PHD3

PHD3 is a free, open-source autoguiding application used in astronomical imaging to improve the accuracy of telescope guiding during long exposures. By analyzing images from a guide camera, it tracks the position of a bright guide star and computes small, continuous corrections to the telescope mount, reducing drift and periodic error in the main imaging exposure.

Designed as a successor to earlier PHD guiding software, PHD3 emphasizes robust operation, real-time analysis, and user-friendly controls. The software supports real-time centroiding of guide stars, automatic calibration, and features such as optional dithering to introduce small intentional shifts between frames to improve guiding performance and avoid sensor noise patterns. It can monitor multiple guide stars and allows scripting and advanced logging for troubleshooting.

PHD3 is cross-platform, running on Windows, macOS, and Linux, and interfaces with common mount control ecosystems, including ASCOM on Windows and INDI on other platforms, as well as direct drive protocols for several widely used mounts. It accepts input from a variety of guide cameras and can integrate with popular astronomical imaging suites and schedulers.

Development of PHD3 is community-driven, with the project hosted on public repositories. It continues to be maintained and updated by volunteers, building on the legacy of the original PHD guiding software and serving a dedicated user base in the amateur astronomy community.