Lens system and optical device having the same

• US 7,133,221 B2
• Filed: 09/15/2005
• Issued: 11/07/2006
• 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, Akria
• Primary Examiner(s): SCHWARTZ, JORDAN MARC
• Application Number:
  US11/226,329
• Publication Number:
  US 20060077569A1
• Time in Patent Office: 418 Days
• Field of Search: 359/773, 359/785
• US Class Current: 359/785
• 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 comprising;

a diffractive surface, and

a first lens unit of a positive optical power, a second lens unit of a negative optical power disposed on the image side of said first lens unit, and a third lens unit of a positive optical power disposed on the image side of said second lens unit,

wherein during focusing from an object at infinity to an object at a near distance, said first lens unit is fixed, said second lens unit moves toward an image side, and said third lens unit moves toward the object side,

wherein the following condition is satisfied by said lens system;

|β

|≧

0.5,

where β

is a maximum imaging magnification, and wherein said first lens unit comprises a positive lens closest to the object.

2. The imaging lens system according to claim 1, which satisfies the following condition:

0.50<

Δ

s2/|Δ

s3|<

1.50,

where Δ

s2 is a moving distance of said second lens unit during the focusing and Δ

s3 is a moving distance of said third lens unit during the focusing.

3. The imaging 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. The imaging lens system according to claim 1, wherein a stop is placed between said second lens unit and said third lens unit and said stop is fixed during the focusing.

5. The imaging lens system according to claim 1, which comprises a flare cut stop in the optical path.

6. The imaging lens system according to claim 1, wherein said second lens unit and said third lens unit both comprise respective cemented lenses.

7. The imaging lens system according to claim 1, further comprising a fourth lens unit of a negative optical power disposed on the image side of said third lens unit.

8. An optical device comprising:

the imaging lens system of claim 1; and

a housing which holds said imaging lens system.