| 摘要 |
Provided is an optical system whereby the amount of non-effective light (i.e. light beyond the maximum field of view) converging on the focal point of an object-side-most lens group having positive optical power is reduced, making it possible to reduce heating of a member near said focal point, prevent deformation and degradation of said member, and reduce the impact on imaging performance. Said optical system has the following: an object-side-most first lens group (G1), which has positive optical power; a diaphragm member (ST) disposed on the image side of the first lens group (G1); and a second lens group (G2) disposed on the image side of the diaphragm member (ST). This optical system satisfies the relations 0.20 < ds/f1 < 0.60 and 1.00×&phgr;2 < &phgr;s < 0.8×&phgr;1 (in mm), with ds representing the distance along the optical axis between the surface of the image-side-most lens of the first lens group (G1) and the diaphragm member (ST), f1 representing the focal length of the first lens group (G1), &phgr;2 representing the outer diameter of the object-side-most lens of the second lens group (G2), and &phgr;s representing the aperture diameter of the diaphragm member (ST). |
