Autoguider

Introduction

Without a doubt, one of the greatest technological achievements in the field of astrophotography has been the development of the autoguider. In the not too distant past, many an astrophotographer was forced to stare into a guiding eyepiece on their telescope and manually make corrections to the tracking of their mount for the entirety of each and every exposure. For each exposure, the photographer would monitor a guide star in the guiding eyepiece, and when the star drifted off the cross hairs, the photographer would manually adjust the mount to correct for this error. This would continue nonstop throughout the entire exposure, and depending on the position of the telescope, this could force the photographer to sit or lie in a position that would make a professional contortionist cringe. Luckily, the autoguider came along and provided a solution to this misery. now an astrophotographer can automate the image taking process and catch up on that much needed catnap while the exposures click away.

What is an Autoguider?

The autoguider is basically a computer controlled system which uses a CCD imaging device to constantly make short exposures of a small section of sky, typically through a guidescope which is pointed in the same area as the object one is photographing. Each exposure is stored in memory and the computer calculates the position of one of more stars. In each subsequent exposure, the movement of the guide star is monitored by the computer, and its error (movement) from the original baseline exposure is calculated. From this error, the computer then calculates the necessary corrections that would be required at the mount to bring the guide star back to its original position. These corrections are finally sent to the mount, and the error is corrected. This process repeats continually for the entire entirety of the exposure and photographic session.

Several types of autoguiders are commonly used in astrophotography today. The godfather of all autoguiders is the Santa Barbara Instruments Group (SBIG) ST-4. It is a self-contained unit and does not require a separate computer (laptop) to operate. Its successor is the highly successful STV which improves the ST-4 design by incorporating many additional features, including full automation of the calibration and tracking process, as well as providing a large 5" LCD display which is used to display images of the actual guide star as well as a plethora of other useful graphs and functions. Finally, there are the webcam based autoguiding systems. These autoguiders utilize inexpensive webcams as the imaging element, and programs such as Guidedog (freeware) to perform the autoguiding function. However, they do require an external computer (laptop) and are not nearly as sensitive as the ST-4 and STV self-contained autoguider systems.

SBIG STV

SBIG STV Autoguider system with CCD head

I originally started out with a webcam based autoguider, but after having to replace the webcam I was using, the Celestron Neximage, twice due to failures, I got fed up and invested in a used SBIG STV autoguiding system which I purchased through Astromart. Plus, I was getting fed up with having to lug my laptop out everytime I wanted to image. The STV is an incredible piece of equipment and is extremely simple to use. Proper orientation of the CCD in the guidescope is not required as in older autoguiders such as the ST-4, and only a few buttons are required to calibrate the mount and begin automated tracking as the entire process is fully automated. Finally, the STV can be used for a range of other functions including imaging and polar drift alignment.