JPH1152234A - Tele-conversion lens - Google Patents

Abstract

PROBLEM TO BE SOLVED: To excellently compensate various aberrations, to suppress the generation of a ghost and to miniaturize a lens. SOLUTION: A tele-conversion lens TCL mounted on the image side of a master lens ML is composed of a front group of three lens constitution and a rear group of two lens constitution, either one group of the groups has a negative power, the front group is composed, from an object side, of a first lens having a negative power, a second lens having a negative power and a third lens having a negative power, the first and second lenses are separated from each other and the fourth lens and fifth lens of the rear group are made to a joined lens. In this case, the following conditions are satisfied: (1) 1.0<|f1.2.3|/|f|<2.0, (2) -0.1<e/|f|<0.3 and (3) ν5>ν4, where f1.2.3 is the composite focal distance of the first, second and third lenses, (f) is the focal distance of a whole teleconversion lens system, (e) is the interval of principal points between the first, second, third lenses and the fourth, fifth lenses, ν4 is an Abbe number of the fourth lens and ν5 is an Abbe number of the fifth lens.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a tele-conversion lens which is mounted on the image side of a master lens and extends its focal length.

[0002]

2. Description of the Related Art This type of tele-conversion lens has a negative power, and is prevented from interfering with the lens surfaces and the flare stopper when attached to the master lens, or due to other mechanical restrictions. It is common to be mounted away. Therefore, a teleconversion lens generally has a large negative power, and the Petzval sum tends to be a large negative value.

Conventionally, as a teleconversion lens which has improved such a point, a teleconversion lens as shown in Japanese Patent Publication No. 51-12421 is known. This means that the teleconversion lens consists of a front group with negative power and a rear group with positive power, and the principal point interval between the front group and the rear group is increased,
The negative power of the teleconversion lens is reduced by moving the principal point position of the entire system of the teleconversion lens toward the object side from the imaging position of the master lens alone.

[0004]

However, in such a conventional teleconversion lens, there is a problem that the symmetry of the entire lens structure is lost and coma aberration is easily generated. However, there is also a problem in that ghosts are easily generated because of the separation. The present invention has been made in view of the above points,
It is an object of the present invention to provide a compact tele-conversion lens capable of favorably correcting various aberrations and reducing ghosts.

[0005]

SUMMARY OF THE INVENTION In order to achieve the above object, the present invention provides a tele-conversion lens which is mounted on the image side of a telephoto master lens to increase the focal length thereof. It is composed of a group and a rear group composed of two sheets,
One of the groups has negative power, and the front group includes a first lens having negative power from the object side and the first lens.
The rear group includes a lens and a second lens having a positive power that is separate from the lens. The rear group is a cemented lens, and provides a tele-conversion lens that satisfies the following conditions. (1) 1.0 <| f1 · 2 | 3 | / | f | <2.0 (2) −0.1 <e / | f | <0.3 (3) ν5> ν4 where f1 · 2 * 3: Combined focal length of first, second, and third lenses f: focal point of the entire teleconversion lens e: principal point interval between first, second, third, and fourth and fifth lenses ν4: Abbe number of the fourth lens ν5: Abbe number of the fifth lens

In the above-mentioned tele conversion lens, it is preferable that the following conditions are satisfied. (4) 0.05 <Σd / | f | (5) | r3−r2 | / | f | <0.02 (6) n convex <1.62 1.65 <n concave where Σd: Length r2: radius of curvature of the second surface r3: radius of curvature of the third surface n convex: refractive index of convex lens n concave: refractive index of concave lens

[0007]

Embodiments of the present invention will be specifically described below with reference to the drawings. In general, a tele-conversion lens is attached to a telephoto lens that is large and bulky and heavy and is difficult to carry, and is often used to further extend the focal length of a master lens. It is most effective to use. Further, the telephoto lens has a long back focus, and there are few mechanical restrictions on bringing the teleconversion lens closer to the master lens.

Therefore, the teleconversion lens according to the present invention reduces the power of the teleconversion lens by bringing the teleconversion lens as close as possible to the master lens by limiting the master lens to the telephoto system, thereby reducing the Petzval sum and various factors. Along with minimizing aberrations, the height of the passing light beam is reduced to make the teleconversion lens more compact. Further, by separating the first lens and the second lens of the front group, various aberrations can be corrected well, and the ghost generated in the rear group can be suppressed by joining the two lenses of the rear group. did.

The lens system of the teleconversion lens according to the present invention includes a front lens group or a rear lens group having a negative power, and the front lens group includes a first lens having a negative power with a concave surface facing the image side; The rear group includes a second lens having a biconvex positive power and a third lens having a negative power.
The fourth lens composed of a convex lens and the fifth lens composed of a concave lens are cemented from the object side.

Then, the above-mentioned conditional expressions (1), (2),
By satisfying the condition (3), it is possible to satisfactorily correct various aberrations such as Petzval sum, coma aberration, chromatic aberration of magnification, and spherical aberration, thereby improving image quality.

In the conditional expression (1), if the value is below the lower limit of 1.0, the spherical aberration is deteriorated, and if the value is above the upper limit of 2.0, it becomes difficult to correct the Petzval sum. Also,
In conditional expression (2), if the value falls below the lower limit of -0.1, the Petzval sum becomes a negative value, and if the value exceeds the upper limit of 0.3, coma becomes worse. Furthermore, conditional expression (3)
Is related to the correction of the chromatic aberration of magnification. If the condition is not satisfied, it becomes difficult to correct the chromatic aberration of magnification.

If the above-mentioned conditional expressions (4), (5) and (6) are further satisfied in addition to the above-mentioned conditional expressions (1), (2) and (3), a teleconversion lens having better performance can be obtained. Obtainable. Conditional expression (4) defines the total length of the teleconversion lens with respect to the focal length f of the entire teleconversion lens system. This value is 0.0
When the value is less than 5, each power of the lens system becomes strong, and various aberrations including spherical aberration tend to be deteriorated.

Condition (5) defines the radius of curvature of the second and third surfaces by separating the first lens and the second lens of the front group. Accordingly, occurrence of higher-order aberrations can be prevented. Further, the conditional expression (6) defines the refractive index of the glass material used for the fourth and fifth lenses in the rear group. By satisfying this condition, it is possible to satisfactorily correct lateral chromatic aberration and Petzval's sum. it can.

It is desirable that the radius of curvature of the rear group satisfies the following expression in consideration of achromatism and astigmatism. 0.15 ≦ | r8 | / | f | ≦ 0.35 where r8 is the radius of curvature of the rear group junction surface

[0015]

Next, embodiments of the teleconversion lens according to the present invention will be described. FIGS. 1 to 4 are configuration diagrams showing Examples 1 to 4 together with the master lens ML.
FIG. 8 to FIG. 8 are aberration curve diagrams of Examples 1 to 4, respectively.

First, Table 1 shows a master lens to which the teleconversion lens is to be mounted.

[0017]

[Table 1] R1-12: radius of curvature of each surface of master lens ML D1-11: surface interval of each surface of ML N1-7: refractive index of each lens of ML ν1-7: Abbe number of each lens of ML

Next, the first to fourth embodiments of the tele-conversion lens mounted on the image side of the master lens ML as described above.
Are shown in Tables 2 to 5, respectively.

[0019]

[Table 2]

[0020]

[Table 3]

[0021]

[Table 4]

[0022]

[Table 5] Where, r1 to 9: radius of curvature of each surface of the teleconversion lens TCL d1 to 8: surface interval of each surface of TCL n1 to 5: refractive index of each lens of TCL ν1 to 5: Abbe number of each lens of TCL

[0023]

As described above, according to the first aspect of the present invention, the teleconversion lens according to the present invention satisfactorily corrects various aberrations including Petzval sum, coma aberration, chromatic aberration of magnification, and spherical aberration. Image quality can be improved. At the same time, by joining the two rear groups, it is possible to suppress ghosts occurring in the rear group.

According to the second aspect of the present invention, in addition to the above-mentioned effects, the generation of higher-order aberrations can be prevented, and a compact tele-conversion lens having better performance can be obtained.

[Brief description of the drawings]

FIG. 1 is a configuration diagram showing a first embodiment of the present invention together with a master lens.

FIG. 2 is a configuration diagram showing Embodiment 2 of the present invention together with a master lens.

FIG. 3 is a configuration diagram showing a third embodiment of the present invention together with a master lens.

FIG. 4 is a configuration diagram showing a fourth embodiment of the present invention together with a master lens.

FIG. 5 is an aberration curve diagram of the first embodiment.

FIG. 6 is an aberration curve diagram of the second embodiment.

FIG. 7 is an aberration curve diagram of the third embodiment.

FIG. 8 is an aberration curve diagram of the fourth embodiment.

[Explanation of symbols]

 TCL: Tele conversion lens ML: Master lens r1-9: Curvature radius of each surface of TCL d0: Surface space between ML and TCL d1-8: Surface space of each surface of TCL R1-12: Curvature radius of each surface of ML D1 11: Surface distance between ML surfaces SA: Spherical aberration AS: Astigmatism TC: Chromatic aberration of magnification

Claims (2)

[Claims] 1. A tele-conversion lens mounted on the image side of a telephoto master lens to increase the focal length thereof, comprising a front group having three lenses and a rear group having two lenses. One of the groups has negative power, the front group has a first lens having negative power from the object side, and a second lens having positive power separated from the first lens, The rear group is a cemented lens, which satisfies the following conditions. (1) 1.0 <| f1 · 2 | 3 | / | f | <2.0 (2) −0.1 <e / | f | <0.3 (3) ν5> ν4 where f1 · 2 * 3: Combined focal length of first, second, and third lenses f: focal point of the entire teleconversion lens e: principal point interval between first, second, third, and fourth and fifth lenses ν4: Abbe number of the fourth lens ν5: Abbe number of the fifth lens 2. The tele-conversion lens according to claim 1, wherein the following conditions are satisfied. (4) 0.05 <Σd / | f | (5) | r3−r2 | / | f | <0.02 (6) n convex <1.62 1.65 <n concave where Σd: Length r2: radius of curvature of the second surface r3: radius of curvature of the third surface n convex: refractive index of convex lens n concave: refractive index of concave lens