Sky-Watcher FlexTube 200mm Dobsonian Telescope

• Ideal instrument to make the most of deep sky observation
• Versatile planetarium (Moon, planets) and deep sky (galaxies, nebulae)
• Foldable to avoid complete disassembly and collimation
• Easily transportable by a single person (tube + base)

In recent years, Dobson fever has increasingly invaded amateur astronomers aware that the strongest sensations are felt with large diameter telescopes. In fact, observation of the planets is limited to Jupiter, Mars, Saturn (and the Moon), while clusters, nebulae and galaxies are counted in the hundreds on a 200mm instrument (see thousands for the largest diameters under a dark sky). Without motors or electronics, Dobsonians are in fact the instruments that provide the most light, on a given budget, compared to any other type of instrument (mostly motorized and Go-To).

However, the search for diameter creates a big drawback: size! When you want to observe in the best conditions, to exploit the full potential of your instrument, away from the light of cities, it is imperative to transport your equipment in a vehicle and then assemble and disassemble it. However, space is needed and, if possible, a minimum of back-and-forth during loading. Although Serrurier structures have been around for a long time, they have only recently become available on inexpensive Dobsonians and require permanent disassembly/assembly and then re-collimation (an operation that takes a little time but which you eventually get used to with experience) .

Sky-Watcher, which has been designing solid tube dobsonians that have been popular with beginners and hobbyists for many years, innovated in 2009 by completely adopting the design of its instruments. The Chinese-Canadian manufacturer has sought to combine the "complete assembly" advantage of solid tubes and the small size provided by open tubes. The idea of ​​the "telescopic telescope" is now a reality (at a price that remains very attractive) through the FlexTube range.

According to the principle that " the best instrument is the one we use most frequently ", SkyWatcher takes comfort even further with the FlexTube range so you don't hesitate for a moment to contemplate the sky and its wonders.

FlexTube: maximum comfort

The principle of the FlexTube is simple, it is based on a locksmith-type design, where 3 tubes solidly support the secondary mirror cage (which also supports the focuser and finder). Except here The tubes are not removable because they are housed in a clamp that allows them to slide . By simply loosening 3 knobs, the tubes slide down until the instrument folds. Three screws into the secondary cage then fix it to the main body. The set is much "smaller" and fits easily, vertically, in the trunk of any car (maximum height of 920 mm for the 305 mm one). With a 630x740 mm base, you'll even have room for several accessories.

The important point of such a configuration is the behavior of collimation (alignment between the 2 mirrors). According to the manufacturer, The FlexTube preserves the position of the 2 optical elements (particularly the secondary mirror) in each folding/unfolding . Note: The alignment does not change at night or depending on the position of the optical tube. Therefore, there is nothing easier than establishing such instruments. Take out the entire telescope using the handles (height adjustment knobs) (40 kg total for the largest model). Loosen the tube tightening knobs (as well as the locking screws). Slide the mirror cage to the tube stop position. Tighten the knobs to finish.

With no setup required, your telescope is ready for a night of observing full of discovery. (if you haven't touched the focuser since your last outing, then the focuser is already "ready"). In just a few seconds you will have completed/avoided the traditional steps: telescope exit/mounting/collimation. Save more time and enjoy unmatched convenience!

For information: Check, for safety (to be sure to benefit from the full performance of your optics), the collimation because the primary mirror can move slightly if it is moved with the help of a car (common to all telescopes normally Dobson, Cassegrain or Newton). Using a cheshire or blurring the focus on a bright star.

Mechanical concept

Sky-Watcher not only offers telescopes at very advantageous prices, but also easy-to-use instruments, as demonstrated by the tilt system that is installed on all Dobsonians from 150 to 305 mm. In fact, the Chinese-Canadian firm has developed and patented (US Patent No. 6,940,642) a handle that allows you to tighten or loosen the fork on the optical tube. Thus, depending on the inclination of the tube and the weight of the accessories present in the eyepiece holder (binocular head, eyepieces of different angles), the observer can increase or decrease the friction. The tube is then supported enough to not tilt downwards. as with other constructions and free enough to be easily oriented towards another place in the sky.

Unlike very cheaply made or Newtonian telescopes with small diameters, The 203 to 400 mm Newton (Dobson) Sky-Watcher have a parabolic primary mirror . The mirrors are polished spherically and then trimmed to achieve a paraboloid shape (more expensive and difficult to obtain). This is an essential selection criterion for instruments above 130 mm and with a short f/D.

Regarding the material used for the primary mirror, the 203/254/305/355/406 mm are made of Pyrex , which has the effect of reducing expansion effects due to thermal changes. In fact, the thermal expansion coefficient is lower than standard glass, which reduces its warm-up time and ensures better image quality. Like the secondary, the primary is coated with layers of titanium dioxide (SiO2) and quartz (SiO4) for effective protection.

An achromatic viewfinder on its support is also supplied as standard. With a large diameter of 50mm for 9x magnification, it reveals objects invisible to researchers of smaller dimensions for a much easier search. Two eyepieces of 25mm and 10mm focal length will allow you to start, initially, by having a good magnification range compatible with all possible objectives.

Tuning for 203, 254 and 305 mm FlexTube Dobsonians

Focusing is achieved through a Crayford bi-flow focuser. A 31.75mm adapter is supplied as standard to use eyepieces of the same format from the 50.8mm output. A clamping screw located on the bottom of the focuser helps maintain focus according to the orientation of the optical tube.

Specifications