| 摘要 |
PROBLEM TO BE SOLVED: To provide an imaging optical system which is miniaturized, has high resolution and suppresses an increase of manufacture cost.SOLUTION: The imaging optical system comprises, sequentially from the object side, a first lens 101 having a positive power, a second lens 102 which is a meniscus lens having a convex surface on the image side, a third lens 103 having a positive power, and a fourth lens 104 having a negative power. A surface of the third lens on the image side has a positive power in the paraxial area, and has a negative power in the peripheral area. A surface of the fourth lens on the image side has a negative power in the paraxial area, and has a positive power in the peripheral area. The first lens is provided with diffraction gratings on the image side surface. If it is assumed that the focal length of the second lens is f, the composite focal length of the imaging optical system is f, and the distance between the aperture stop or the apex of the object side surface of the first lens, whichever is closer to the object side, and the image surface is TTL, the imaging optical system satisfies following expressions (1) and (2). |
