Glossary

Guiding with ST-4

updated: 2025-12-03


If you are planning to capture longer exposures with your DSLM of CMOS camera you will need some kind of autoguider that keeps your target and automatically corrects small pointing errors deriving (e.g. periodic errors) from your equipment or atmospheric turbulences.


Autoguiding typically requires an additional camera fixed to your guider scope. This camera will lock on a star and with help of some electronics (like ASIAIR Pro) or a computer program (like ) will constantly calculate tracking correction steps that it sends to your mount (via an ST-4 interface) to compensate for the error. 


  • Connect the ST-4 port of the guide camera with the ST-4 port of the mount.
  • Connect the USB port at the camera with a computer
  • use a programm like PHD2 (freeware) to select a guide star and let the mount do the guiding.
  • On  select "On-Camera" as mount
  • on ASIAIR Pro select "On-Camera-ST4" as mount

Disadvantages of ST-4 Guiding

  • With ST-4 you have to calibrate near your target. The pole area is not a good/easy place to calibrate.
  • If you are using ST-4, you need to recalibrate on each target, as ST-4 cannot transmit the current declination from the mount to the pier, nor which side of the pier it is on, as compared to the ASCOM protocol.  ASCOM allows you to reuse a calibration, eliminating the need to recalibrate for each target. Additionally, it automatically adjusts after a meridian flip.
  • No GoTo function will be provided by any tools, you'll have to use the hand controller of your mount to move the telescope into the right direction
  • No Dithering
  • The ST-4 is only intended for guiding, nothing else will be available


Autoguider Configurations (pictures by courtesy of Astroshop)


Configuration

Specifics

Schema

Pro's and Con's

Computer based guiding

Using a guide scope

  • more weight (guide scope and laptop)
  • high power consumption
  • extra guide scope required
  • very flexible solution

Using a Off-Axis-Guider

  • high power consumption
  • more weight (laptop)
  • small aperture reduction
  • very flexible solution

Stand-Alone Guide

Using a guide scope

  • more weight (guide scope)
  • small aperture reduction
  • very flexible solution
  • lowest weight
  • low power consumption

Using a Off-Axis-Guider

best suited for Maksutov or Schmidt-Cassegrain telescopes:

  • small aperture reduction
  • very flexible solution
  • lowest weight
  • low power consumption




Here are links to some good articles about autoguiding:


Created with the Personal Edition of HelpNDoc: Make Your PDFs More Secure with Encryption and Password Protection