JPS5849908A - Telephoto zoom lens - Google Patents

Abstract

PURPOSE:To correct the spherical aberration, the coma, and the chromatic aberration of a titled lens well, by constituting a variator part with two convex single lenses, where strong concaves face to each other, and a compound lens between a biconvex lens and a biconcave lens and satisfying specific conditions. CONSTITUTION:The variator part of a zoom lens system consists of a concave lens whose strong concave is directed to the image side, a concave lens whose strong concave is directed to the object side, and a compound lens between a biconvex lens and a biconcave lens which are arranged in order from the object side, and conditional expression (1) is satisfied when the focal length of the variator and the focal length of the compound lens are denoted as f2 and fa respectively. Thus, the absolute value of the focal length fa is larger than that of the focal length f2 to lower the refracting power of the compound lens of the variator part, and the spherical aberration, the coma, and the chromatic aberration are corrected well without the influence upon the astigmatism and the distortion.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention provides an almost afocal variable magnification system comprising a focusing part with positive refractive power, a 6-reactor part with negative refractive power, and a compensator part with positive refractive power. This invention relates to a telephoto zoom lens consisting of a relay lens system.

In general, the challenges for telephoto zoom lenses are to improve performance by reducing the secondary spectrum and to make them small and nimble to improve portability. It is well known that it is effective to reduce the secondary spectrum by using low-dispersion glass or fluorite with anomalous dispersion in the focusing part, but since the focusing part has the largest lens diameter, these expensive The use of optical materials would be extremely expensive and therefore not common. Furthermore, as shown in Figure 1, the variator of conventional telephoto zoom lenses is often made up of a cemented lens consisting of a mirror lens, a concave lens, and a convex lens. The radius of curvature of one surface is extremely smaller, and many have a shape similar to a plano-convex lens.

In order to make a part of the HII ether achromatic, it is necessary to make a large difference in the number of spots before and after this joint surface. This cemented surface has a great effect on correcting spherical aberration at the longest focal length, but for the reasons mentioned above, the refractive power of this cemented surface varies greatly depending on the wavelength, and the effect of this cemented surface on spherical aberration also differs depending on the wavelength. become. When the variator section has the configuration shown in Fig. 1, the spherical aberration at the longest focal length is schematically drawn as shown in Fig. 2.

Even if the d-line is well-corrected, the 2-line will be extremely under-corrected, and the C-line will be over-corrected. Even if the secondary spectrum is small, good image quality cannot be obtained if the color shift due to spherical aberration is large. Conventionally, it has been difficult to solve the above drawbacks and make the entire system smaller, so when prioritizing miniaturization, brightness must be sacrificed, and conversely, when prioritizing brightness, some parts of the variator must be sacrificed. The refractive power of the lens had to be weakened and the entire system had to be made larger.

The present invention has a zoom ratio of about 3 times and an angle of view of about 8 degrees at the longest focal length.
We provide a telephoto zoom lens with a brightness of about F4.5, which can satisfactorily correct spherical aberration, coma aberration, astigmatism, distortion and chromatic aberration, and which can achieve a telephoto ratio of 0.9 or less at a low cost. The purpose is to prosper.゛The present invention will be described in detail with reference to the attached drawings.As shown in Fig. 6, in order from the object side, there is a first group as a focusing section having a positive refractive power, and a first group having a negative refractive power. , a second group as a part of the creator that mainly converts the focal length by moving on the optical axis, and a predetermined image plane that has positive refractive power and changes due to the movement of a part of the creator. A zoom lens consisting of a variable magnification system consisting of a third group as part of a compensator that maintains the lens in position, and a relay lens system following the variable magnification system. The variator consists of a concave lens with a strongly concave surface facing the image side, a concave lens with a strongly concave surface facing the object side, and a cemented lens of a biconvex lens and a biconcave lens, and the focal length of a part of the variator is set to f2. When the focal length of the cemented lens of a part of the variator is fa, the following conditions are satisfied, and further, the compensator part has a convex lens P1 and a concave lens N in order from the object side.
The relay lens system consists of a cemented convex lens with a convex lens P2 and a concave lens N2, and a front group as a cemented convex lens with a convex lens P3 and a concave lens N5, in order from the object side, and a strong concave surface facing the object side. Consisting of a concave lens and a double convex lens, the Atsbe number ν
and partial dispersion ratio θ, the convex lens P1 . Let the Atsube numbers and partial dispersion ratios of P2 and P3 be P, θP, and similarly N+, N2
When the Atsube number and partial dispersion ratio of N3 are νN and θN, (21(0,6469−0,001755shiP)〈θP
To explain the theoretical basis of the present invention in detail, firstly, the reason why the color shift due to spherical aberration is as shown in Figure 2 is because the variator part has three elements in two groups as shown in Figure 1, and the convex lens is a plano-convex lens. As mentioned above, this is because the shape is close to that of the above. Therefore, if this convex lens is made into a biconvex lens and the refractive power is distributed on both sides, the effect of this convex lens on spherical aberration will be weakened, and the color shift due to spherical aberration should be improved. If the convex lens is made into a biconvex lens, it becomes impossible to correct variations in various aberrations due to zooming. Therefore, by constructing a part of the variator with two mirror lenses with strong concave surfaces facing each other and a cemented lens of a biconvex lens and a biconcave lens, and weakening the refractive power of the cemented lens, the astigmatism and distortion aberration during zooming can be changed. is corrected by the above two mirror lenses, and the cemented lens can correct spherical aberration, coma aberration, and chromatic aberration without affecting astigmatism and distortion, and the spherical aberration at the longest focal length caused by a convex lens can be corrected. Since the convex lens is a biconvex lens, the refractive power is dispersed on both sides, and the color shift can be significantly improved compared to the part of the variator shown in FIG.

Next, a method for economically reducing secondary wave torque will be described. If the Abbe number ν is plotted on the horizontal axis and the partial dispersion ratio θ is plotted on the vertical axis, the smaller the straight line connecting the glass of the achromatic convex lens and the concave lens, the less the secondary wave torque will decrease. As is well known, low-dispersion glass with high anomalous dispersion that can reduce this inclination is very expensive, and its use in a focusing section with a large lens diameter does not meet the purpose of the present invention. Furthermore, if an inexpensive so-called old lath is selected, this slope tends to increase, and the secondary spectrum increases, making it impossible to achieve the object of the present invention. The present invention uses glass that has a smaller tilt than the old glass and is not very expensive for the compensator part, which has a smaller lens diameter than the focusing part, and the front group of the relay lens. The feature is that the spectrum has been corrected to a level sufficient for practical use. Conventional compensators are often constructed with two elements in one group using old glass, but if glass is selected from among ordinary glasses so that the slope of the above straight line is small, the difference in the Atsube number ν can be increased. Because it is not possible to
If the lens is configured with two lenses per group, the refractive power of the convex lens and the concave lens will become too strong, making it difficult to correct spherical aberration and coma aberration. In the present invention, a part of the compensator is made of four elements in two groups to disperse the refractive power, thereby achieving both reduction in secondary distortion and torque and correction of spherical aberration and coma aberration.

Each conditional expression will be explained in detail below.

(Condition 11 defines the configuration of a part of the variator. When the absolute value of fa becomes larger than the absolute value of f2 and the refractive power of the cemented lens in a part of the variator becomes weak, the cemented lens becomes astigmatic. It becomes possible to correct spherical aberration, coma aberration, and chromatic aberration without affecting aberrations and distortion, increasing the degree of freedom.

Conditions (2) and (3) are intended to reduce the secondary spectrum, and on the diagram with ν on the horizontal axis and θ on the vertical axis, two representative glasses of old glass (n4 = 1 .51680
.

shi = 64.2.0 = 0.5342 > and (nd = 1.6
2004.

Convex lenses P + I P 2 and P3 are on this straight line, and concave lenses N1. For N2 and N3, if the glass is selected from below this straight line, the slope becomes smaller and the secondary spectrum can be reduced.

Next, examples of the present invention will be shown.

Example l F4.65 f2=-40 pack focus-43,22fa=365.82 telephoto ratio
0.878 Example 2 F4.65 f2 knee 40 pack focus = 46.74 fa = 275.89 Telephoto ratio 0.887

[Brief explanation of the drawing]

Figure 1 is a configuration diagram showing an example of a part of a conventional 6Q eta, and Figure 2 is a curve diagram showing color shift due to spherical aberration at the longest focal length when a part of the variator shown in Figure 1 is used. , FIG. 6 is a configuration diagram of an embodiment of the present invention, and FIG. 4 is an aberration curve diagram of spherical aberration, astigmatism, and distortion at each focal length in embodiment 1. FIG. 5 is an aberration curve diagram at each focal length in Example 2. Figure 1 Figure 2 Figure 3 Wl bullet
・1st? ! 465 ・、Tsukimata aki Distorted Romata 4.2"4.2"

Claims (1)

[Claims] 1. In order from the object side, a first group serving as a focusing portion having a positive refractive power, and a #1 group having a negative refractive power and extending on the optical axis.
The second group is a part of a variator that mainly converts the focal length by moving, and the second group is a part of a compensator that has positive refractive power and keeps the image plane at a predetermined position, which changes as the part of the variator moves. A zoom lens consisting of a variable power system consisting of a third group, and a relay lens system following the variable power system, in which a part of the i-variator is arranged in order from the object side. It consists of a concave lens with a strongly concave surface facing the image side, a concave lens with a strongly concave surface facing the object side, and a cemented lens of a biconvex lens and a biconcave lens, and the focal length of a part of the variator is f2s.
A telephoto zoom lens that satisfies the conditional expression: (+15< processing 2, where fa is the focal length of the cemented lens of a part of the variator. 2. Focusing having positive refractive power in order from the object side. a first group as a variator section, a second group as a variator section that has a negative refractive power and mainly converts the focal length by moving on the optical axis, and a second group that has a positive refractive power and that mainly converts the focal length by moving on the optical axis. A zoom lens consisting of a variable power system consisting of a third group as a part of a compensator that maintains the image plane at a predetermined position, which changes due to the movement of a part of the variator, and a relay lens system that follows the variable power system. The variator section consists of, in order from the object side, a concave lens with a strongly concave surface facing the image side, a concave lens with a strongly concave surface facing the object side, and a cemented lens of a biconvex lens and a biconcave lens. consists of, in order from the object side, a convex lens P, a cemented convex lens with a concave lens N1, and a cemented convex lens with a convex lens P2 and a concave lens N2,
The relay lens system is composed of, in order from the object side, a front group as a cemented convex lens consisting of a concave lens P3 and a concave lens N5, and a rear group consisting of a concave lens with a strongly concave surface facing the object side and a biconvex lens, and the focal point of the variator section is When the distance is f2, the focal length of the cemented lens of the variator part is fa, the Atsube number ν and the partial dispersion ratio θ, the convex lenses P+, P2 and P5 forming the front group of the compensator part and the relay lens system. The Abbe number and partial dispersion ratio of N1°N2 and N5 are νN, similarly to θP1. When θ・N, +21 (0,6469-0,001755shiP)〈
θP(3) θN < (0,646,9~0.00
A telephoto zoom lens, characterized in that it satisfies the following conditional expressions.