The invention discloses an
endoscope optical
system which is composed of a first lens, a steering
prism, a diaphragm, a second lens, a third lens, a fourth lens, a fifth lens, a sixth lens, a seventh lens and a
beam splitter prism from an object plane to an
image plane, the focal power of the first lens is negative, the object side is a convex surface, and the image side is a
concave surface; the focal power of the second lens is positive, the object side is a plane, and the image side is a convex surface; the object side of the third lens is a convex surface, the focal power of the fourth lens is opposite to that of the third lens, and the image side is a convex surface; the focal power of the fifth lens is positive, and the image side of the fifth lens is a convex surface; the focal power of the sixth lens is negative, the object side is a
concave surface, and the image side is a
concave surface; the focal power of the seventh lens is positive, the object side is a convex surface, and the image side is a convex surface; the object space
numerical aperture NA of the
endoscope optical
system is more than 0.001 and less than 0.006, and the
endoscope optical
system has the advantages that lens combinations with different surface shapes and focal powers are used, and the
depth of field and the axial resolution capability of an endoscope are improved by reducing the object space
numerical aperture.