JPH04147110A - Zoom lens - Google Patents

Abstract

PURPOSE:To secure a sufficiently short minimum photographic distance at a telephoto end and realize the shortest object distance of almost 0 m at a wide-angle end by specifying the movement quantity of a focusing lens element. CONSTITUTION:The conditions when the focusing lens element moves monotonously on the optical axis are so set as to satisfy expressions I and II. Here, A is the movement quantity of the focusing lens element at the time of focusing from an infinite-distance body to the closest body with optional focal length, B the movement quantity of the focusing lens element at the time of focusing from the infinite-distance body to the closest body at the wide-angle end, C the movement quantity of the focusing lens element from optional focal length to the wide-angle end at the time of zooming with the infinite body distance, and X a coefficient (fs: focal length of the whole system at the wide-angle and) when the closest body distance at the wide-angle end is represented as XfS. Consequently, while the sufficiently short minimum object distance at the telephoto end is secured, the minimum photographic distance at the wide-angle end is shortened almost to 0 m.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a zoom lens, and is particularly applicable to small cameras such as video cameras.

[Conventional technology]

In recent years, electronic components for video cameras and the like have been reduced in cost, made more compact, and improved in performance at a considerable speed. Furthermore, high-resolution image sensors are also used for consumer use, and their share in the market is increasing. For this reason, optical systems are now required to be compact and have high specifications as well.

For example, in the past, most zoom ratios were around 6x, but many have come out with high zoom ratios of 8x or more. Shortest object distance (7 lens systems have a minimum object distance of 1 m or less).

Instead of the conventional focusing method that involves extending the front lens, there are many so-called inner focusing methods that move lens components other than the front lens. The feature of this inner focus method is that in order to focus on a certain object distance at the telephoto end, the lens component is moved from a position corresponding to the object distance 5l = (1) 7 infinity, and the same object at the wide-angle end. Comparing the amount of movement relative to the distance, the amount of movement at the wide-angle end is much smaller. In addition, in terms of size, the diameter of the front ball can be made smaller compared to the front ball feeding method, so the weight can be reduced.

In the case of conventional inner focus zoom lenses,
There are many such as can be seen in Japanese Patent Application Laid-Open No. 59-28120. Furthermore, in JP-A No. 55-40447, the front element, variator, compensator, and master lens are each made up of one component, similar to the front element extension type zoom lens, and the compensator is movable even during 7-point adjustment. , object distance S
When l is at infinity, the compensator/focusing lens moves in exactly the same way as in the case of the front lens extension method.

In such a lens system, when the shortest photographing distance at the telephoto end is shorter than about 1.2 m, the shortest photographing distance at the wide-angle end is shorter than Om.

In other words, the lens surface focuses on scratches and dust inside the lens, which is undesirable as it causes AF malfunction. Furthermore, even if scratches and dust are not completely focused, their shadows will appear on the screen, resulting in an unpleasant image.

In the embodiments of JP-A-64-35515, the object distance S1
Even when the lens is at infinity, the 7-ocan lens can be seen moving monotonically from the telephoto end to the wide-angle end. However, in this embodiment, the trajectory of the four-force non-lens is designed to always lie on the same curve at any given object distance! The shortest shooting distance at the wide-angle end is 0.5
It is difficult to say that it satisfies the needs of the world at m~0.3□.

[Problem to be solved by the invention]

The present invention secures a sufficiently short minimum object distance at the telephoto end, and realizes a minimum object distance of about 0m at the wide-angle end, and the hitting position of the seven focusing lens components is fixed regardless of the focal length. Therefore, it is an object of the present invention to provide a zoom lens in which the position of the AF is constant and, therefore, the position can be easily and accurately controlled and the AF malfunctions are less likely to occur.

[Failure to solve the problem]

In order to achieve the above object, the present invention includes a focusing lens component that performs focusing by moving the lens component other than the lens component closest to the object, and zooming from the telephoto end to the wide-angle end at an arbitrary object distance. A zoom lens in which the focusing lens component moves monotonically on the optical axis when performing the focusing, is characterized by satisfying the following conditions: C=A−B O≦X<1.5, where A is arbitrary. The amount of movement of the focusing lens component from an arbitrary focal length to the wide-angle end when zooming is performed at a focal length of , where B is the closest object to the wide-angle end, and C is the closest object to the infinite object at the wide-angle end; X is a coefficient when the closest object distance at the wide-angle end is expressed as Xfs (where fs is the focal length of the entire system at the wide-angle end).

When the above conditions are satisfied, the shortest object distance at the wide-angle end is 5.
1wm1n becomes S l wmin = X fs, but
Normally, a lens system is equipped with a 7-domain for the purpose of preventing ghosts, etc., and 51wm1n can be regarded as the actual tip position of the lens.

When zooming at S1=■, the direction of the amount C by which the focusing lens component moves is normally A.

Although it is in the same direction as B, if the shortest object distance at the telephoto end is longer than about 1.2 m, C will be in the opposite direction to A and B, and the amount of → movement generated by the force single lens at the wide-angle end will be The distance becomes sharper than the total amount of movement at the telephoto end. However, since consumer video lenses are often used indoors, the shortest object distance at the telephoto end is required to be at least about 1.2 m. At this time, the focusing lens component can remain stationary during zooming at the object distance S1-■.

By adopting these configurations, it is possible to realize a lens system with a simple lens barrel configuration that ensures a sufficiently short minimum object distance at the telephoto end and does not cause the lens to cannon toward the inside from the tip of the lens at the wide-angle end. Either you want a configuration like this or you end up focusing.

Although it is possible to adopt a configuration that prevents focusing inside the lens, it is necessary to provide a member that restricts the 7-focus lens component only between the shaded areas, as in the conventional example shown in FIG. There is. In this case, the mechanism becomes quite complicated, and the repeatability has an error of about several tens of millimeters.

This error is several tens of centimeters when converted to the object distance at the wide-angle end. If configured as in the present invention, a mechanical contact can be provided at a fixed location, and if the focusing lens position reference is cleared to 0 at this contact position, the repeatability will be sufficiently accurate.

Incidentally, it is preferable that the zoom lens is composed of the following five lens components. That is, in order from the object side, a fixed second lens component having a positive refractive power, a second lens component having a negative refractive power and moving on the optical axis mainly to change the focal length, and a second lens component having a negative refractive power and moving on the optical axis mainly to change the focal length. a third lens component that has refractive power and moves on the optical axis to correct the image point position; a fourth lens component that has positive refractive power and moves on the optical axis for focusing; and a fixed fifth component having refractive power. With this lens configuration, it becomes easy to satisfy the above-mentioned conditions, and a compact zoom lens with high magnification can be obtained.

Furthermore, it is desirable that the zoom lens satisfies the following conditions.

0.06< ψ・T < 0.25 However, T is the refractive power of the fourth lens component; T is the distance from the lens surface closest to the image side of the fourth lens component to the lens closest to the object side of the fifth lens component at the wide-angle end. is the axial air spacing to the surface.

When ψ·T becomes small beyond the lower limit of the above conditional expression, if T is small, it becomes impossible to focus almost to the tip of the lens at the wide-angle end. Also, if ψ is small, the object distance is 5l at the telephoto end.
It becomes impossible to focus up to approximately 1.2 m, and it is impossible to obtain a zoom lens with sufficient NA specifications. On the other hand, when ψ·T increases beyond the upper limit of the above conditional expression, if T is large, the overall length of the lens becomes long and the diameter of the front lens becomes large, making it impossible to obtain a compact zoom lens. However, if ψ is large, spherical aberration will appear on the under side over the entire zoom range, making it impossible to obtain good imaging performance.

〔Example〕

The specifications of the zoom lens to which the present invention is applied when focusing on an object at infinity are shown below. The flat plate placed on the image side of the fourth lens component is a prism for splitting the optical path that guides the light beam to the focus detection optical system, and the flat plate placed on the image side of the fifth lens component is a dichroic prism or a low-pass prism. It is a flat plate that corresponds to a filter.

Note that the shortest object distance at the telephoto end in the first embodiment is 0.5
m, and the shortest object distance at the telephoto end in the second embodiment is Qm. Further, the values or parameters of the conditional expressions in each example are as shown in the table below.

Table 1 (N'person 14b) Part ■ Example f-66,0~]9,0~88 F8゜-14 Radius of curvature axis upper surface interval Refractive index (Nd) Atsube number (νd) Second example f- 66,3 to 19.0 to 88 F8゜-1,4 Radius of curvature axis upper surface interval Refractive index (Nd) 77 Beam number (νd) Telephoto end (L) of Example, intermediate focal length (M), wide lens component FIG. 7 is a diagram showing a movement curve of a focusing lens component in a conventional zoom lens during zooming, and FIG. 8 is an explanatory diagram illustrating the operating principle of the present invention.

that's all Applicant: Minolta Camera Co., Ltd. No. figure 1I2 figure Glue figure 4 Spherical aberration sine condition Non-night aberration Saturday and Sunday 070 $5 figure SlTm1n=0.5 SlTm1n=0 S1wmin=0

Claims (1)

[Scope of Claims] (1) A focusing lens component that performs focusing by moving a lens component other than the lens component closest to the object, and when zooming from a telephoto end to a wide-angle end at a given object distance, the focusing lens component A zoom lens whose lens components move monotonically on the optical axis is characterized by satisfying the following conditions: C=A-B 0≦X<1.5, where A is any focal point B is the amount of movement of the focusing lens component when focusing from an object at infinity to the nearest object at the wide-angle end; C is the amount of movement of the focusing lens component when focusing from an object at infinity to the nearest object at the wide-angle end; The amount of movement of the focusing lens component from a given focal length to the wide-angle end when zooming at a far object distance; X is the coefficient when the closest object distance at the wide-angle end is expressed as Xfs (however, fs is focal length of the entire system). (2) The zoom lens according to claim 1, wherein the focusing lens component remains stationary during zooming from a telephoto end to a wide-angle end. (3) The zoom lens includes, in order from the object side, a fixed first lens component having a positive refractive power, and a second lens component having a negative refractive power and moving on the optical axis mainly to change the focal length. component, a third lens component that has negative refractive power and moves on the optical axis to correct the image point position, and a fourth lens component that has positive refractive power and moves on the optical axis for focusing. 2. The zoom lens according to claim 1, wherein said fourth lens component is said focusing lens component and said fourth lens component is said focusing lens component. (4) The zoom lens according to claim 3, wherein the zoom lens satisfies the following condition: 0.06<Ψ・T<0.25, where Ψ is the refractive power of the fourth lens component; T is the axial air distance from the lens surface of the fourth lens component closest to the image side to the lens surface of the fifth lens component closest to the object side at the wide-angle end.