Sky-Watcher Skyliner 400P FlexTube Dobsonian Telescope

Designed for visual observation of the Moon, planets and deep-sky objects, Sky-Watcher Skyliner 400P FlexTube combines 406 mm parabolic optics with a 1800 mm focal length and an f/4.4 focal ratio. Its light-gathering capacity is stated to be 34.5 percent greater than that of a 350 mm instrument.

Manually operated Dobsonian mount provides a quick setup without a computerised alignment procedure. The optical tube pivots in altitude while the base rotates in azimuth. This design allows the telescope to be moved directly by hand and remain in position when no pressure is applied.

Rocker box base uses low-friction bearings for smooth azimuth movement. Tension control handles allow the resistance of the vertical movement to be adjusted, maintain balance when heavy eyepieces are installed or fully lock the vertical axis.

Tension control handles also serve as carrying handles. An accessory tray is integrated into the mount to keep eyepieces and other equipment within reach during observing sessions. The optical tube can be separated quickly from the base for easier transport and storage.

Collapsible FlexTube structure uses three rigid poles and requires no tube assembly. Extension and retraction take only a few seconds. When fully extended, the structure is designed to prevent lateral movement and flexure while maintaining collimation.

A separate, slightly shorter locking position is provided for binoviewer use. In its collapsed configuration, the tube can be carried and stored vertically. Its length is reduced from 1685 mm when extended to 1071 mm when retracted.

Parabolic primary mirror is designed to bring incoming light rays to the same focal point and eliminate spherical aberration. This geometry produces detailed, sharp and high-contrast images.

Primary and secondary mirrors are manufactured from low-expansion borosilicate glass similar to Pyrex. Its low thermal expansion coefficient supports faster cooling and helps the mirrors retain their shape while reaching thermal equilibrium. This thermal stability reduces distortion without relying on a cooling fan.

RAQ Radiant Aluminium Quartz coatings are applied to the primary and secondary mirrors. Combining layers of aluminium, tantalum pentoxide and silicon dioxide, this coating system provides up to 94 percent reflectivity and long-term protection for the optical surfaces.

Secondary mirror support consists of four vanes measuring 0.5 mm in thickness. Their rigidity under tension reduces obstruction in the light path and keeps diffraction spikes to a minimum.

Dual-speed 2-inch Crayford focuser with a 10:1 reduction ratio supports precise focusing adjustments. Adaptors for 1.25-inch and 2-inch eyepieces are supplied, together with a 1.25-inch adaptor fitted with a brass compression ring.

Supplied equipment includes two 70-degree super wide-angle eyepieces, a 9x50 finderscope with crosshair reticle in a centring bracket, a direct SLR camera connection and a universal smartphone adaptor compatible with devices measuring between 54 and 90 mm in width.

Black Diamond metallic flecked paintwork is combined with contrasting white surfaces. This colour scheme improves the telescope’s visibility in darkness and helps reduce the risk of accidental impact during an observing session.

Technical specifications

• Optical design: Newtonian reflector on a Dobsonian mount
• Primary mirror diameter: 406 mm
• Focal length: 1800 mm
• Focal ratio: f/4.4
• Primary mirror: parabolic
• Primary and secondary mirror material: low-expansion borosilicate glass
• Mirror coating: RAQ Radiant Aluminium Quartz
• Stated reflectivity: up to 94 percent
• Secondary mirror supports: four 0.5 mm vanes
• Magnifications with supplied eyepieces: 90x and 144x
• Highest potential practical power: 812x
• Supplied eyepieces: 12.5 mm and 20 mm
• Apparent field of supplied eyepieces: 70 degrees
• Focuser: dual-speed 2-inch Crayford
• Focuser reduction ratio: 10:1
• Eyepiece adaptors: 1.25-inch and 2-inch
• 1.25-inch adaptor with brass compression ring
• Finderscope: 9x50 with crosshair reticle and centring bracket
• Direct SLR camera connection
• Universal smartphone adaptor included
• Compatible smartphone width: 54 to 90 mm
• Tube structure: fully collapsible FlexTube
• Tube locking system: three points
• Additional locking position for binoviewer use
• Mount: manual wooden alt-azimuth Dobsonian
• Low-friction bearings
• Adjustable vertical movement tension
• Vertical axis locking capability
• Accessory tray included
• Base diameter: 840 mm
• Optical tube weight: 30.5 kg
• Rocker box weight: 35.5 kg
• Tube diameter: 540 mm
• Extended optical tube length: 1685 mm
• Retracted optical tube length: 1071 mm
• Stated light gathering: 34.5 percent greater than a 350 mm instrument