Sky-Watcher Flextube 300P 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.

305mm f/4.9 Paraboloidal Optics

The 305mm paraboloidal primary mirror has a 1500mm focal length, giving f/4.9, with a 70mm secondary mirror. The highest practical power is 610x.

Collapsible Tube: 1400mm to 920mm

The 21 kg tube is 450 mm in diameter and 920 to 1400 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. Sky-Watcher's patented tension control handle adds or reduces friction on the tube.

Freedom Find Dual Encoders and Motors

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; the motor encoders have 1,620,000 counts per revolution and the main axis encoders 11,748.

After you move to a new object, the telescope begins tracking it, with no re-setup in one observing session. DC servo motors drive both axes with ten slew speeds from 1x to 1000x, track at sidereal, lunar or solar rate in dual-axis mode, and give GoTo pointing accuracy of up to 5 arc minutes.

SynScan Database and Alignment

The 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. The TOUR key takes you on a preset tour of the sky you are under.

Before GoTo, level the base, align the finderscope, and align the system on two stars:

• Brightest-Star alignment: recommended if you are new to the sky. Choose one of eight regions of the sky; the hand control lists the stars brighter than magnitude 1.5 there, you center the first, and the mount slews to a second for you to center.
• Two-Star alignment: choose two stars from a list, at least 60 degrees apart in azimuth.

Computer Control

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

The hand control firmware is user upgradable from version 3.0, and the hand control can also display the motor control board's firmware version.

Power

The mount needs 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 pack 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.

Assembly and Setup

The base comes flat-packed: attach the feet to the round base, then the side panels with their reinforce boards (fixed with eight M5x60 hex socket cap screws), the front panel, handles and motor boxes, using the screws, Allen wrenches and Phillips screwdriver supplied.

For each session, level the round base with a bubble level, 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 by the indicated positions onto the mounting platforms inside the side boards, and tighten the locking screw. Connect the power and hand control cables, enter your location, date and time, and align.

Focuser, Finder and Eyepieces

The 2" single-speed Crayford-style focuser comes with a 2" to 1.25" eyepiece adapter. A 9x50 straight-through finderscope, dust caps and a 12V DC car-lighter power cable are included.

The two 1.25-inch eyepieces:

• 20mm eyepiece: 1500 / 20 = 75x.
• 12.5mm eyepiece: 1500 / 12.5 = 120x.

Tube, Base and Care

The tube weighs 21 kg (skywatcher.com) and the base 53 lb (Sky-Watcher USA), which lists the base at 32.5" x 25". They transport as two 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. Keep the dust caps on when the telescope is not in use.

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.