Lens system and optical device having the same
A lens system has a plurality of lenses, a stop, and a diffractive surface, the entire lens system moves during focusing, and the lens system satisfies the condition of β≧0.5, where β is a maximum photographic magnification.
1. An imaging lens system for imaging an object onto image taking means, the imaging lens system comprising:
a plurality of lenses and a stop, wherein a diffractive surface is present in the imaging lens system,
the imaging lens system moving the whole or part of the imaging lens system during focusing for a distance to an object from an infinity side to a near side and satisfying the following conditions:
|β|≧0.5,
|Δ S/f|≧ 1.0,
where β is a maximum imaging magnification, ΔS is a maximum moving distance of the whole or part of the imaging lens system during focusing from an object at infinity to an object at a near distance, and f is a focal length of the entire imaging lens system.
2. The imaging lens system according to claim 1 , wherein said plurality of lenses are arranged symmetric or substantially symmetric with respect to said stop.
3. The lens system according to claim 1 , wherein said diffractive surface consists of a diffraction grating rotationally symmetric with respect to the optical axis,
wherein when the phase φ(h) of said diffraction grating is given by the following equation:
φ( h )=(2π/λ)*( C 1 * h 2 + C 2 * h 4 + C 3 * h 6 + . . . + Ci*h 2 i ),
where λ is an arbitrary wavelength in the visible region, Ci aspheric phase coefficients, and h a height from the optical axis,
the following conditions are satisfied:
C 1 <0 and C 2 >0.
4. An optical device comprising:
said lens system of claim 1 ; and
a housing which holds said lens system.
5. The imaging lens system according to claim 1 , wherein a lens of the plurality of lenses has the diffractive surface.
6. An imaging lens system for imaging an object onto image taking means, the imaging lens system comprising:
from an object side to an image side, two optical elements having positive optical powers, an optical element having negative optical power, a stop, an optical element having negative optical power, and two optical elements having positive optical powers, wherein an optical surface of an optical element of the aforementioned six optical elements is a diffractive surface,
the imaging lens system moving the whole or part of the imaging lens system during focusing for a distance to an object from an infinity side to a near side and satisfying the following condition:
|β|≧0.5,
where β is a maximum imaging magnification.