Sky-Watcher EQ8-Rh Mount Head Only with Counterweights

Sky-Watcher EQ8-Rh: A 50 kg Foundation for Astrophotography

The EQ8-Rh offers a 50 kg (110 lb) payload capacity, excluding the two included 10 kg counterweights. There is no list of compatible telescopes: add up the tube, camera, guide scope and accessories and compare the total with the rating.

As an equatorial mount, it tracks with its polar-aligned R.A. axis. The mount head itself weighs 25.8 kg (56.9 lb).

The Renishaw R.A. Encoder: 0.11 Arc-Second Resolution

The EQ8-Rh carries a Renishaw high-resolution incremental encoder on the Right Ascension axis. Sky-Watcher marks it as available on the EQ8-RH only. It reads the axis at a resolution of 11,840,000 counts per revolution, or about 0.11 arc-seconds.

This encoder helps to reduce or eliminate the influence of mechanical periodic error while the mount is tracking an object. The mount also keeps the 200-segment permanent PEC described below.

Drive System: 0.9° Stepper Motors and a 435:1 Worm Drive

The EQ8-Rh's motion is controlled by 0.9° hybrid stepper motors. These motors drive a 435:1 worm gear transmission on each axis. This combination, with 256 microsteps per motor step, gives a resolution of 44,544,000 counts per revolution, or approximately 0.03 arc-seconds.

Balancing the Load

Balance the mount to reduce stress on the motor drive system and to ensure smooth and accurate operation. The EQ8-Rh includes two 10 kg (22 lb) counterweights and a 2.6 kg (5.7 lb) counterweight rod. The balancing procedure involves adjusting both the counterweights on the rod and the telescope's position in the saddle.

First, loosen the R.A. clutch, turn the axis until the counterweight rod is parallel to the ground and slide the counterweights until the axis stays put. Next, loosen the Dec. clutch and adjust the telescope's dovetail bar forward or backward within the D-style saddle until the tube stays put.

Polar Alignment from 15° to 65° Latitude

The EQ8-Rh has a latitude range from 15° to 65°, adjusted with a jackscrew (handle included), and two azimuth adjustment knobs with a ±10° range.

The polar scope is optional. The SynScan V5 hand controller can show the polar alignment error after a 2-star alignment, and its polar alignment routine (no polar scope needed) slews to a reference star and guides you through the altitude and azimuth adjustments.

SynScan V5 GoTo: 42,000+ Objects at 3.7° Per Second

The included SynScan V5 hand controller is the primary interface for the EQ8-Rh. Its database contains over 42,000 celestial objects, including the Messier, NGC, IC and Caldwell catalogs, as well as SAO stars, double stars, and planets. After a 1-star, 2-star or 3-star alignment, it slews to objects in its database with a pointing accuracy of up to 5 arc-minutes (RMS).

The mount can slew between targets at a maximum speed of 3.7° per second. It supports standard tracking rates for sidereal, solar, and lunar targets, and offers a range of autoguiding speeds from 0.125x to 1x sidereal.

ASCOM, USB, and App Control for Remote Imaging

The control panel features a USB port that provides a direct USB-to-serial connection for controlling the mount from a PC. All of Sky-Watcher's control options support the ASCOM platform.

Alternatively, you can control the mount wirelessly by adding the optional SynScan Wi-Fi dongle. This enables control via the SynScan Pro app, for iOS, Android or Windows. On Windows and Android the app also works over the built-in USB port.

PPEC, Auto-Home, and Camera Control for Automation

The 200-segment Permanent Periodic Error Correction (PPEC) lets you train the mount (manual or auto-guiding) and stores the data permanently in the motor controller. This means a new training run is not needed for each session, assuming polar alignment is accurate. It improves tracking for short focal length astrophotography.

• Auto-Home Function: Two built-in home position sensors allow the mount to return to a precise, repeatable starting position on command from the SynScan controller.
• Autoguide Port: A standard ST-4 compatible autoguide port works with any autoguider with an ST-4 type interface.
• SNAP Shutter Release: A dedicated SNAP port allows the SynScan controller to trigger a DSLR camera's shutter. The mount includes a cable for Canon EOS models, and the controller's "Camera Control" function takes up to 8 groups of exposure-time and frame settings.

Through-Mount Cable Management and D-Style Saddle

The EQ8-Rh has an integrated cable management system. Power and data ports on the stationary part of the mount (IN panel) are routed internally to a corresponding set of ports on the moving declination axis (OUT panel).

The system includes passthroughs for auxiliary power, USB, and paired RJ10, RJ12, and RJ45 jacks. The mount is topped with a D-style saddle, with three knobs, tightened alternately, to hold the telescope's dovetail bar. For safety, both the R.A. and Declination axes are equipped with internal hard stops that protect the mechanical parts, the optical tube and the internal wiring.

Powering the EQ8-Rh: 11-16V DC and 55W Minimum

The mount requires a DC power source providing between 11V and 16V, with a minimum power output of 55W. A higher voltage within this range is preferred for optimal motor performance, and Sky-Watcher's 13.7V/4A AC-to-DC switching supply is highly recommended. Do not use an unregulated AC-to-DC adapter.

The control panel's LED provides a quick status check on the input voltage. A steady light indicates normal power, while slow flashing warns of low voltage, and fast flashing indicates an extremely low voltage that could damage the battery or motor controller.

Assembly and Portability: A 25.8 kg Mount Head

The mount head weighs 25.8 kg (56.9 lb), the counterweight shaft is 2.6 kg (5.7 lb), and the two included counterweights are 10 kg (22 lb) each. Setting up involves placing the mount head onto a suitable pier or tripod, attaching the counterweight shaft and counterweights, and then mounting the optical tube assembly.

The jackscrew handle and a 6 mm Allen wrench are included. Then balance the mount and polar-align it.