| 摘要 |
An image pickup optical system having four lenses includes in order from an object side, a first lens having a biconvex shape, and a positive refractive power, a second lens having a biconcave shape, and a negative refractive power, a third lens having a meniscus shape with a concave surface thereof directed toward the object side, and a positive refractive power, and a fourth lens having a biconcave shape, and a negative refractive power, and a diaphragm is disposed nearest to the object side, and the surface on the object side of the fourth lens does not have a point of inflection as well as the optical system satisfying the recited numerical conditions. |
| 主权项 |
1. An image pickup optical system having four lenses, comprising in order from an object side:
a first lens having a biconvex shape, and a positive refractive power; a second lens having a biconcave shape, and a negative refractive power; a third lens having a meniscus shape with a concave surface thereof directed toward the object side, and a positive refractive power; and a fourth lens having a biconcave shape, and a negative refractive power, wherein a diaphragm is disposed nearest to the object side, and the image pickup optical system satisfies the following conditional expressions
−0.9<f4/f<0 (1)−0.04<(r8+r9)/(r8−r9)<0.9 (2)−0.03<(r4+r5)/(r4−r5)<0.55 (4) where, f4 denotes a focal length at a near-axis of the fourth lens, f denotes a focal length of the overall image pickup optical system, r8 denotes a radius of curvature of a surface on the object side of the fourth lens, and r9 denotes a radius of curvature of a surface on an image side of the fourth lens, r4 denotes a radius of curvature of a surface on the object side of the second lens, r5 denotes a radius of curvature of a surface on the image side of the second lens, andwherein
the surface on the object side of the fourth lens does not have a point of inflection. |
