A special kind of long focal-length optical system using annular aperture which is expected to be used in space cameras optical imaging system is introduced,it can also considered as a kind of sparse aperture system. Light enters the optical system through an outer annular aperture and is focused by a series of concentric annular reflectors and compensation lens to the image plane. They have large obscuration ratio. They have compactness and good image quality,which is expected to be used in micro satellite payload with high resolution. The result of a long focal length optics with six-fold reflection is introduced. Their performance evaluation and tolerance analysis are given and compared.