Imaging optical system and imaging device including imaging optical system comprising seven lenses of −−−++−+ refractive powers
A wide-angle imaging optical system obtains sufficient information in the image periphery, and achieves high-performance imaging across the entire field of view. The imaging optical system uses stereographic projection, and includes, in sequence from an object, a first lens with a negative refractive power having a convex surface facing the object, a second lens with a negative refractive power, a third lens with a negative refractive power, a fourth lens with a positive refractive power, an aperture stop, a fifth lens with a positive refractive power, a sixth lens with a negative refractive power, and a seventh lens with a positive refractive power.
1. An imaging optical system using stereographic projection with a field of view exceeding 180 degrees, the system comprising, in sequence from an object:
a first lens with a negative refractive power having a convex surface facing the object;
a second lens with a negative refractive power;
a third lens with a negative refractive power;
a fourth lens with a positive refractive power;
an aperture stop;
a fifth lens with a positive refractive power;
a sixth lens with a negative refractive power; and
a seventh lens with a positive refractive power,
wherein the imaging optical system satisfies the conditional expressions:
−23< f 1/ f<− 12 (1)
−8< f 2/ f<− 5 (2)
2.5< f 5/ f< 4.5 (3)
−3.0< f 6/ f<− 1.9 (4)
where f is a focal length of the entire imaging optical system,
f1 is a focal length of the first lens,
f2 is a focal length of the second lens,
f5 is a focal length of the fifth lens, and
f6 is a focal length of the sixth lens.
2. The imaging optical system according to claim 1 satisfying the conditional expression:
−0.02< n 6 −n 5<0.16 (5)
where n5 is a refractive index of the fifth lens for a d-line, and
n6 is a refractive index of the sixth lens for the d-line.
3. The imaging optical system according to claim 1 , satisfying the conditional expression:
2.4< f 7/ f< 3.0 (6)
where f7 is a focal length of the seventh lens.
4. The imaging optical system according to claim 1 , wherein
the second lens includes a concave surface facing the object.
5. The imaging optical system according to claim 1 , wherein
the fifth lens comprises optical glass.
6. An imaging device, comprising:
the imaging optical system according to claim 1 ; and
a solid-state image sensor.