PURPOSE: To realize a large aperture, a compact size and a wide angle respectively, by giving the conditions to the parameter of a lens system of 4 groups and 6 lenses.

CONSTITUTION: The lens system includes the 1st concave meniscus lens 1, a cemented lens of the 2nd concave meniscus lens 2 (focal distance f2) and the 3rd convex meniscus lens 3 (refractive index u3), a cemented lens of the 4th diaphragm convex meniscus lens 4 (u4) and the 5th concave meniscus lens 5 (f5), and the 6th concave meniscus lens 6 (f8) respectively. Then the conditions (1)W (5) are satisfied when the composite focal distance is set to (f). In such way, a wide-angle lens type of a combination of a concave-convex-concave lenses which is used for a photographing lens, etc. is used to obtain the best performance at about 1X magnification ratio.