Autoguiders & Trackers: What Actually Corrects Your Tracking
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Two Different Problems, Two Different Tools
"Tracker" and "autoguider" get used almost interchangeably by beginners, but they solve different problems for different setups — and buying the wrong one for what you're actually trying to do is a common, avoidable frustration.
A star tracker is a small motorized mount built for wide-field astrophotography with a camera and lens — no telescope required. It rotates at the same rate as the sky, roughly counteracting Earth's rotation so stars stay as sharp points instead of trailing during a multi-second or multi-minute exposure. It's a complete, self-contained solution for Milky Way shots, nightscapes and wide-field nebula images.
An autoguider solves a narrower, more demanding problem: keeping a telescope's equatorial mount precisely on target during long deep-sky exposures, where even a tracker-grade mount will drift or exhibit periodic error over several minutes. An autoguider is a second, smaller camera — usually attached to a separate guidescope or an off-axis guider sharing the main telescope's light path — that continuously watches a guide star and sends real-time correction pulses back to the mount's motors, many times per second. It doesn't replace the mount; it corrects it.
In short: a tracker is the mount. An autoguider is the feedback loop that keeps a more advanced mount honest during long telescope exposures. Most imagers start with a tracker, and only add an autoguider once they move from wide-field camera shots to telescope-based deep-sky imaging.
ZWO ASI120MM-Mini: A Dedicated Autoguiding Camera
The ASI120MM-Mini is one of the most widely used entry points into autoguiding — a small, inexpensive monochrome camera purpose-built to run alongside guiding software rather than to capture images on its own. Paired with a guidescope or an off-axis guider and free software like PHD2, it watches a guide star and reports drift back to the mount in real time.
| Sensor | 1/3" CMOS, Monochrome |
| Resolution | 1.2 MP (1280 × 960) |
| Pixel Size | 3.75 µm |
| Guide Output | ST4 port |
| Connection | USB 2.0 |
| Price | Approximately $100–$120 USD |
This piece isn't a first-hand test — ORIVON has not put an ASI120MM-Mini unit through its own trial period. What follows draws on published specifications and patterns in buyer and reviewer feedback around ZWO's guide camera lineup, which the ASI120MM-Mini has anchored for years as the low-cost, high-compatibility option.
Already Have a Star Tracker? Here's the Other Half
If your setup is a camera and lens on a portable tracker, an autoguider isn't the next purchase — the tracker's own build quality and polar alignment accuracy matter far more at that stage. The Sky-Watcher Star Adventurer 2i Pro Pack, which we've reviewed separately, remains our reference recommendation in that category: a compact, app-controlled tracker with the periodic error performance to hold wide-field exposures well past what most beginners need before they'd even consider adding a telescope and a guiding setup on top of it.
Read the full review of the Sky-Watcher Star Adventurer 2i Pro Pack →
Who Needs an Autoguider
Based on this editorial analysis — not on direct testing by ORIVON — an autoguider makes sense once you're imaging through a telescope at a focal length long enough that your mount's unguided tracking starts showing round stars turn oval over exposures of a minute or more. If you're still shooting wide-field with just a camera and lens, a good tracker alone is the correct — and sufficient — tool.
Frequently Asked Questions
Not typically — autoguiding assumes a telescope-grade equatorial mount with a guide port. Most star trackers aren't designed to accept external guiding corrections.
Either works with the ASI120MM-Mini. A separate guidescope is simpler to set up; an off-axis guider avoids differential flexure and is generally preferred at longer focal lengths.
No — it's a second-stage upgrade. Most imagers spend their first season or more on wide-field tracker imaging before a telescope and guiding setup become relevant.