autoguiding

Autoguiding is an astronomical technique used to correct the small tracking errors of a telescope mount during long-exposure imaging. It relies on a guide camera that images a bright star and guiding software that sends real-time corrections to the mount to compensate for imperfect tracking, periodic error, wind, and flexure.

Typically, a guide scope or an off-axis guider is used. Light from a guide star is focused onto the guide camera; software tracks the star's position and computes drift in right ascension and declination. Corrections are transmitted to the mount's guiding port at short intervals to reduce trailing in the main image.

Calibration and workflow: a short calibration sequence measures how the mount responds to guide pulses in each axis, allowing accurate corrections. During a run, guiding may be combined with dithering or multi-star guiding to improve robustness against field distortions.

Components: guide scope or off-axis guider, guide camera, mount with a guiding interface, and guiding software such as PHD2, Maxim DL, or compatible drivers. The system is widely used in amateur and professional settings to enable longer exposures.

Applications and limitations: autoguiding is essential for long-exposure astrophotography and spectroscopy, reducing star trailing caused by mount errors. Performance depends on guide-star brightness, atmospheric seeing, mount stiffness, calibration accuracy, and mechanical stability; poor conditions or miscalibration can limit effectiveness.

History: autoguiding has developed since the late 20th century with the advent of CCD and CMOS guide cameras. Modern software and hardware have made real-time guiding accessible to amateurs, expanding the capability to obtain high-quality deep-sky images.