In order to satisfy the remote detection requirements for the surface defects on the cables of cable stayed bridges, an opto- mechanical system of a high definition video telephoto objective is designed and manufactured. According to the objective definition requirement of 4 mm at the distance of 300 m, the imaging definition of 234 cycle/mm with a focal length of 320 mm is determined. A proper initial configuration is chosen, and then some optimization procedures are carried out with the optics design program OSLO, including the focus zooming, glass exchanging, lens reduction, etc. Finally an optical configuration of the telephoto objective is obtained with the relative aperture of 1/5.7, the field angle of 2 ω =1.379°, and the definition of 250 cycle/mm. The opto- mechanical structures are designed rationally and the experimental objective is manufactured. The definition testifies that its actual objective definition reaches 4 mm at the distance of 300 m. The site imaging experiment results at the location of a cable stayed bridge show that this system satisfies the remote detection requirements for the surface defects on the real engineering structures.