Zoom lens, and camera incorporating such zoom lens

• US 20030175021A1
• Filed: 01/24/2003
• Published: 09/18/2003
• Est. Priority Date: 01/25/2002
• Status: Active Grant

• Current Assignee: Canon Kabushiki Kaisha (Canon Inc.)
• Original Assignee: Canon Kabushiki Kaisha (Canon Inc.)
• Inventors: Hamano, Hiroyuki
• Granted Patent: US 6,763,186 B2
• Time in Patent Office: Days
• US Class Current: 396/72
• CPC Class Codes: G02B 15/144105 arranged +-+-
• CPC Class Codes: G02B 15/144113 arranged +-++
• CPC Class Codes: G02B 15/145121 arranged +-+-+
• CPC Class Codes: G02B 15/173 arranged +-+

Abstract

Disclosed is a zoom lens system which uses a diffractive optical element such that high optical performance can be obtained over the overall power variation range. The zoom lens system includes a first lens unit having positive optical power, and a second lens unit having negative optical power and disposed on a rearward side of the first lens unit. A diffractive optical portion is provided on a cemented surface, which is convex toward a forward side, in the first lens unit or the second lens unit.

Claims

1. A zoom lens system comprising:

a first lens unit having positive optical power, said first lens unit being not moved for zooming; and

a second lens unit having negative optical power, said second lens unit being disposed on a rearward side of said first lens unit, and being moved for zooming;

wherein said first lens unit has a cemented surface convex toward a forward side, and a diffractive optical portion is provided on said cemented surface.

2. A zoom lens system according to claim 1, wherein said zoom lens forms an image on an opto-electric converting element.

21. A camera comprising:

a zoom lens system recited in claim 1;

and

an opto-electric converting element for receiving an image formed by said zoom lens system.

3. A zoom lens system comprising:

a first lens unit having positive optical power; and

a second lens unit having negative optical power, said second lens unit being disposed on a rearward side of said first lens unit, and being moved for zooming;

wherein said first lens unit has a cemented surface convex toward a forward side, a diffractive optical portion is provided on said cemented surface, and a following condition is satisfied,

0.5<

RD/f1<

1.2

where RD is the radius of curvature of said cemented surface, and f1 is the focal length of said first lens unit.

4. A zoom lens system according to claim 3, wherein a following condition is satisfied,

0.01<

C₂·

(ft/Fnot)<

0

where λ

d is the wavelength of d-line, h is the distance from an optical axis, C_2i is the phase coefficient, the phase given to a wave front by said diffractive optical portion is represented by a follows formula,

φ

(h)=(2π

/λ

d)·

(C₂·

h²+C₄·

h⁴+ . . . +C_2i·

h²ⁱ)

ft is the focal length of an entire system at telephoto end, and Fnot is the F-number at telephoto end.

5. A zoom lens system according to claim 3, further comprising a third lens unit disposed on a rearward side of said second lens unit, said third lens unit being not moved for zooming.

6. A zoom lens system according to claim 3, further comprising a third lens unit disposed on a rearward side of said second lens unit, said third lens unit being not moved for zooming;

and a fourth lens unit having positive optical power, said fourth lens unit being disposed on a rearward side of said third lens unit, and being moved for zooming.

7. A zoom lens system according to claim 3, further comprising a third lens unit disposed on a rearward side of said second lens unit, said third lens unit being not moved for zooming;

and a fourth lens unit having negative optical power, said fourth lens unit being disposed on a rearward side of said third lens unit, and being moved for zooming.

8. A zoom lens system according to claim 3, further comprising a third lens unit disposed on a rearward side of said second lens unit, said third lens unit being not moved for zooming;

a fourth lens unit having negative optical power, said fourth lens unit being disposed on a rearward side of said third lens unit, and being moved for zooming; and

a fifth lens unit having positive optical power, said fifth lens unit being disposed on a rearward side of said fourth lens unit.

9. A zoom lens system according to claim 3, wherein a following condition is satisfied,

1.3<

|f1/(fw·

ft)^1/2|<

4.0

where f1 is the focal length of said first lens unit, and fw and ft are focal lengths of an entire system at wide-angle end and telephoto end, respectively.

10. A zoom lens system according to claim 3, further comprising a third lens unit disposed on a rearward side of said second lens unit, said third lens unit being not moved for zooming, and being moved for stabilizing an image;

and a lens component disposed on a rearward side of said third lens unit, said lens component including at least one lens unit movable for zooming; and

wherein a following condition is satisfied,

0.5<

|(1−

β

3)·

β

r|<

3

where β

3 is the magnification of said third lens unit at telephoto end for infinity object, and β

r is the magnification of said lens component at telephoto end for infinity object.

11. A zoom lens system according to claim 3, wherein said zoom lens forms an image on an opto-electric converting element.

22. A camera comprising:

a zoom lens system recited in claim 3;

and

an opto-electric converting element for receiving an image formed by said zoom lens system.

12. A zoom lens system comprising:

a first lens unit having positive optical power; and

a second lens unit having negative optical power, said second lens unit being disposed on a rearward side of said first lens unit, and being moved for zooming;

wherein said second lens unit has a cemented surface convex toward a forward side, and a diffractive optical portion is provided on said cemented surface.

13. A zoom lens system according to claim 12, wherein a following condition is satisfied,

−

2.8<

RD/f2<

−

1.2

where RD is the radius of curvature of said cemented surface, and f2 is the focal length of said second lens unit.

14. A zoom lens system according to claim 12, wherein a following condition is satisfied,

−

0.05<

(C₂·

H²+C₄·

H⁴)/f2<

−

0.0007

where λ

d is the wavelength of d-line, h is the distance from an optical axis, C_2i is the phase coefficient, the phase given to a wave front by said diffractive optical portion is represented by a follows formula,

φ

(h)=(2π

/λ

d)·

(C₂h²+C₄·

h⁴+ . . . +C_2i·

h²ⁱ),

H is a half of the effective diameter of said diffractive optical portion, and f2 is the focal length of said second lens unit.

15. A zoom lens system according to claim 12, further comprising a third lens unit disposed on a rearward side of said second lens unit.

16. A zoom lens system according to claim 12, further comprising a third lens unit having positive optical power, said third lens unit being disposed on a rearward side of said second lens unit;

and a fourth lens unit having positive optical power, said fourth lens unit being disposed on a rearward side of said third lens unit.

17. A zoom lens system according to claim 16, wherein said first lens unit, said second lens unit, said third lens unit, and said fourth lens unit are moved for zooming.

18. A zoom lens system according to claim 16, wherein said first lens unit, and said third lens unit are not moved for zooming, and said fourth lens unit is moved for zooming.

19. A zoom lens system according to claim 12, wherein a following condition is satisfied,

0.2<

|f2/(fw·

ft)^1/2|<

1.5

where f2 is the focal length of said second lens unit, and fw and ft are focal lengths of an entire system at wide-angle end and telephoto end, respectively.

20. A zoom lens system according to claim 12, wherein said zoom lens forms an image on an opto-electric converting element.

23. A camera comprising:

a zoom lens system recited in claim 12;

and

an opto-electric converting element for receiving an image formed by said zoom lens system.