Autoguider

Specifications

Observing parameters

Overview

Strictly, "autoguider" means the closed loop: a guide camera, a driver interface to the mount, and software that measures the guide star's centroid each frame and issues corrections. The result is that exposures measured in minutes become possible on a mount whose periodic error would otherwise smear the stars in thirty seconds.

Setup is calibration — the software drives the mount in each axis and measures how many pixels of star movement correspond to how many milliseconds of pulse, which also establishes the angle between the guide camera and the mount axes. Get calibration wrong and guiding will actively make things worse.

Watch the RMS figure. Below about 1 arcsec is good with typical amateur gear, and below the image scale of your main camera is the actual requirement — there is no point guiding to 0.4 arcsec if your pixels cover 2 arcsec.

Where it fits

Practical notes

• Calibrate near the meridian and near the target's declination; calibration is position-dependent.
• Re-calibrate after a meridian flip — the guide camera's angle relative to the mount has changed.
• Measure backlash and enter it; guessing here produces oscillation rather than correction.
• Turn on dithering. It costs almost nothing and removes fixed-pattern noise from the stack.

Pairs with

• Guide Scope
• CMOS Camera
• Equatorial Mount
• Dew Heater