Sky-Watcher Flextube 400P SynScan

GoTo on a Collapsible Dobsonian

The SynScan hand control can point the telescope at a chosen object or tour the sky at the touch of a button, and the motors track the object once found. Even an inexperienced astronomer can master its features in a few observing sessions.

406mm f/4.4 Optics

The 406mm primary mirror has an 1800mm focal length, giving f/4.4. The highest practical power is 812x.

Optical details:

• Primary mirror: paraboloidal, 406mm.
• Secondary mirror: 102mm (Sky-Watcher USA).
• Eyepieces: 20 mm (90x) and 12.5 mm (144x), 1.25-inch.

Collapsible Tube: 1685mm to 1071mm

The 30 kg tube is 540 mm in diameter and 1071 to 1685 mm long (skywatcher.com). Unlike other truss designs, Sky-Watcher's collapsible Dobsonian does not need to be disassembled between uses: it transports as two compact pieces, is ready to use in seconds, is easy to collimate once set up and holds collimation throughout the evening.

Level the round base, loosen the three slider lock screws and pull the top tube out until it clicks, then tighten the screws without over-tightening. Remove the dust cap and front cover, lift the tube at the indicated positions onto the mounting platforms inside the side boards, and tighten the locking screw.

Dobsonian Base and Freedom Find

The base weighs 105 lb and measures 36" x 34". The base comes flat-packed and is assembled with the screws, Allen wrenches and Phillips screwdriver supplied.

Sky-Watcher's patented Freedom Find dual-encoder technology lets you move the telescope by hand or electronically in either axis without losing its alignment or position information. Each axis has one encoder on the axis shaft and one on the motor shaft. After you move to a new object, the telescope begins tracking it, with no re-setup in one observing session.

SynScan GoTo, Tracking and Power

The SynScan hand control can point the telescope at a chosen object or tour the sky at the touch of a button; its menu system slews automatically to over 42,900 objects: the complete Messier (110) and Caldwell (109) lists, 7,840 NGC and 5,386 IC objects, 29,523 SAO stars, 212 named stars, 55 double stars, 20 variable stars, the planets, and up to 25 user-defined coordinates.

GoTo pointing accuracy is up to 5 arc minutes.

• Alignment: Brightest-Star or Two-Star alignment; choose stars at least 60 degrees apart in azimuth.
• Tracking: sidereal, lunar and solar rates in dual-axis tracking mode, driven by DC servo motors.
• Slew speeds: ten, from 1x to 1000x; the manual suggests Rate 4 for centering in the finderscope and Rate 3 or less in the eyepiece.

Computer Control

An RS-232 cable connects the hand control's RJ-12 port to a computer at 9600 bits per second.

The firmware is user upgradable from version 3.0, and the manual says version 3.00 and later work with the Celestron NexStar 5i/8i and NexStar GPS command protocol, which planetarium software can use to drive the mount.

Power

Power: 10 to 15 V DC at 1 A, through a 2.1 mm center-positive plug into the Power jack on the altitude motor box. A 12V DC car-lighter power cable is included; the battery or power supply is sold separately.

To avoid tangling the power cable, the manual suggests placing the battery pack or power tank on the round base, behind the front panel.

Two-Star Alignment

Align the 9x50 finderscope with the tube first. Then enter your location, date and time and choose 2-Star Align. Pick a star you can identify from the list, center it in the finder and then the eyepiece, and press ENTER. Choose the second star; the mount slews near it, and you center it with the direction keys and press ENTER.

Focuser, Finder and Eyepieces

The 2" dual-speed Crayford focuser takes 2-inch eyepieces and comes with a 1.25" eyepiece adapter.

A 20mm and a 12.5mm 1.25-inch eyepiece, a 9x50 straight-through finderscope, dust caps and the car-lighter power cable are included.

Tube and Base

The tube weighs 30 kg (skywatcher.com) and the base 105 lb (Sky-Watcher USA). They transport as separate pieces: retract the tube, loosen the locking screw and lift it off the base.

The collapsible design is easy to collimate once set up and holds its collimation throughout the evening.

Solar Safety

Never use the telescope to look directly at the Sun, as permanent eye damage will result. Use a proper solar filter for viewing the Sun.

When observing the Sun, place a dust cap over the finderscope. Never use an eyepiece-type solar filter, and never use the telescope to project sunlight onto another surface: the internal heat build-up will damage the optical elements.