JPS6370817A - Single focus lens - Google Patents

Abstract

PURPOSE:To simplify a mechanism of the periphery of a lens system, and also, to obtain a video camera use single focus lens of a high performance, which is small in size, light in weight and low in cost, by an extremely small number of constituting pieces, by using a behind-diaphragm for a video camera use lens. CONSTITUTION:The single focus lens is constituted of a first group of a single lens having a negative refractive power, a second group of a single lens having a positive refractive power at a comparatively larger air interval than the first group, and a third group constituted of a negative single lens, and subsequently, two pieces of positive single lenses in order from an object side at a comparatively larger air interval than the first group, in order from the object side. In this state, conditions of the expression I through the irregurality V are satisfied. In this regard, (f), f1 and f3, and f1.2, and d2, and d4 denote a focal distance of the whole system, focal distances of the first group and the third group, a composite focal distance of the first group and the second group, an air interval between the first group and the second group, and an air interval between the second group and the third group, respectively. In this way, a small size, a light weight, a low cost, and an excellent aberration correction can be realized by a small number of lens pieces.

Description

[Detailed Description of the Invention] Industrial Field of Application The present invention relates to a high-performance single focus lens that is suitable for use in video cameras, is compact, lightweight, and low-cost, and has a reduced number of lenses. .

Conventional technology Recent video cameras place emphasis on operability and mobility, and in response to this demand, imaging devices have also been developed with 1 and 27 mm.
(1/2 inch) small size is becoming mainstream. In addition, while there is a demand for a zoom lens with a large aperture ratio, high magnification, small size and light weight, and high performance, there is also a need for a small, light, and low-cost single focus lens that is easy to handle, does not have a complicated cam mechanism, and has a small number of components. There is a strong pressing need to realize this lens. Most conventional video camera lenses are zoom lenses, and when the zoom ratio is around 6, the number of elements is 13 to 15 in 4 groups, and the aperture of the lens is large in order to secure the F number on the long focal length side. There is a limit to how small and lightweight it can be made. Also, in the case of a zoom lens, multiple lens groups move to change the magnification, and to achieve this, a complicated cam mechanism and lens drive means are required. is necessary, and there is a limit to cost reduction.In the case of single-focal-length lenses, due to constraints from the image sensor, the exit pupil of the lens system must be lengthened to prevent color shading, which results in a large number of lenses. Furthermore, since the diaphragm is included in the lens system, the lens barrel must be separated, resulting in increased costs.

Problems to be Solved by the Invention The present invention uses a behind-the-scenes diaphragm in a video camera lens, thereby simplifying the mechanism around the lens system and producing a compact, lightweight, low-cost, high-performance video camera with an extremely small number of components. The present invention provides single focus lenses for cameras.

Means for Solving the Problems The configuration of the single focus lens of the present invention includes, in order from the object side, a first group of single lenses having a negative refractive power, and a single lens having a positive refractive power separated by a relatively larger air distance than the first group. a second group of single lenses having a refractive power of It consists of a group and satisfies the following conditions.

+ll 1. of<lr, l<1.5f(21f,
・2>rlo, 25 f1 ・2<-r7o, oa (3) 0.43f<d2<0.631 +41 1.25f<f8<1.65f (sl 0.
4or<d4<o, aor, where f is the focal length of the entire system, i, r3 are the focal lengths of the first group and the third group, respectively.
fl.2 represents the combined focal length of the first and second groups, d2 represents the air distance between the first and second groups, and d4 represents the air distance between the second and third groups.

Operation The present invention achieves compactness, light weight, low cost, and excellent aberration correction with an unprecedentedly small number of lenses, 5, by using the above-mentioned configuration, that is, by utilizing the behind aperture and selecting appropriate lens types and lens materials. It is something.

EXAMPLE Hereinafter, an example of the single focus lens of the present invention will be described with reference to the drawings.

FIG. 1 shows a configuration diagram of an embodiment of a single focus lens of the present invention. In Fig. 1, 1 is the first group, 2 is the second group, 3 is the third group, 4 is the aperture, and 5 is an equivalent glass plate corresponding to a crystal filter or a face plate of an imaging device. .

When configuring a single focus lens for a video camera with a behind aperture, the position π of the exit pupil of the lens system is almost close to the aperture position, so in order to avoid color shading, the back focus must be set at 1.5 to 2 points of the focal length. It is necessary to make it as long as .0 times. In order to be compact and have a long back focus, the decisive factor is to increase the power of the first group 1. The 0 condition + 1) gives strong power, but the balance due to the shape of each group reduces aberrations. This is within the range that can be achieved. When it deviates from the lower limit, it can be made compact, but since the angle of incidence of the axial rays on the second group 2 increases, the radius of curvature of some surfaces after the second group becomes small, making it difficult to correct aberrations.

If the upper limit is exceeded, aberrations can be easily corrected, but the back focus becomes short, which is not preferable.

Condition (2) is a condition that indirectly defines the power of the second group 2. If the lower limit is exceeded, the back focus will become shorter,
The necessary exit pupil position cannot be secured.

When the upper limit is exceeded, the power and ray height of the third group 3 become too large, making it impossible to maintain good aberrations.

Condition (3) is combined with condition (1) and condition (2) to form the first group l.
This is to define an appropriate distance between the lens and the second group 2 and obtain the necessary back focus. If the upper limit is exceeded, the back focus will become longer, but the entire lens system will become longer, which is not preferable. If the lower limit is exceeded, the bank focus becomes too short and the necessary exit pupil position cannot be secured.

Condition (4) is also related to condition (2), but if the lower limit is exceeded, the curvature of each surface of the third group becomes steeper, causing higher-order spherical aberration and coma, making it difficult to correct aberrations. Exceeding the upper limit is advantageous for correcting aberrations, but is not preferable because securing the F number increases the length of the entire lens system.

Condition (5) is a range in which good chromatic aberration and Seidel aberration can be achieved. If d exceeds the lower limit, the height of the off-axis rays incident on the third group 3 becomes low, making it difficult to correct the chromatic aberration of magnification. If the upper limit is exceeded, the ray height of off-axis rays incident on the third group increases, making it difficult to correct coma aberration.

The aperture is placed immediately after the third group. Therefore, the structure of the lens barrel becomes very simple and costs can be reduced.

Under the lens configuration and conditions based on the present invention, a compact and high-performance single focus lens for a video camera with an F number of approximately 1.6 could be realized with a five-element configuration.

Examples satisfying these conditions are r1 in Table 0 below.
r2... is the radius of curvature of each surface of the lens, counted casually from the object side, d,, d2... is the wall thickness or air gap between the lens surfaces, n l, n 2...
is the refractive index of each lens for the d-line; C2...
... is the Atsbe number for d green.

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Figures 3, 4, 5, and 6 are for Example 1. Example 2. Example 3. From Figure 0 showing the aberration performance of Example 4 and Example 5, it can be seen that each example exhibits good optical performance.

Effects of the Invention As is clear from the above explanation, under the lens configuration and conditions of the present invention, a compact and high-performance single focus lens with an F number of approximately 1.6 was created using a very small number of lenses, 5. .

[Brief explanation of the drawing]

Fig. 1 is a configuration diagram of a single focus lens according to an embodiment of the present invention, Fig. 2 is a diagram of various aberrations of embodiment 1, Fig. 3 is a diagram of various aberrations of embodiment 2, and Fig. 4 is a diagram of various aberrations of embodiment 3. FIG. 5 is a diagram of various aberrations of Example 4, and FIG. 6 is a diagram of various aberrations of Example 5. 1...First group, 2...Second group, 3...
...3rd freshness, 4...aperture, 5...
A dummy glass corresponding to a crystal filter, etc. In the diagram of spherical aberration, the solid line is the d-line, the dashed line is the spherical aberration for the g-line, and the diagram of astigmatism, the solid line is the sagittal curvature of field, and the dotted line is the meridional curvature of field. Name of agent: Patent attorney Toshio Nakao 1 person / -$1
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Claims (1)

[Scope of Claims] (1) In order from the object side, a first group of single lenses having negative refractive power, and a single lens group having positive refractive power separated by a relatively larger air distance than the first group. It consists of a second group, and a third group consisting of a negative single lens in order from the object side with a relatively larger air distance than the first group, followed by two positive single lenses, and under the following conditions. A single focal length lens that satisfies the following. (1) 1.0f<|f_1|<1.5f (2) f_1・_2>f>0.25 f_1・_2<-f/0.08 (3) 0.43f<d_2<0.63f (4 )1.25f<f_3<1.65f (5) 0.40f<d_4<0.80f However, f is the focal length of the entire system, f_1 and f_3 are the focal lengths of the first group and the third group, respectively, f_1・_2 is the combined focal length of the first group and the second group, d_2 is the air distance between the first group and the second group, and d_4 is the air distance between the second group and the third group. (2) A single focus lens according to claim (1), wherein the diaphragm is disposed between the final lens surface of the third group and the image plane.