A new optical system with a fairly large field of view and excellent image quality can be designed by making both the surfaces of primary and secondary mirrors in the Cassegrain system spherical

adding two or more correcting lenses in front of the focal plane

and adding a 4

th

order term to one surface of the parallel plates as a hermetically sealed chamber. The aspheric surface of the plate with 4

th

order term is concave

and it can be made spherical by grinding it with hinge support around and equal loads applied

and after the equal loads being released

the surface springs back to form the desired aspherical surface with 4

th

order term. So

from the viewpoint of optical technology

this system has spheres and planes only. Four systems with relative apertures of

F

/3

F

/5

F

/8 and

F

/10 have been designed with the same effective diameter and field of view: φ=300 mm and 2 ω=1°

and the image quality is close to or reaches the diffraction limit.