Star tracker or equatorial mount? Choosing a mount for astrophotography

2 November 2026 · 3 min read

Every deep-sky image depends on the mount. It has to turn smoothly at exactly the speed the sky does, for minutes at a time, while carrying your camera and optics. There are three main kinds, and the right one depends mostly on your focal length.

Star trackers

A star tracker is a small, motorised mount that rotates a camera around an axis pointed at the celestial pole. Examples include the iOptron HST MiniTracker and similar compact mounts.

• Best for: camera lenses and very small refractors, roughly up to 250–300 mm, and travel.
• Payload: a few kilograms. Keep well under the rating; around 70% is a sensible imaging limit.
• Limits: above about 500 mm, small tracking errors become visible as trailed stars, and you'll throw away many frames.
• Why choose one: light, cheap, runs on small batteries, fits in hand luggage.

Worm-gear equatorial mounts

The classic German equatorial mount (GEM), such as the iOptron GEM28 and CEM40 or the Celestron CGX, drives each axis through a worm gear and balances the load with counterweights.

• Best for: refractors, Newtonians and SCTs from about 300 mm up to 2000 mm or more, with guiding.
• Payload: much higher, but plan on using about 50–60% of the rating for imaging. Gear backlash and wind make a heavily loaded worm mount struggle.
• Limits: heavy. A Celestron CGX head alone (20 kg) weighs more than most rigs, plus counterweights and a tripod.
• Why choose one: the most capacity for the money, and proven designs with years of community support.

Strain-wave (harmonic) mounts

Strain-wave mounts such as the iOptron HEM15 and HEM27 use a harmonic drive instead of a worm gear. They're compact for their capacity and can carry a full load without counterweights.

• Best for: portable setups from small refractors up to compact SCTs, almost always guided.
• Payload: close to the rating works well for imaging, around 80%, because there's no backlash to balance against.
• Limits: their periodic error is fast and irregular, so guiding is effectively required for long exposures. They cost more than a worm mount of similar capacity.
• Why choose one: a heavy-duty mount you can carry in one trip.

Rules of thumb

Whatever you choose, polar alignment matters. A mount that isn't aligned to the celestial pole will drift and rotate the field, however good its gears.

Check your mount against your rig

RigTonight adds up the weight of every part on the mount (telescope, corrector, camera, filter wheel, guide scope, controller, plus rings, cables and dew straps) and compares it with a realistic imaging limit for that type of mount. It also warns when a tracker is carrying too much focal length, and when guiding would help. How much can your mount really carry? shows the sums.

Choosing the rest of the rig? How to build an astrophotography rig goes through every part in order, and the best beginner setup pairs each kind of mount with a telescope and camera.