JPS5866908A - Compact telephoto zoom lens - Google Patents

Abstract

PURPOSE:To obtain a telephoto zoom lens of F/5.6 brightness and about 0.77 telephoto ratio which is compact and is subjected to aberration correction satisfactorily, by specifying the focal lengths of 4 kinds of lens groups and the focal length at the telephoto end of the entire system. CONSTITUTION:The 1st lens group of positive refracting power for focusing, the 2nd lens group of negative refracting power for variable powers, the 3rd lens group of positive refracting power for correcting the movement of an image point, and the 4th lens group for imaging are disposed successively from the object side. Nearly an afocal optical system is constituted of the 3rd lens from the 1st lns group. When the focal lengths of the 1st lens group, the 2nd lens group and the 4th lens group are defined respectively as f1, f2, f4 and the focal length at the telephoto end of the entire system of the zoom lens is defined as fT, the conditions of the equations 1-3 are satisfied.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a compact photographic X/f1 telephoto lens, in particular a compact and high-performance lens with a focal length of 400° on the telephoto side and a % zoom ratio of about 4. This relates to a telephoto zoom lens.

Generally, telephoto type photographic zoom lenses have a variable power ratio of 3.
When the magnification exceeds the so-called high variable power ratio, the lens structure inevitably becomes complicated in order to correct aberrations. In particular, it was necessary to correct aberrations by increasing the number of lenses in the zoom lens group and the focusing lens group in order to correct aberration fluctuations due to zooming. Due to the increase in the number of lenses, telephoto zoom lenses with high zoom ratios tend to be larger in size, are more expensive to manufacture, and the optical performance is not sufficient as a photographic zoom lens despite the increase in the number of lenses. I didn't like it.

For this reason, telephoto zoom lenses with high zoom ratios have not been used much in the past.An object of the present invention is to provide a compact telephoto zoom lens with high zoom ratios for photography that has daytime performance.

The features of the lens configuration of the telephoto zoom lens for achieving the object of the present invention are, in order from the object side, the first lens group has a positive refractive power for focus adjustment, and the second lens group has a negative refractive power for zooming. A lens group, a third lens group with positive refractive power for image point movement correction, and a fourth lens group for focusing, and the lens group to the third lens constitute a near-afocal optical system. , when the focal lengths of the lens group, the second lens group, and the fourth lens group are respectively f, , f, , f4, and the focal length of the entire zoom lens system at the telephoto end is fr, (1) 0. 37<ft/fT<0.50 (2)
0.08<fJfT<0.13(8) 0.38'<
Condition (1) is related to the focal length of the lens group, and if the upper limit of condition (1) is exceeded, it becomes a compact telephoto zoom lens. If the lower limit value is exceeded, it is possible to make the lens compact as a telephoto zoom lens, but the aberration correction on the telephoto side due to zooming becomes insufficient, which is undesirable.

Conditional expression (2) relates to the focal length of the second lens group, and if the upper limit of conditional expression (2) is exceeded, the amount of movement of the second lens group for zooming will be large. It is not possible to achieve this, and the diameter of the front lens becomes large, which is undesirable. If the lower limit is exceeded, the amount of movement of the second lens group for zooming will be small, and the telephoto zoom lens can be made more compact, but the air gap between the lens group and the second lens group will become larger than necessary. This is not preferable because the 4m area around the screen becomes insufficient.

Conditional expression (3) relates to the focal length of the fourth lens,
If the upper limit of conditional expression (8) is exceeded, the focal length will be large and the aberration - positive will be advantageous, but the diameter of the diaphragm disposed in front of the fourth lens group will become large, which is unfavorable for operation, and if the lower limit is If it exceeds this, the aperture diameter will become smaller, which is preferable, but the focal length will become shorter, making it difficult to properly correct aberrations.

The present invention can achieve a compact telephoto zoom lens with good aberration correction using the lens configuration described above, but in order to achieve even better aberration correction, it is preferable to satisfy the following conditions. The first lens has a positive refractive power, and the first meniscus has a negative refractive power, with its convex surface facing the object side.
A laminated first lens in which two lenses and a thirteenth lens with positive refractive power are laminated together, or a meniscus first lens with negative refractive power with the convex surface facing the object side in order from the object side and a twelfth lens with positive refractive power. The first lens is a laminated lens with a positive refractive power, and the 13th lens has a positive refractive power.The third lens group includes, in order from the object side, a biconvex third lens with a positive refractive power, and a 32nd lens with a positive refractive power. A laminated third lens is formed by laminating a lens and a 33rd lens with negative refractive power, or a laminated third lens is formed by laminating a third lens with positive refractive power and a 32nd lens with negative refractive power. By making the lens group as described above, it is preferable to correct aberrations on the telephoto side, particularly for correcting astigmatism. In particular, in the former type, in which the first lens with positive refractive power precedes the lens, the rear principal point moves closer to the object side, resulting in a shorter distance between the lens group and the second lens group, which reduces the total length of the lens. In addition, the radius of curvature of the bonding surface of the first lunion bonded together is small, and correction of the axial color aberration can be easily performed.

By making the third lens group have the above-mentioned lens configuration, coma aberration can be well corrected at the zoom position near the middle, and by moving the principal point of the third lens group toward the object side. This prevents the second lens group and the third lens group from interfering with each other when the lens reaches the zoom position toward the telephoto side.

Furthermore, by dividing the third lens group into two groups, aberration fluctuations due to zooming can be reduced.

=j and has a telephoto ratio of 0.774 degrees, achieving a compact telephoto zoom lens with excellent aberration correction.

Next, numerical examples of the present invention will be shown. In numerical examples R
i is the radius of curvature of the i#th lens surface in order from the object side, D
l is the first lens thickness and air spacing in order from the object side,
Ni and yi are respectively calculated from the object side to mi by the glass d' refractive index of the first lens and the Atsube number.
χk 2χ χ gu 22χ χ kχZ
22 Z 22 2 22 Z 22 2 2
2Rgu << arm 2csu k fable χ2 wealth χ fable fable k susu fableχ
Dirt < Arm < Arm 22 2
Z 2χ 22 2 22 2 2χlR<
＼ S-ze

[Brief explanation of the drawing]! Embodiment No. 5 of the present invention is shown in FIGS. 1 to 5, respectively.
FIGS. 6 to 8 are cross-sectional views of a telephoto zoom lens according to a first embodiment of the present invention. 9 to 11 show Example 2 of the present invention. 12 to 14 show Example 3 of the present invention. 15 to 17 show Example 4 of the present invention. 18 to 20 are various aberration diagrams at zoom positions on the wide-angle side, intermediate side, and telephoto side, respectively, in Example 5 of the present invention. In the figure, S is a sagittal image plane, and M is a meridional image plane. Patent applicant Canon Co., Ltd. Tsutsumu 4 Jyumen Shukucha 1p11 1 song collection A certain Uemoto [
1 Hitsugi most Non, Gu, Aberration Distortion aberration bead 1
IIl Kistop ll, aberration i curved slope cage @ collection egg, e, stile difference 1 curved board' floor @ weir non-jiangyanen curved tea bed [with] aberration astigmatism, convergence distortion spherical difference 111 people,
Aberration Distortion aberration

Claims (1)

[Claims] (1) In order from the object side: a first lens group for focus adjustment with positive refractive power, a second lens group for zooming with negative refractive power, and an image point movement of positive refractive power. A wc3 lens group for correction and a fourth lens group for imaging are arranged, and the third lens group constitutes an almost afocal optical system, and the third lens group, the second lens group, and the fourth lens group are arranged. The focal length of each lens group is f1. ft, f, and when the focal length at the telephoto end of the entire zoom lens system is fT, 0.37<mu/7T (0,50 0,08<fJ f T <0.13o, a 8<f
A compact telephoto zoom lens that satisfies the following condition: Jfr < 0.46. (2) The first lens group has a first lens with positive refractive power, a meniscus 12th lens with negative refractive power with its convex surface facing the object side, and a 13th lens with positive refractive power, which are laminated in order from the object side. The front third lens group includes, in order from the object side, a biconvex third lens with positive refractive power, a 32nd lens with positive refractive power, and a 33rd lens with negative refractive power. 2. A compact telephoto zoom lens according to claim 1, further comprising a laminated third lens. (8) The first lens group includes, in order from object-1j, a meniscus first lens with a negative refractive power with its convex surface facing the object side, a bonded first lens with an m12 lens with a positive refractive power, and a positive lens. It has a 13th lens with a refractive power, and the front 3rd lens group has a laminated 3rd lens in which a 3rd lens with a positive refractive power and a 32nd lens with a negative refractive power are laminated together. What to do! ! ! A compact telephoto zoom lens according to claim 1, wherein the j value is wc. (4) The first lens group has a first lens with positive refractive power, a twelfth meniscus lens with negative refractive power with its convex surface facing the object side, and a thirteenth lens with positive refractive power, which are laminated in order from the object side. The third lens group has a laminated third lens in which a third lens with a positive refractive power and a third lens with a negative refractive power are laminated together. A compact telephoto zoom lens according to claim 1, characterized in that: (5) The first lens group includes, in order from the object side, a meniscus first lens with a negative refractive power whose convex surface faces the object side, a twelfth lens with a positive refractive power, and a positive refractive lens. The third lens group has a 13th lens with a positive refractive power, and a 32nd lens with a positive refractive power, and a 33rd lens with a negative refractive power are attached in order from the integral side. A compact telephoto zoom lens according to claim 1, characterized in that it has nine laminated third lenses.