Written byon Dec. 5, 2012 .
Autoguiding – Advanced Techniques
András Dán, MSc, Gemini, Nov. 2012.
It is time we take a systematic approach at this very important topic of astrophotography to get the most out of our expensive gear – mount, guide scope, guide camera, main camera.
The aim of this document is to help understanding the process of autoguiding and to get the best result possible with your gear. It is intended for both beginners and experts.
Autoguiding is an attempt to track the sky with smaller error than the pixel scale (smallest visible error) of our imaging (main) camera. While trying to correct mount errors we want to disregard seeing blur (except with active optics using high frequency).
Let's start by creating a list of the players of the game.
Guide star – its position on the guide chip is measured by the guide software at regular intervals, normally with a few seconds (1-5) of integration. The measured so called “guide error” is the result of mount tracking errors (refraction and mechanical errors) and seeing blur.
Mount – it tracks the sky as precisely as its polar alignment, software and mechanics allow.
Guide camera – it takes images of the guide star and sends them to the guide software for analysis.
Guide scope (separate) – images the guide star for the guide chip. In case of off axis guiding or dual chip camera we have no guide scope.
Guide software – this is the brain of the system, interprets the guide chip data and sends guide commands to the mount.
Main telescope – don't blame everything on the guider, the main telescope is half of the story
It all starts with taking an integration of the guide star. Let this be 2 sec.
When finished, the image is downloaded and analyzed by the software, the centroid position is calculated (to 1/100th of a pixel normally). Let this be 0.2 sec.
Please download the pdf: www.astronomy.hu/guide1.pdf