The altazimuth rocker box that the mirror tub rides in is crafted of strong, lightweight, and water-resistant laminated particle board, as is the water-resistant ground board that the rocker box rides on. The base is shipped disassembled, but can be put together in about a half an hour using only a screwdriver and the supplied hardware. Teflon bearings in both altitude and azimuth provide smooth and effortless motion of the optical tube in all directions. At the same time, the Teflon provides the proper amount of stiction to assure backlash-free movement, without the inadvertent and uncontrolled motions sometimes caused by wind gusts pushing on mounts using azimuth roller-bearings.

  • Navigation knobs: Two navigation knobs conveniently mounted on the diagonal mirror cage makes it easy to control the scope’ motion in any direction. The optical tube starts moving at a gentle touch – smoothly and with no fuss. Center on an object and the scope settles down immediately, with no shudder or vibration to mar your viewing experience. The knobs also act as an aid in installing the optical tube into the base.

  • Carry handles/altitude tension control/eyepiece tray: The handles in the sides of the rocker box incorporate a tension control in altitude that lets you compensate for eyepieces of markedly differing weights. An eyepiece tray capable of holding one 2” and three 1.25” eyepieces attaches to the front of the rocker box above the supplied centrally-mounted carrying handle.
  • Altazimuth base dimensions: 20" in diameter by 29" high.

What can you see through the 8” Sky-Watcher telescoping truss-tube Dob?

    Outside the solar system, the night sky is filled with fascinating objects within the reach of the 8” Sky-Watcher Dob. In the constellation Sagittarius lie several of the sky's most prominent emission nebulas. The Lagoon Nebula (M8) is a rich aggregation of dust and gasses illuminated by its youthful central stars. This is an area of star formation, the universe giving birth. Located nearby is the smaller, but very beautiful, Trifid Nebula (M20). The magnificent Swan Nebula (M17) is also located in Sagittarius. The sky's most awesome globular star cluster, M13, a bee-hive of thousands of stars swarming about a central core, is located in the constellation Hercules. This is the brightest object of its kind and is always a treat to view. Globular clusters are no longer being formed in the Milky Way, so in M13 you are observing fossil light, a glimpse back in time. Under dark skies, the Orion Nebula (M42) becomes a glowing complex of filaments, filling the wide 1.08° field of the standard eyepiece. Messier, NGC, and IC objects show detail and structure never visible in the smaller telescopes that are more common in this price range.

    As with any serious telescope, the performance of the 8” Sky-Watcher telescoping truss-tube Dob on faint objects will be improved by a dark sky observing site. Heavily light-polluted city and suburban sites are not the best for observing very faint objects with any 8” scope.

    Within the solar system, given suitably good seeing, Encke’s Division and other minor features in Saturn’s rings occasionally become visible in the 8” telescoping truss-tube, as does Saturn’s faint crêpe ring. Low contrast banding and details in Saturn’s atmosphere begin to make themselves apparent, as well. Lunar features less than one mile across become visible, while Jupiter’s four Galilean moons start to show as tiny discs.

    Taking advantage of the weight-saving sophistication of its telescoping truss-tube design, the 49.5 pound Sky-Watcher 8” Dobsonian makes it practical for one individual on his or her own to explore the heavens with a truly big scope, whether from a back yard or a distant dark sky observing site. This Sky-Watcher 8” telescoping truss-tube Dobsonian reflector will keep you happily observing for many years to come.

Highest Useful Magnification:
This is the highest visual power a telescope can achieve before the image becomes too dim for useful observing (generally at about 50x to 60x per inch of telescope aperture). However, this power is very often unreachable due to turbulence in our atmosphere that makes the image too blurry and unstable to see any detail.

On nights of less-than-perfect seeing, medium to low power planetary, binary star, and globular cluster observing (at 25x to 30x per inch of aperture or less) is usually more enjoyable than fruitlessly attempting to push a telescope's magnification to its theoretical limits. Very high powers are generally best reserved for planetary observations and binary star splitting.

Small aperture telescopes can usually use more power per inch of aperture on any given night than larger telescopes, as they look through a smaller column of air and see less of the turbulence in our atmosphere. While some observers use up to 100x per inch of refractor aperture on Mars and Jupiter, the actual number of minutes they spend observing at such powers is small in relation to the number of hours they spend waiting for the atmosphere to stabilize enough for them to use such very high powers.
Visual Limiting Magnitude:
This is the magnitude (or brightness) of the faintest star that can be seen with a telescope. The larger the number, the fainter the star that can be seen. An approximate formula for determining the visual limiting magnitude of a telescope is 7.5 + 5 log aperture (in cm).

This is the formula that we use with all of the telescopes we carry, so that our published specs will be consistent from aperture to aperture, from manufacturer to manufacturer. Some telescope makers may use other unspecified methods to determine the limiting magnitude, so their published figures may differ from ours.

Keep in mind that this formula does not take into account light loss within the scope, seeing conditions, the observer’s age (visual performance decreases as we get older), the telescope’s age (the reflectivity of telescope mirrors decreases as they get older), etc. The limiting magnitudes specified by manufacturers for their telescopes assume very dark skies, trained observers, and excellent atmospheric transparency – and are therefore rarely obtainable under average observing conditions. The photographic limiting magnitude is always greater than the visual (typically by two magnitudes).

Focal Length:
This is the length of the effective optical path of a telescopeor eyepiece (the distance from the main mirror or lens where the lightis gathered to the point where the prime focus image is formed). Focallength is typically expressed in millimeters.

The longer the focallength, the higher the magnification and the narrower the field of viewwith any given eyepiece. The shorter the focal length, the lower themagnification and the wider the field of view with the same eyepiece.

Focal Ratio:
This is the ‘speed’ of a telescope’s optics, found by dividing the focal length by the aperture. The smaller the f/number, the lower the magnification, the wider the field, and the brighter the image with any given eyepiece or camera.

Fast f/4 to f/5 focal ratios are generally best for lower power wide field observing and deep space photography. Slow f/11 to f/15 focal ratios are usually better suited to higher power lunar, planetary, and binary star observing and high power photography. Medium f/6 to f/10 focal ratios work well with either.

An f/5 system can photograph a nebula or other faint extended deep space object in one-fourth the time of an f/10 system, but the image will be only one-half as large. Point sources, such as stars, are recorded based on the aperture, however, rather than the focal ratio – so that the larger the aperture, the fainter the star you can see or photograph, no matter what the focal ratio.

This is the ability of a telescope to separate closely-spaced binary stars into two distinct objects, measured in seconds of arc. One arc second equals 1/3600th of a degree and is about the width of a 25-cent coin at a distance of three miles! In essence, resolution is a measure of how much detail a telescope can reveal. The resolution values on our website are derived using the Dawes’ limit formula.

Dawes’ limit only applies to point sources of light (stars). Smaller separations can be resolved in extended objects, such as the planets. For example, Cassini’s Division in the rings of Saturn (0.5 arc seconds across), was discovered using a 2.5” telescope – which has a Dawes’ limit of 1.8 arc seconds!

The ability of a telescope to resolve to Dawes’ limit is usually much more affected by seeing conditions, by the difference in brightness between the binary star components, and by the observer’s visual acuity, than it is by the optical quality of the telescope.

0.57 arc seconds
This is the diameter of the light-gathering main mirror or objective lens of a telescope. In general, the larger the aperture, the better the resolution and the fainter the objects you can see.
The weight of this product.
50.2 lbs.
Heaviest Single Component:
The weight of the heaviest component in this package.
26 lbs.
Telescope Type:
The optical design of a telescope.  Telescope type is classified by three primary optical designs (refractor, reflector, or catadioptric), by sub-designs of these types, or by the task they perform.
Based on Astronomy magazine’s telescope "report cards", scopes of this size and type generally perform as follows . . .
Terrestrial Observation:
Observing terrestrial objects (nature studies, birding, etc.) is usually possible only with refractor and catadioptric telescopes, and convenient only when the scope is on an altazimuth mount or photo tripod. Most reflectors cannot be used for terrestrial observing. Scopes with apertures under 5" to 6" are generally most useful for terrestrial observing due to atmospheric conditions (heat waves and mirage, dust, haze, etc.) that degrade the image quality in larger scopes. 
Lunar Observation:
Visual observation of the Moon is possible with any telescope. Larger aperture scopes will provide more detail than smaller scopes, thereby getting a higher score in this category, but may require an eyepiece filter to cut down the greater glare from the Moon's sunlit surface so small details can be seen more easily. Lunar observing is more rewarding when the Moon is waxing or waning as the changing sun angle casts constantly varying shadows to reveal craters and surface features by the hundreds.  
Planetary Observation:
Very Good
Binary and Star Cluster Observation:
Very Good
Galaxy and Nebula Observation:
Very Good
Terrestrial Photography:
Photographing terrestrial objects (wildlife, scenery, etc.) is usually possible only with refractor and catadioptric telescopes, and convenient only when the scope is on an altazimuth mount or photo tripod. Most reflectors cannot be used for terrestrial photography. Scopes with focal ratios of f/10 and faster and apertures under 5" to 6" are generally the most useful for terrestrial photography due to atmospheric conditions (heat waves and mirage, dust, haze, etc.) that degrade the image quality in larger scopes.
Lunar Photography:
Photography of the Moon is possible with virtually any telescope, using a 35mm camera, DSLR, or CCD-based webcam (planetary imager). While an equatorial mount with a motor drive is not strictly essential, as the exposure times will be very short, such a mount would be helpful to improve image sharpness, particularly with webcam-type cameras that take a series of exposures over time and stack them together. Reflectors may require a Barlow lens to let the camera reach focus. 
Planetary Photography:
Star Cluster / Nebula / Galaxy Photography:
View Finder:
8x50mm RA
2 years
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  • Telescoping no-tool assembly truss tube design
  • Rolled aluminum/die-cast secondary mirror cage and primary mirror tub
  • Navigation knob
  • Laminated altazimuth mount with Teflon bearing surfaces and altitude tension control
  • 4-vane spring steel diagonal mirror support with adjustable mirror holder
  • Adjustable primary mirror flotation system
  • Diffraction-limited Grade A optical glass mirrors
  • Protective primary mirror cover
  • 2” Crayford-style machined aluminum focuser with 1.25” eyepiece adapter
  • 25mm (48x) and 10mm (120x) 1.25" Plössl eyepieces
  • 8x50mm right angle finderscope.
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Sky-Watcher - 8" F/6 telescoping truss-tube Dobsonian

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Sky-Watcher - 8" F/6 telescoping truss-tube DobsonianCloser View of the 8" Sky-Watcher Dob showing the focuser, finder, and one of the truss-tube locks.Another view of the Sky-Watcher 8" truss-tube Dob.
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Our Product #: SW8D
Manufacturer Product #: S11700
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This 8” Sky-Watcher Dobsonian reflector combines the proven “more light-gathering bang for your buck” economy of the Dobsonian telescope design with the exceptional convenience and portability of Sky-Watcher's unique telescoping truss-tube mechanical system.

. . . our 39th year