Reflecting objective system

A reflecting objective system that excludes a refracting optical element and receives light from an object separate from the system with a given distance therebetween and acts to form an image of the object, comprising, in the travelling order of light incident from the object side:

• a first reflecting mirror having a positive optical power,
• a second reflecting mirror and a third reflecting mirror at least one of which has a positive optical power, and
• a fourth reflecting mirror having a positive optical power,
• each reflecting mirror having different reflecting surfaces than the other reflecting mirrors,
• a light beam from said object being reflected from the mirrors in the order of first, second, third and fourth reflecting mirrors without the beam intersecting an optical axis of the system,
• wherein total optical power of said first, second and third reflecting mirrors has a positive value, and
• at least one of the reflecting surfaces of said first reflecting mirror and said fourth reflecting mirror being as aspherical surface,
• an absolute value of powers of said second and third reflecting mirrors being smaller than an absolute value of powers of said first and fourth reflecting mirrors,
• said third reflecting mirror being disposed between said first reflecting mirror and said second reflecting mirror, and
• said reflecting objective system satisfying the condition (12):
• 0. 01.ltoreq..vertline..DELTA.M.sub.13 .vertline..multidot.(f/L.sub.01.sup.2).ltoreq.0.1 (12)
• wherein the reference symbol .DELTA.M.sub.13 represents a mechanical distance between said first reflecting mirror and said third reflecting mirror, f is the focal length of the reflecting objective system, and the reference symbol L.sub.01 represents a distance between said object and said first reflecting mirror.