JP2832369B2 - Zoom lens system capable of quasi-super wide angle - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a zoom lens system capable of quasi-super wide angle used for a video camera or the like.

[Conventional technology]

In recent years, video cameras and the like have been shooting images ranging from wide-angle to telephoto by using a zoom lens system.
In particular, a four-group zoom lens system is widely used. However, in the range where the shooting magnification from wide angle to telephoto can be changed,
Since there is a limit depending on the lens to be used, it is usually set in a frequently used range, and particularly when a wider angle is required, a wide-angle auxiliary lens is attached in front of the first lens group. However, since this auxiliary lens is attached in front of the first lens group, it has a disadvantage that it is large in size and heavy in weight, impairs operability and costs.

[Means for solving the problem]

In view of this situation, the present invention includes, in order from the object side, a positive first lens group, a negative second lens group, a positive or negative third lens group, and a positive fourth lens group. A zoom lens system that moves the focal length from wide angle to telephoto by moving the lens and the third lens group along the optical axis to change the air gap therebetween, wherein the first lens group is an object. A front group having a negative meniscus lens having a convex surface directed toward at least one object side from the side, and having a negative refractive power as a whole, and a rear group having a positive refractive power located on the image surface side from the front group. A quasi-super-wide-angle zoom lens system characterized in that a quasi-super-wide angle can be obtained by moving the front group of the first lens group toward the object side at the focal length at the wide-angle end.

[Action]

In the present invention, by moving the second lens group and the third lens group, zooming from a wide angle to a telephoto state can be usually performed, and a quasi-super wide angle lens having a wider angle than the wide angle photographing system can be obtained. In order to obtain a photographic system, the first lens group is composed of a front group having a negative refractive power as a whole, comprising a negative meniscus lens having a convex surface directed toward at least one object side from the object side, and a first lens group located on the image plane side. Moving the front group of the first lens group to the object side and moving the third lens group to the object side or image side at the wide-angle end focal length. Thereby, a quasi-super wide angle can be achieved while maintaining good imaging performance.

In a first diagram showing a lens configuration and the moving mode of the zoom lens system according to the present invention, 1 is made from a group 1 _projection after the previous group 1 _concave and positive refractive power of the negative refractive power, a positive focal length by compositing A first lens group 2, a second lens group having a negative composite focal length,
Reference numeral 3 denotes a third lens unit having a negative combined focal length, 4 denotes a fourth lens unit having a positive combined focal length, S denotes an aperture, and P 'denotes an image plane. In addition, the front group 1 _{concave with} negative refracting power is not limited to one _concave lens, and may be a lens assembly having two or more negative composite focal lengths.

In FIG. 1, the second lens group 2 and the third lens group 3 are moved along the optical axis to move from the wide-angle end (W) to the telephoto end (T).
When zooming, the first lens group 1 and the second lens group
Air space D ₁ of the between the lens unit 2 is increased, the air gap D ₂ between the second lens group 2 and the third lens group 3 is reduced. During zooming, the first lens unit 1, the stop S, and the fourth lens unit 4 are fixed.

In order to form an even shorter focal length from the state at the wide-angle end (W) to achieve a wide angle, the first state at the wide-angle end (W) is required.
While the rear group 1 _convex of the positive refractive power in the lens group 1 is fixed, the front group 1 _concave of the negative refractive power on the object side is further moved to the object side.
At this time, in order to correct the image point position, the third lens group 3 is slightly moved to the stop S side. The amount of movement of the front group 1 _concave negative refractive power (delta) is determined by the intermediate super wide angle focal length f _SW and the negative refractive power of the front lens group 1 _concave lens power desired (1 / f _{1 female).}

Focusing in the range from the wide-angle end (W) to the telephoto end (T) is mainly performed by moving the first lens unit 1 along the optical axis. Wide-angle end (W) to semi-super wide-angle end (S.
In the range of W), the rear group 1 of the positive refractive power in the first lens group 1
_Convex , second lens group 2, third lens group 3, fourth lens group 4
Focusing is performed by either of the above. This allows
A quasi-super wide angle (SW) imaging system having a shorter focal length than the wide angle end (W) can be configured.

In the above description, when the combined focal length of the third lens group 3 is positive, the wide-angle end (W) to the quasi-super-wide-angle end (SW)
To again forming the imaging system to the front group 1 _concave negative refractive power while fixing the group 1 _convex after a positive refractive power of the first lens group 1 is moved toward the object side, for correcting the image point The third positive lens group 3 is slightly moved to the object side. Depending on the relationship between the object distance and the depth of focus, it may not be necessary to move any of the lens groups to correct the image point position.

In the present invention, it is desirable to satisfy the following conditions.

(1) .0.2 <| Δ / f ₁ | <1.6 Here, f ₁ is the combined focal length of the first lens unit 1, and Δ is the amount of movement of the front lens unit 1 _concave with negative refractive power.

If the lower limit of the conditional expression is not satisfied, the change rate of the angle of view at which the quasi-super wide angle is reduced becomes smaller than the angle of view at the wide angle end, and it becomes difficult to achieve the quasi-super wide angle. On the other hand, if the lower limit of the conditional expression is not satisfied, the entire lens system becomes large, the weight increases, and the aberration fluctuation increases.

〔Example〕

 Hereinafter, numerical examples according to the present invention will be described.

 The lens configuration in FIG. 2 is as follows.

The first lens group 1 includes a negative meniscus lens L ₁ having a convex surface directed toward the object side, the second lens L ₂ of the positive biconvex, and a positive meniscus lens L ₃ Metropolitan having a convex surface directed toward the object side. The second lens group 2, a negative meniscus lens L ₄ with a convex surface toward the object side, a cemented lens L ₅ + L ₆ of a positive lens L ₆ toward the negative lens ₅ and the convex surface toward the object side biconcave Consists of The third lens group 3 is composed of a negative meniscus lens L ₇ with a concave surface to the object side. The fourth lens group 4, a positive lens L ₁₁ and convex to the object side of the negative meniscus lens L ₁₀ with a concave surface and a positive lens L ₈ biconvex the positive lens L ₉ and the object side of the biconvex biconvex a negative lens L ₁₂ toward a positive lens L ₁₃ and a bi-convex. L ₁₄ is a low pass filter consisting of a plane-parallel plate. Aperture S is 3rd
It is arranged between the lens group 3 and the fourth lens group 4.

In the following description of the numerical examples, m: surface number sequentially counted from the object side r _i : radius of curvature of the i-th lens surface counted from the object side d _i : i-th lens component counted from the object side N _i : the refractive index of the i-th lens component counted from the object side with respect to the d-line ν _i : the Abbe number of the i-th lens component counted from the object side f ′: composite focal point of the whole system Distance Bf ': Back focus.

 The specific configuration of the embodiment is as shown in the table below.

f 'Bf' Angle of view SW 6.92 10.95 69.0 ゜ W 9.32 10.95 50.3 ゜ T 49.53 10.95 9.1 ゜ d ₂ d ₆ d ₁₁ d ₁₃ SW 42.8 1.07 29.06 4.73 W 1.07 1.07 28.39 5.40 T 1.07 23.38 4.54 6.94 | Δ / f ₁ | = 0.646 The aberration curve according to this specific configuration is as shown in FIG.

The various aberrations in the aberration curve diagrams of the above embodiments indicate that they are sufficiently practical.

〔The invention's effect〕

As is apparent from the above description, according to the present invention, the front lens unit having the negative refractive power on the object side of the first lens unit is further moved toward the object side from the wide-angle imaging system, and the image point is shifted by the third lens unit. By performing the position correction, it is possible to provide a zoom lens system capable of forming a quasi-ultra-wide angle photographing system that can easily form a quasi-ultra-wide angle photographing system while maintaining good imaging performance.

[Brief description of the drawings]

FIG. 1 is a diagram showing the movement of a zoom lens system according to the present invention,
FIG. 2 is an arrangement diagram of each lens group when the lens groups of the embodiment are set to a quasi-super wide angle (SW), a wide angle (W), and a telephoto (T)
FIG. 3 is an aberration curve diagram of the example. L _1, ... L _14: first lens, second 14 lens X: an optical axis, S: throttle _{r 1, r 2, ... r} 26: the radius of curvature d _1, d ₂ of each lens surface, ... d _26: each lens Thickness or air spacing

Claims (1)

(57) [Claims] 1. A first lens group, a second negative lens group, a third positive or negative lens group, and a fourth positive lens group in this order from the object side. The second lens group and the third lens A zoom lens system that continuously changes a focal length from a wide angle to a telephoto position by moving a group along an optical axis to change a mutual air interval, wherein the first lens group is at least one lens from an object side. A wide-angle lens comprising a front group having a negative meniscus lens having a convex surface facing two object sides and having a negative refractive power as a whole, and a rear group having a positive refractive power and being positioned closer to the image plane than the negative meniscus lens. A quasi-super-wide-angle zoom lens system, wherein the front lens group of the first lens group can be moved toward the object side at an end focal length to achieve a quasi-super-wide angle.