Very long exposures requiring precise tracking needed for imaging deep-sky objects may now be achieved through an advanced imaging technique called autoguiding. This article provides a brief introduction and how one could construct a do-it-yourself guider that delivers equally satisfying results for a fraction of the cost of ultra expensive commercially available counterpart.
Guided imaging simply involves active monitoring of the telescope’s tracking accuracy by observing a reference object (any bright star) and making the necessary adjustments to nudge the telescope to the east or to the west so that the reference object remains stationary for the whole duration of an exposure. The simplest example is a setup involving an imaging telescope with (equipped with a finderscope) on a tracking mount. After the object to be imaged has been properly framed and focused, the imager adjusts the finderscope and centers its cross hair to the brightest star in its field. This bright star now serves as the reference object called the guide star and the finderscope now performs the task of a guidescope. The idea is that, for as long as the guidescope’s crosshair is centered on the guidestar, the imager knows that the telescope is tracking properly. To achieve better sensitivity to drift, more powerful dedicated guidescopes may be used.