SkyWatcher 254mm Dobsonian Telescope

• Large diameter ideal for deep sky observation
• Versatile planetary (Moon, planets) and deep sky (galaxies, nebulae)
• Transportable by a single person.

Everything you need to know about the Sky-Watcher 254mm f/4.7 Dobsonian telescope

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 254 mm instrument (or even in the thousands for the largest diameters). under a dark sky). Without motor or electronics, Dobsons are in fact the instruments that provide the most light, on a given budget, compared to any other type of instrument. (mainly motorized and Go-To). Sky-Watcher has been designing solid tube Dobsons for many years, appreciated by beginners and hobbyists in a range extending from 150mm to 305mm.

Hobbyists will appreciate the 200 and 254mm because they are capable of showing many more objects in greater detail. They belong to the range of instruments that can be kept for many years before reaching their limit. . It is also possible to combine them with O-III or UHC filters to see the most beautiful nebulae from another perspective (more contrast, less light pollution). The 305mm offers fantastic views of thousands of objects (NGC/Messier catalogues). Nebulae, globular clusters and galaxies will be easily accessible.

For visual observation enthusiasts, it is the best performance/price ratio! Treat yourself to a “real” telescope without delay. Guaranteed emotions, minimal investment!

Optical design

The Newton design offers several advantages compared to other families of instruments (Cassegrain glasses and telescopes). Firstly, mirrors are cheaper to manufacture for the same diameter and their focal ratio is generally very low. This way, you can benefit from a very attractive quote for a brilliant telescope. which provides an almost coma-free field in the 200 mm model (the 254 and 305 mm, with their short focal ratio, can be complemented with a coma corrector). The central obstruction is weaker than that of Cassegrain-type telescopes, if collimation (mirror adjustment) is respected, the image quality is good in planetary mode. The Dobson mount also significantly reduces the price of this telescope compared to motorized equatorial mounts.

Unlike very cheaply made or small diameter Newton telescopes, the 150, 203, 254 and 305 mm Newton (Dobson) Sky-Watcher telescopes have a mirror parabolic primary. The mirrors are polished spherically and then trimmed to achieve a parabolic shape (more expensive and difficult to obtain). This is an essential selection criterion for instruments larger than 130 mm and with short f/D .

Mechanical concept

Sky-Watcher not only offers telescopes at very advantageous prices, but also easy-to-use instruments, as demonstrated by the tilt system fitted to all 150 to 305 mm Dobsonians. In fact, the Chinese-Canadian company has developed and patented (US Patent No. 6,940,642) a handle that allows the fork to be tightened or loosened 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 flux) the observer can increase or decrease the friction. The tube is then secured enough to not tilt downwards. as is the case with other manufacturers and free enough to easily point it towards another place in the sky.

Focusing is achieved through a bi-flow eyepiece . A 31.75mm adapter is supplied as standard to use eyepieces of the same format from the 50.8mm output. An adjustment screw located on the top of the eyepiece holder allows you to maintain focus by following the orientation of the optical tube. Also delivered as standard a 9x50 achromatic finderscope on its stand. With a large diameter of 50mm at 9x magnification, it reveals objects invisible to the smallest researchers.

Regarding the material used for the primary mirror, 254mm and 305mm Dobsonians benefit from Pyrex glass which has the effect of reducing the effects of expansion due to thermal changes. In fact, its coefficient of thermal expansion is lower than that of standard glass, which reduces its warm-up time and guarantees better image quality.

Specifications