Lens system and optical device having the same

• US 6,924,949 B2
• Filed: 05/10/2001
• Issued: 08/02/2005
• Est. Priority Date: 05/12/2000
• Status: Expired due to Fees

• Current Assignee: Canon Kabushiki Kaisha (Canon Inc.)
• Original Assignee: Canon Kabushiki Kaisha (Canon Inc.)
• Inventors: Harada, Akira
• Primary Examiner(s): SCHWARTZ, JORDAN MARC
• Application Number:
  US09/851,937
• Publication Number:
  US 20020041451A1
• Time in Patent Office: 1,545 Days
• Field of Search: 359739-741, 359/558, 359754-756, 359/763, 359/771, 359/784, 359/793, 359/757, 359/758, 359/759, 359/760
• US Class Current: 359/760
• CPC Class Codes: G02B 13/003 having two lenses
• CPC Class Codes: G02B 13/0045 having five or more lenses
• CPC Class Codes: G02B 13/0055 employing a special optical element
• CPC Class Codes: G02B 13/006 at least one element being a compound optical element, e.g. cemented elements
• CPC Class Codes: G02B 27/42 Diffraction optics , i.e. systems including a diffractive element being designed for providing a diffractive effectG02B27/60 takes precedence
• CPC Class Codes: G02B 27/4211 correcting chromatic aberrations G02B27/0056, G02B27/4222, G02B27/4227 take precedence
• CPC Class Codes: G02B 27/4288 having uniform diffraction efficiency over a large spectral bandwidth
• CPC Class Codes: G02B 5/1895 such optical elements having dioptric power
• CPC Class Codes: G02B 9/08 arranged about a stop

Abstract

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.

Claims

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, Δ

S 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

)*(C1*h2+C2*h4+C3*h6+ . . . +Ci*h2i),

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;

C1<

0 and C2>

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.