Imaging optical system with focusing function
An imaging optical system is provided and has a focusing section including a cemented lens (first and second lenses), which includes first and second fluid materials having different refractive indices from each other; and whose cemented surface shape can be electrically controlled. A refractive index Nd 1 of the first fluid material, a refractive index Nd 2 of the second fluid material, a minimum value RA of a radius of curvature of the cemented surface of the cemented lens, a focal length fa of the whole cemented lens, and a focal length f of the whole lens system satisfy the conditions specified in the specification.
1. An imaging optical system having a focus function, which comprises a lens system, the lens system comprising:
a lens group remaining fixed during focusing;
a focusing cemented lens including a first fluid material and a second fluid material as lens materials in this order from an object, wherein the first and second fluid materials have different refractive indices, and a shape of an interface between the first and second fluid materials is variable; and
a control unit that electrically controls the shape of the interface between the first and second fluid materials, depending on a distance from the object,
wherein the focusing cemented lens has a power as a whole and satisfies conditions (1) to (3) over an entire focusing region:
0.1 <|Nd 1- Nd 2|<0.5 (1)
3 <|RA|/f <20 (2)
| fa/f |>1.0, and, (3)
wherein
Nd 1 represents a refractive index to a d line of the first fluid material,
Nd 2 represents a refractive index to a d line of the second fluid material,
RA represents a minimum value in use of a radius of curvature of the interface between the first and second fluid materials,
fa represents a focal length of the focusing cemented lens, and
f represents a focal length of the lens system.