iOptron GEM28 Mount

A Payload-to-Weight Ratio of 2.80

The all-metal, CNC-machined structure is built around robust Φ35mm steel axis shafts and large Φ55mm ball bearings. The payload-to-weight ratio is 2.80.

28 lb Capacity with a Single 10 lb Counterweight

The GEM28's payload is 28 lb (12.7 kg), excluding counterweight. It depends on OTA size and length, and tubes smaller than 6" in diameter are recommended. The mount includes a single 10 lb (4.5 kg) counterweight, a Φ20 x 200mm stainless steel counterweight shaft, and a 120mm shaft extension. The supplied counterweight should be sufficient for a 6" scope with total payloads up to about 12 lbs; use extra counterweight or the extension bar to balance more.

Φ88mm Worm Wheels and Belt-Driven Stepper Motors

Each axis is driven by a 1.8º stepper motor with 128x micro-stepping (0.17 arc second resolution). A synchronous belt transmission transfers power to the brass worm gears, which engage large Φ88mm, 144-tooth aluminum worm wheels. The worm period is 600 seconds.

<±12 Arcsecond PE with Permanent PEC

Out of the box, the standard GEM28 mount has a native periodic error of less than ±12 arcseconds. The mount's Permanent Periodic Error Correction (PPEC) lets the hand controller record the periodic error, for example while autoguiding, and play back the correction. PEC is especially useful when doing astrophotography without autoguiding.

iPolar and AccuAlign Options for 10º to 70º Latitudes

Accurate polar alignment is essential for a German equatorial mount, and the GEM28 offers two solutions across a wide 10º to 70º latitude adjustment range. AccuAlign versions have a dark-field optical polar scope, used with the hand controller's Quick Polar Alignment. iPolar versions have the internal iPolar electronic polar scope, which connects to a computer by USB; it ensures accurate alignment even when the pole star is obscured.

The Go2Nova 8409 Controller and its ~212,000 Objects

The included Go2Nova 8409 hand controller is your command center for navigating the sky. Its database contains approximately 212,000 objects. The controller offers nine slew speeds, from a fine-positioning 1x sidereal rate to a rapid 6º per second MAX speed for moving quickly between targets. It also handles PEC recording, and the mount has power-down memory.

Built-in Wi-Fi, USB, and ST-4 Autoguiding

The GEM28 has built-in Wi-Fi for wireless control and a USB port for a wired connection, with control through the iOptron ASCOM driver. There is an ST-4 compatible autoguide port.

The 3.8" Vixen-Style Dovetail Saddle

The telescope mounts on a 3.8" spring-loaded Vixen-style dovetail saddle with a center adjusting block, which accommodates dovetail bars of different widths and keeps the tube centered.

12V DC Operation Drawing 0.6A While Tracking

The GEM28 runs on 12V DC, 5A, drawing 0.6A during tracking and 0.9A during GoTo. A 100V-240V AC adapter is included. The mount is rated for operation in temperatures from -10ºC to 40ºC.

GEM28 vs. GEM28EC: Real-Time PEC for <0.3 Arcsecond RMS Error

The GEM28EC model adds a high-resolution encoder on the Right Ascension axis.

• Lower Periodic Error: The GEM28EC has a periodic error of <0.3 arcseconds RMS.
• Real-Time PEC: Instead of relying on a pre-recorded PPEC curve, the GEM28EC's encoder provides Real-time Periodic Error Correction.

Tripod Options: The 1.5" Standard vs. the 7.5kg LiteRoc

The GEM28 is sold with one of two tripods.

• 1.5" Stainless Steel Tripod: Weighs 5kg.
• LiteRoc Heavy-Duty Tripod: A heavy-duty stainless steel tripod weighing 7.5kg.