Zoom lens system having a diffractive surface

• US 5,982,544 A
• Filed: 07/02/1998
• Issued: 11/09/1999
• Est. Priority Date: 07/03/1997
• Status: Expired due to Term

• Current Assignee: Olympus Optical Corporation Limited (Olympus Corporation)
• Original Assignee: Olympus Optical Corporation Limited (Olympus Corporation)
• Inventors: Ogata, Yasuji
• Primary Examiner(s): HENRY, JON W
• Application Number:
  US09/109,416
• Time in Patent Office: 495 Days
• Field of Search: 359/565, 359/570, 359/571, 359/575, 359/19, 359/15, 359/743, 359/742, 359/680, 359/566
• US Class Current: 359/565
• CPC Class Codes: G02B 15/143103 arranged ++-
• CPC Class Codes: G02B 27/4211 correcting chromatic aberrations G02B27/0056, G02B27/4222, G02B27/4227 take precedence

Abstract

The invention provides a compact yet high-zoom-ratio zoom lens system for use with lens shutter cameras, which is well corrected for aberrations albeit being made up of a small number of lenses. The zoom lens comprises a first lens group G1 of positive refracting power, a second lens group G2 of positive refractive power and a third lens group G3 of negative refracting power. The lens groups move for zooming from the wide angle side to the telephoto side, with a separation between the first and second lens groups becoming wide and a separation between the second and third lens groups becoming narrow. At least one lens group has a diffractive surface therein, and satisfies 1.8<β_T /β_W <4.0 where β_T and β_W are transverse magnifications of the lens group having a diffractive surface at the wide-angle end and the telephoto end of the lens system.

Claims

1. A zoom lens system having a diffractive surface, which comprises, in order from an object side thereof, a positive lens group, a positive lens group, and a negative lens group, said lens groups moving for zooming from a wide angle side to a telephoto side thereof, with a separation between first and second lens groups becoming wide and a separation between second and third lens groups becoming narrow, wherein:

said negative lens group has said diffractive surface therein.

3. The zoom lens system according to claim 1 or 2, wherein said first lens group comprises at least two lenses, and satisfies the following condition (2):

space="preserve" listing-type="equation">15<

ν

.sub.1 -ν

.sub.2 <

25 (2)

where ν

₁ and ν

₂ are Abbe'"'"'s numbers of lenses forming said first lens group.

4. The zoom lens system according to claim 1 or 2, wherein said diffractive surface satisfies the following condition (3):

space="preserve" listing-type="equation">-0.01<

Φ

.sub.DOE <

0 (3)

where Φ

_DOE is a power of said diffractive surface.

5. The zoom lens system according to claim 4, wherein said diffractive surface satisfies the following condition (4):

space="preserve" listing-type="equation">-0.005<

Φ

.sub.DOE <

0 (4)

6. The zoom lens system according to claim 1 or 2, which satisfies the following condition (5):

space="preserve" listing-type="equation">0.4<

Σ

d/D<

1.0 (5)

where Σ

d is a length from a first surface to a final surface, and D is a diagonal length of a film surface.

7. The zoom lens system according to claim 6, which satifies the following (6):

space="preserve" listing-type="equation">0.4<

Σ

d/D<

0.8 (6)

8. The zoom lens system according to claim 1 or 2, wherein said third lens group comprises a single lens.

9. The zoom lens system according to claim 8, wherein said third lens group comprises a plastic lens.

10. The zoom lens system according to claim 8, wherein a lens in said third lens group satisfies the following conditions (7):

space="preserve" listing-type="equation">n.sub.d <

1.65, ν

.sub.d <

50 (7)

where n_d is a d-line refractive index of a lens substrate, and ν

_d is a d-line Abbe'"'"'s number of the lens substrate.

2. A zoom lens system having a diffractive surface, which comprises, in order from an object side thereof, a positive lens group, a positive lens group, and a negative lens group, said lens groups moving for zooming from a wide angle side to a telephoto side thereof, with a separation between first and second lens groups becoming wide and a separation between second and third lens groups becoming narrow, wherein:

at least one lens group has said diffractive surface therein, and satisfies the following condition (1);

space="preserve" listing-type="equation">1.8<

β

.sub.T /β

.sub.W <

4.0 (1)

where β

_T and β

_W are transverse magnifications of said lens group having said diffractive surface at a wide-angle end and a telephoto end of said lens system.