The aberration measurement program has been developed for improving the optical quality of ground-based telescopes.
This program is based on the Curvature Sensing Technique (CST) and aberrations are estimated from two defocused
stellar images. We used iterative algorithm that simulates closed-loop wave-front compensation in optics. It has been
applied to the telescope of Bohyunsan Optical Astronomy Observatory (BOAO) in Korea. The most frequently
encountered aberration by misalignment was coma. As a result, the image quality of telescope was improved after
adjustment the alignment of secondary mirror.