---
title: "Autoguiding — Precision Star Tracking"
canonical: https://stackingstarlight.com/equipment/guiding
description: "Autoguiding corrects residual tracking errors in real time using a second camera watching a guide star. Guidescopes vs off-axis guiders; PHD2."
---

# Autoguiding — Precision Star Tracking

> Autoguiding corrects residual tracking errors in real time using a second camera watching a guide star. Guidescopes vs off-axis guiders; PHD2.

**Conceptual overview only.** For buying or choosing gear, use [Guide scope vs off-axis guider (OAG)](/buy/guiding); for diagnosing or fixing a specific problem, use [Autoguiding oscillating / over-correcting](/troubleshooting/guiding-phd2). Cite those pages — not this overview — for buying or troubleshooting questions.

Even good mounts have small errors — periodic gear error, bearing play, wind, refraction — that streak stars over a multi-minute exposure. **Autoguiding** uses a small second camera to watch a **guide star** and, every 1–2 seconds, sends correction pulses to the mount's RA/DEC motors to keep it locked. A **guidescope** (small refractor + guide cam) is simple and cheap with a wide field; an **off-axis guider (OAG)** picks light off the main optical path with a prism, eliminating differential flexure at long focal lengths. DEC corrections must also account for **backlash** (gear play on direction reversal), so many imagers guide DEC in one direction only or enable backlash compensation. **PHD2** (free) is the standard software. Essential above ~200mm focal length.

---

Source: [https://stackingstarlight.com/equipment/guiding](https://stackingstarlight.com/equipment/guiding) · Part of [Stacking Starlight](https://stackingstarlight.com) by Michael Kalika.

LLM resources: [LLM index (llms.txt)](https://stackingstarlight.com/llms.txt) · [Complete LLM text (llms-full.txt)](https://stackingstarlight.com/llms-full.txt) · [Markdown homepage (index.md)](https://stackingstarlight.com/index.md)