To provide an imaging optical system which excels in imaging performance and is compact.
The imaging optical system comprises, in order from an object side, an aperture stop S, a first lens L1, a second lens L2, a third lens L3 and a fourth lens L4. The first lens is a biconvex lens, the second lens is a negative lens having a strong concave surface on an image side, the third lens is a positive lens having a strong convex surface on the image side, and the fourth lens is a negative lens having a strong concave surface on the object side, and they satisfy expression A: -0.9(r2+r3)/(r2-r3)-0.08, expression (2): 0.011/2-1/10.03, expression (4):-2f/r60.01, expression (9): 0.08d7/f0.4 and expression (6): 0f/r91. In expressions, f means a focal length of an entire system, 1 and 2 mean Abbe numbers of the first lens and the second lens respectively, r2 and r3 mean radii of curvature on the object side and the image side of the first lens respectively, r6 means the radius of curvature on the object side of the third lens, r9 means the radius of curvature on the image side of the fourth lens, and d7 means a distance on an optical axis between the third lens and the fourth lens.
UCHIDA YOSHIHIRO
GOTO HISASHI
| JP2007212877A | 2007-08-23 | |||
| JP2008185880A | 2008-08-14 |
Masayuki Fujinaka
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