الفهرس 
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Abstract
Research Objective
The aim of this thesis is to develop an automatic focus system for
KAO. The automatic focus system nds the best focus by moving
the CCD imaging system and measures the image focus level by
using a focus measure operator. The focus measure operator is used
to determine the focus levels of a sequence of images. The images
are acquired at a varying distance between a camera lens and a
scene object. The proper focus measure operator is chosen based on
a performance comparison of several measures applied to observed
astronomical images.
1.4.1 Refracting Telescope
A Refracting telescope is an optical telescope that uses a lens as
its objective to form an image. It got its name from the fact that
its image is formed by bending of light (refraction). A refractor
can be a combination of a convex lens and a concave lens or a
combination of two convex lenses [4]. One of the main defects of
the Refracting telescope is the aberration e ects. That is because
the light of di erent wavelengths passing through a lens is bent or
`refracted’ unequally due to the di erence in refractive index for
di erent light wavelengths. Another defect of refracting telescope
is the size limitation due to large diculties in constructing large
lenses. So, in the most research purposes, the Refracting telescope