| 摘要 |
<p>PROBLEM TO BE SOLVED: To provide an optical system which has a long back focus, a compact system size, and a wide view angle and yet easily provides high quality images over an entire screen area.SOLUTION: The optical system comprises, in order from the object side to the image side, a first lens group having negative refractive power, an aperture stop, and a second lens group having positive refractive power, where the second lens group has a lens G21 having positive refractive power on the most object side. A focal length f21 of the lens G21, a focal length f2 of the second lens group, a curvature radius R21a of an object-side surface of the lens G21, and a curvature radius R21b of an image-side surface of the lens G21 are each set appropriately.</p> |
