  Focus accuracy affects the quality of the astronomical observations.
Auto-focusing is necessary for imaging systems designed for astronomical
observations. The automatic focus system searches for the best focus position
by using a proposed search algorithm. The search algorithm uses the image's
focus levels as its objective function in the search process. This paper aims
to study the performance of several search algorithms to select a suitable one.
The proper search algorithm will be used to develop an automatic focus system
for Kottamia Astronomical Observatory (KAO). The optimal search algorithm is
selected by applying several search algorithms into five sequences of
star-clusters observations. Then, their performance is evaluated based on two
criteria, which are accuracy and number of steps. The experimental results show
that the Binary search is the optimal search algorithm.
