JPS58178313A - Photographic lens - Google Patents

Abstract

PURPOSE:To enable focusing with small driving force, by moving the 3rd and 4th lens groups maong 5 lens groups thereby focusing a titled lens. CONSTITUTION:A titled lens consists, successively from an object side, of the 1st lens group of positive refracting power, the 2nd lens group which has positive and negative lenses and is negative as a whole, the 3rd lens group which is combined with negative and positive lenses, and the 4th and 5th lens groups which have at least one piece of lens of positive refracting power and are positive as a whole. The focusing mechanism is made simple by moving the 3rd and the 4th lens groups integrally. A stop is disposed between the 2nd and the 3rd lens groups to permit satisfactory compensation of an aberration. The aberration is compensated satisfactorily by satisfying the equations I and II where the combined focal length of the 3rd and 4th lens groups are designated as f3, f4, the focal length of the 5th lens group as f5 and the focal length of the entire lens system as F.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a photographic lens, and more particularly to a Gaussian photographic lens that performs focusing by moving some lens groups of the lens system.

Generally, focusing in many Gaussian photographic lenses is performed by moving the entire lens system, and this method is characterized by relatively little variation in aberrations due to focusing. However, since the entire lens system is moved, a large driving force is required to drive it, and the lens barrel is complicated and large.

Therefore, it is required to perform 7 orcasing with a small driving force. For example, it is not suitable for use as an autofocus photographic lens.

On the other hand, the method of performing focusing by moving part of the lens/lens group in the lens system requires less driving force for the lens/lens group, but tends to cause relatively large aberration fluctuations due to focussing. be.

SUMMARY OF THE INVENTION An object of the present invention is to obtain a Gaussian photographic lens that can perform focusing with a small driving force, has little variation in aberrations due to focusing, and is suitable for use as an autofocus photographic lens, for example.

The lens structure of the photographic lens for achieving the object of the present invention is characterized by, in order from the object side, a lens group with positive refractive power, lenses with positive and negative refractive powers, and a second lens group with negative refractive power as a whole. a fourth lens group having at least one lens with positive refractive power and having an overall positive refractive power; and a fourth lens group having at least one lens with positive refractive power and having an overall positive refractive power; It has five lens groups, including a fifth lens group with refractive power, and the focusing is performed by moving the third lens group and the fourth lens group.

In general, in Gaussian photography, there is a method of moving some lens groups in the lens system for focusing. Conceivable. Next, aberration fluctuations in the former method of moving the entire rear lens group will be explained using the attached nine drawings.

FIG. 1 is an explanatory diagram of how light rays pass through the lens system when performing 7 orcasing by moving the rear lens group. A is the front lens group, B is the rear lens group, S is the aperture,
L is the off-axis chief ray. The rear lens group B is a positive lens group, and when the object distance changes from infinity to a short distance, the focusing lens B moves from position B0 to position B and comes to the position shown by the dotted line. At this time, the height at which the off-axis principal ray surface enters the rear lens group 03)K changes from B- to 'Un, and the height of incidence at close range "Bn Fi" is compared to the height of incidence AB at infinity. Due to such fluctuations in the light rays, the coma aberration generated in the rear lens group CB) fluctuates in the direction of over-correction, and as a result, the coma aberration of the entire lens system tends to fluctuate in the direction of over-correction.

Also, for the same reason as mentioned above, the method of focusing by moving only the last lens group with positive refractive power in the rear lens group B will correct coma aberration when focusing on a close object. It tends to fluctuate in the direction of excess. Gaussian photographic lenses that have good symmetry with respect to the aperture generally generate asymmetrical aberrations in the opposite direction in the front lens group and the rear lens to better correct aberrations that arise from the entire lens system. The structure is as follows.

Therefore, if aberration fluctuations due to focusing are corrected by using a lens configuration that reduces the occurrence of coma aberration in the rear lens group (J3), it becomes difficult to correct asymmetric aberrations caused by the front lens group.

In order to eliminate such drawbacks, the photographic lens according to the present invention employs the above-mentioned lens configuration. Focusing of the photographic lens according to the present invention will be explained using FIG.

In Figure 2, the front lens group consists of the lens group and the second lens group, B the focusing lens group consisting of the third lens group and the fourth lens group, and C the fifth lens group. group, S is the aperture, and L is the off-axis chief ray. When focusing on a short distance object as described above, the focusing lens group CB) is at position B. It moves from to position B1 and comes to the position shown by the dotted line. At this time, the height at which the off-axis principal ray surface enters the focusing lens group (B) changes from - to ABn. On the other hand, at that time, the height of the light incident on the fifth lens group varies somewhat from Ao6o to Ao6o.

For this reason, the lens configuration is such that the occurrence of coma aberration is minimized in the focusing lens group CB), and the fifth lens group (C) corrects the coma aberration that occurs in the front lens group and the coma in the opposite direction. I am.

As a result, it is possible to achieve a photographic lens in which aberrations are well corrected from objects at infinity to objects at close distances.

Note that the third lens group and the fourth lens group according to the present invention may be moved independently or may be moved integrally.

By adopting the above-described lens configuration, the photographic lens according to the present invention can perform focusing with a small driving force and can achieve good aberration correction.

In the present invention, it is preferable that K, which simplifies the focusing mechanism on the lens barrel, moves the third lens group and the fourth lens group together. It is preferable that a diaphragm is disposed between the second lens group and the third lens group, which correspond to substantially symmetrical positions.

Furthermore, in order to achieve better aberration correction in the photographic lens according to the present invention, the combined focal length of the third lens group and the fourth lens group, which are the focusing lens group (B), is set to f3,
The focal length of the fifth lens group, which is the 4t lens group (C), is f
When the focal length of the all-lens system is F, (1). , 9 times consistently 0.4 f.

+2) 3 ＜−＜ 8 It is necessary to satisfy the following conditions.

Condition (1) is a condition that determines the range of the focal length of the focusing lens CB), and if the upper limit of this condition is exceeded, the amount of focusing movement of the focusing lens group CB) increases, requiring a large movement space. As the total length of the lens increases, the amount of light on the same side of the screen tends to be insufficient, which is undesirable. If the lower limit value is exceeded, the aberrations generated in this lens group (B) will be discolored, making it difficult to achieve good overall correction. Condition (2) is a condition that determines the range of the focal length of the fifth lens group (C), and if the upper limit of this condition is exceeded, the effect of aberration sharing in this lens group (C) will be reduced. This makes it difficult to effectively correct aberration fluctuations. If the tt lower limit value is exceeded, the amount of aberration generated from the lens group (C) is large, and it becomes difficult to perform good aberration correction for the entire lens group.

Since the present invention has the lens configuration as described above, the lens group for focusing is small, the driving force for focusing is small, and the structure of the lens barrel is also small and simple, and furthermore, the focusing lens group is small and the driving force for focusing is small. It has the characteristic 4 that there is little variation in aberrations caused by the lens, and the driving force for focusing is small, making it suitable as an autofocus photographing lens.

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
i is the i-th lens thickness and air gap in order from the object side,
Ni and ν1 are the refractive index and Abbe number of the glass of the i-th lens in order from the object side, respectively.

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[Brief explanation of the drawing]

Fig. 1 is an explanatory diagram of a conventional focusing method, Fig. 2 is an explanatory diagram of a focusing method according to the present invention, and Figs. 3 and 4 are respectively for numerical example 1 of the present invention when the shooting distance is infinity and the lens When the focal length of the system is F, -15,
5 and 6 are cross-sectional views of the lens at 5F, respectively, when the photographing distance of Numerical Example 1 of the present invention is infinity, -IEh,
Various aberration diagrams at 5F, Figures 7 and 8 are cross-sectional views of the lens when the photographing distance is infinity and -15,5F, respectively, in Numerical Example 2 of the present invention, Figure 9, and Figure io. are various aberration diagrams when the photographing distance is infinity and -15.5F in Numerical Example 2 of the present invention, respectively. In the figures, M is the meridional image plane and S is the sagittal image plane. IJJ 216 correct transverse aberration (IJJ216 correct printing (I) *4, difference (Y'=034) sine per I (Y'=034) Vines (Y′・θwoko)

Claims (1)

[Claims] 11) A lens group with positive refractive power in order from the object side. A second lens group that has lenses with positive and negative refractive powers and has an overall negative refractive power, and a third lens group that has lenses with negative and positive refractive powers bonded together.
a fourth lens group having at least 41 lenses with positive refractive power and having an overall positive refractive power; and a fourth lens group having at least 41 lenses with an overall positive refractive power; It has five lens groups: a fifth lens group. A photographic lens characterized in that focusing is performed by moving the third lens group and the fourth lens group. (2) The photographic lens according to claim 1, wherein focusing is performed by integrally moving the third lens group and the fourth lens group. (3) The photographic lens according to claim 2, characterized in that an aperture is provided between the second lens group indicated by # and the third lens group. <4) The combined focal length of the third lens group and the fourth lens group is 13.4 m, and the focal length of the fifth lens group is f9. The photographic lens according to claim 1, wherein the photographic lens satisfies the following conditions: 0.9〈Nasaki〈1.4〈3〈=5-〈8, where F is the focal length of the entire lens system.