ABSTRACT
This chapter discusses the importance of accurate focusing, as well as the need for good mechanical robustness in the focus mechanism. It shows that any conventional astrophotography optic is fitted with a motorized focuser and that conventional shorter focal-length photographic optics is focused by hand. The adjustment that minimizes a measured star width can be performed automatically. Maxim DL has autofocus capabilities that use the approximate focus position and then measure the half flux density values for a series of evenly stepped focus positions on either side. Focusing is one of those things that require constant monitoring. In addition to manual intervention there are a number of options, depending on the image capture software. Mechanical backlash is a further issue to contend with during automated focusing and is a potential gotcha. It is fairly obvious that gear-based rack and pinion focuser mechanisms have mechanical play but when motorized, both they and Crayford-based autofocus systems are affected.
