JPS5834810B2 - telescope lens - Google Patents

Description

[Detailed description of the invention] The present invention relates to a telephoto lens.

In the design of telephoto lenses, efforts have been made to make them smaller and lighter in recent years, but a method of extending the entire optical system for focusing is still used.

In this method, the larger the focal length, the more
The amount of extension increases, and in super-telephoto lenses, the close distance is limited due to constraints from the mechanical structure, including movement of the aperture position, due to the large amount of extension.

In order to eliminate this drawback, focusing using a front lens extension method like in a zoom lens, or focusing using a macro method in which a part of the lens is extended, can be considered, but the possibilities have been pointed out for Gaussian optics. Even if there were, none of them were satisfactory in terms of aberrations.

The present invention provides a first converging lens group, a second diverging lens group, and a third converging lens group.
Consisting of three convergent lens groups, the first convergent group and the second diverging group form an almost afocal system for objects at infinity,
It is a telephoto lens system that performs focusing by moving the second diverging lens group on the optical axis while keeping the first and third converging lens groups fixed.It is a telephoto lens system with very little aberration fluctuation at short distances, and is extremely The objective is to provide a lens system with a simple configuration.

In the configuration of the present invention, the focal length of the first group is fl, the focal length of the second group is fl, the focal length of the third group is f3, and the composite focal length of the entire system is F. Since it is a telephoto lens, it is necessary to satisfy F>fl, and it is also necessary that fl<f3 in order to reduce the amount of movement of the second group for focusing.

Therefore, when the first group is extended, the amount of extension is smaller than when the entire assembly is extended.

However, if the second group is moved back by the same amount without moving the first group, the image point of the second group must always be at (1), so the effect is the same as if the first group were extended. This makes the lens barrel structure very simple, making focusing easier, and making it smaller and lighter, making it more portable.

Also, if the F number of this optical system is N, a reasonable aberration correction can be provided that satisfies the condition 3, that is, if it is smaller than the lower limit of 1.8 in the conditional expression, the first converging lens group will have excessive spherical aberration with about 3 components. This tends to require correction, and the burden of correction falls on the second diverging lens group and the third converging lens group, making it difficult to balance aberrations at infinity and near distance.

If the upper limit exceeds 3.0, the burden on the first convergent group will be reduced, but the total length of the lens system will have to become longer, which is not practical.

Furthermore, in order to prevent fluctuations in aberrations due to lowering of the second group, the first group must have at least two components.

Here, the radius of curvature of the first component of the first convergent group is rl and r2 in order from the object side, and the radius of curvature of the object-side surface of the second component is r3, and the radius of curvature of the surface of the second component on the object side is r3, and The radius of curvature of the surface must be rt.

Outside this range, (1) aberration fluctuations between the object point and a close object point cannot be suppressed;

To be more specific, the three-group telephoto lens of the present invention has the following features:
Fluctuations in aberration due to changes in distance to the object point must be kept as small as possible, and this condition is especially necessary to maintain stability with respect to spherical aberration and astigmatism.

Regarding spherical aberration, the first group is supplemented independently, and
It is possible to correct astigmatism with two groups, the second group and the third group, and to keep the first group considerably undercorrected for astigmatism, and to cancel it out to a value close to zero by the second group. This was found to be the best condition for maintaining the overall stability of each aberration.

If the lower limit of the above conditions is exceeded, the spherical aberration in the first group will be undercorrected, and the astigmatism as a whole will fluctuate significantly on the negative side.

If the upper limit is exceeded, the opposite tendency becomes significant, and a stable aberration state cannot be maintained.

Furthermore, in order to efficiently distribute aberration correction to each component,
The second component of the first convergent group is separated by an air interval, and this air lens is actively utilized.

That is, by separating the second component of the first convergent group, there is a degree of freedom in which only chromatic aberration can be corrected independently on both sides of this air lens, and color changes due to spherical aberration, color changes due to curvature of field, etc. can be subtly corrected. This can be corrected.

Further, by forming the second diverging group into two components, it is possible to suppress fluctuations in various aberrations when the object is at a short distance.

Further, chromatic aberration can be stabilized simply by providing a bonding surface on one of the components, achieving achromatization of the entire diverging group, and considering the balance with the achromatic state of the first converging group.

In order to suppress color changes due to field curvature, it is desirable to bond the first negative lens component in the second diverging group.

In this way, both the first convergent group and the second diverging group can account for aberration fluctuations at short distances, so when the angle of view is relatively small, the third group mostly absorbs spherical aberration. It is possible to configure the lens with only one self-lens component that satisfactorily corrects only the lens component.

However, the curvature of the object side surface of this positive lens component is r.

, let that of the image side be r■.

> r■ It is necessary to satisfy the condition.

If this condition is exceeded, it becomes difficult to achieve a good balance between spherical aberration and the sine condition, and the above-mentioned spherical aberration can be controlled independently by the first group, or by the second and third groups. The correction method of correcting the image cannot be sufficiently achieved, and it becomes difficult to prevent deterioration of imaging performance at short distances.

Next, examples of the present invention will be shown.

However, f is the combined focal length of the entire system ro, r2, ... is the radius of curvature of each lens from the object side dl, d2, ... is the center thickness of each lens and the air gap nl , n2, . . .; ν1, ν2, .

In Example 1, the imaging magnification of 1/10 is obtained by lowering the second diverging lens group by 1.334.

FIG. 3 shows various aberrations in this example.

Next, a second example will be shown.

In this embodiment, the lens type described in (a) is used as a super-telephoto lens, and the telephoto ratio is kept small.

In super-telephoto lenses, an increase in the secondary spectrum is a major obstacle, so it is necessary to devise ways to sufficiently correct the secondary spectrum in the first convergent group. It is divided into both lenses to change the apparent partial dispersion ratio and has the role of reducing the secondary spectrum.

Example 2 In Example 2, an imaging magnification of 1/10 is obtained by lowering the second diverging lens group by 1 mm.

FIG. 4 shows various aberration diagrams in this example.

As described above, the first convergent lens group, the second diverging lens group,
It is possible to obtain a telephoto lens system consisting of three groups, the third converging lens group, and focusing by moving down the second diverging lens group, with extremely little variation in aberrations at short distances.
By configuring the convergent group with only one component, it is now possible to achieve good performance without having to make the lens thicker.

According to the present invention, it is possible to obtain a high-performance telephoto lens that is smaller in size and more convenient to operate than ever before.

[Brief explanation of drawings]

1 and 2 are cross-sectional views of the lens systems of the first and second embodiments of the present invention, respectively, and FIGS.
FIG. 6 shows diagrams of various aberrations in the second example.

Claims (1)

[Scope of Claims] 1 Consists of three lens groups, a first convergent lens group, a second diverging lens group, and a third convergent lens group, in order from the object side, and the first convergent lens group and the second diverging lens group focus at infinity. It forms an almost afocal system with respect to the object, and the overall focal length is F.
, when the focal lengths of the first convergent lens group, the second diverging lens group, and the third convergent lens group are fl, f2, and f3, respectively, there is a relationship that approximately holds true, and the following conditions are satisfied; Focusing on an object at a closer distance is performed by lowering the second diverging lens group with the three converging lens groups fixed, and the first converging lens group sequentially includes a biconvex first positive lens from the object side; The second diverging lens group includes at least three components, a second positive lens and a first negative lens, the second diverging lens group includes at least one achromatic negative lens component, and the third converging lens group teeth,
It consists of only one positive lens component, and the radius of curvature of the first component of the first converging lens group is set as rl, r2, r2,
Similarly, the radius of curvature of the object-side surface of the second component of the first convergent lens group is r3, the radius of curvature of the final surface of the first convergent lens group is ro, and the third positive component of the third convergent lens group is Let r be the radius of curvature of the object-side and image-side surfaces of the lens component, respectively. , rl, a telephoto lens optical system is characterized in that it satisfies the following conditions.