Image pickup optical system and image pickup apparatus using the same
An image pickup optical system includes in order from an object side, a first lens having a positive refractive power, a second lens having a negative refractive power, a third lens having a positive refractive power, a fourth lens having a positive refractive power, and a fifth lens having a negative refractive power. An aperture stop is disposed nearest to the object side, and the first lens has a biconvex shape. An image-side surface of the third lens has in a peripheral portion, an area of which, a refractive power becomes weaker as compared to a refractive power of a central portion thereof. An object-side optical function surface of the fourth lens has a concave shape, and an object-side surface of the fifth lens has a concave shape.
1. An image pickup optical system comprising in order from an object side:
a first lens having a positive refractive power;
a second lens having a negative refractive power;
a third lens having a positive refractive power;
a fourth lens having a positive refractive power; and
a fifth lens having a negative refractive power, wherein
the fourth lens is a meniscus lens having a convex surface directed toward an image side, and
an aperture stop is disposed nearest to the object side, and
the following conditional expressions are satisfied:
0.5 <TL /(2 ×IH )<1.5, and
0.4 <Σd L /f <0.55,
where,
TL denotes an overall length of the image pickup optical system,
IH denotes an image height,
Σd L denotes a total thickness of lenses of the image pickup optical system, and
f denotes a focal length of the image pickup optical system.
2. The image pickup optical system according to claim 1 , wherein the following conditional expression is satisfied:
1.5 <f 3 /f< 2.5
where,
f 3 denotes a focal length of the third lens, and
f denotes a focal length of the overall image pickup optical system.
3. The image pickup optical system according to claim 1 , wherein a shape of the third lens is a meniscus shape having a convex surface directed toward the object side.
4. The image pickup optical system according to claim 1 , wherein an image-side surface of the third lens has a shape such that a concave surface is directed toward an image side, near an optical axis, and a shape such that a convex surface is directed toward the image side, at a peripheral portion.
5. The image pickup optical system according to claim 1 , wherein the following conditional expression is satisfied:
2.0 <r 7 /f< 3.0
where,
r 7 denotes a paraxial radius of curvature of an image-side surface of the third lens, and
f denotes a focal length of the overall image pickup optical system.
6. The image pickup optical system according to claim 1 , wherein the following conditional expression is satisfied:
0.05<( r 10 +r 11 )/( r 10 −r 11 )<0.6
where,
r 10 denotes a paraxial radius of curvature of an object-side surface of the fifth lens, and
r 11 denotes a paraxial radius of an image-side surface of the fifth lens.
7. The image pickup optical system according to claim 1 , wherein the aperture stop is positioned at an image side of an object-side vertex of the first lens.
8. The image pickup optical system according to claim 1 , wherein each of the first lens, the second lens, the third lens, the fourth lens, and the fifth lens are formed of a resin.
9. An image pickup apparatus comprising:
an image pickup optical system according to claim 1 ; and
an image pickup element.
10. The image pickup apparatus according to claim 9 , wherein the image pickup optical system and the image pickup element are integrated.
11. The image pickup apparatus according to claim 9 , wherein the image pickup optical system is integrated with an auto-focus mechanism.