Wide-aperture spherical primary mirror off-axis afocal optical system

A wide-aperture spherical primary mirror off-axis afocal optical system comprising:

• a primary mirror and a secondary mirror, the primary mirror being a spherical reflector, the secondary mirror being a higher-order aspherical reflector, the primary mirror and the secondary mirror forming an off-axis two-mirror system to compress a beam aperture;
• and
• an aberration compensation mirror group, the aberration compensation mirror group being a coaxial reflective system that is used off-axis, the aberration compensation mirror group having focal power to produce compensation aberrations;
• wherein an incident beam passes through and is reflected by the primary mirror and the secondary mirror sequentially and enters the aberration compensation mirror group thereafter,
• wherein the aberration compensation mirror group includes a first lens, a second lens and a third lens that are sequentially arranged, a distance from a front surface of the first lens to a rear surface of the third lens is T, the focal length of the aberration compensation mirror group is f2 and they satisfy a relational expression of:
• 0.7≤f2/T≤1.2;
• wherein a focal length of the first lens is f21, a curvature radius of a front surface of the first lens is R3, a curvature radius at a center of a rear surface of the first lens is R4, an on-axis thickness of the first lens is d3, a distance from a front surface of the first lens to a rear surface of the third lens is T, and they satisfy relational expressions of:
• −1.85f21/f2−1.75
• 1.13(R3+R4)/(R3−R4)1.45
• 0.09d3/T0.11;
• wherein a focal length of the second lens is f22, a curvature radius of the front surface of the second lens is R5, a curvature radius of a rear surface of the second lens is R6, an on-axis thickness of the second lens is d5, a distance from a front surface of the first lens to a rear surface of the third lens is T, and they satisfy relational expressions of:
• −3.2f22/f2−1.15
• −1(R5+R6)/(R5−R6)0.3
• 0.072d5/T0.074;
• wherein a focal length of the third lens is f23, a curvature radius of a front surface of the third lens is R7, a curvature radius of a rear surface of the third lens is R8, an on-axis thickness of the third lens is d7, a distance from a front surface of the first lens to a rear surface of the third lens is T, and they satisfy relational expressions of:
• 1.57≤f23/f2≤1.63
• 0.41≤(R7+R8)/(R7−R8)≤0.90
• 0.13≤d7/T≤0.18.