JP2000019392A - Photographing lens - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a compact, lightweight and inexpensive photographing lens loaded in a camera for inputting an image and a camera for monitoring. SOLUTION: This photographing lens is constituted of a 1st lens group 1 having negative refractive power, a 2nd glass lens 2 having positive refractive power and a 3rd plastic lens 3 having the positive refractive power in order from an object side. Then, the surface of the lens 3 on an image side is provided with a diffraction element for correcting chromatic aberration. Besides, the plastic lens of the group 1 is provided with the negative refractive power and the lens 3 is provided with the positive refractive power. Thus, the movement of focus caused by the change of temperature is reduced and excellent aberration performance and excellent MTF performance are obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a small and inexpensive photographing lens suitable for an image input camera, a surveillance camera, and the like.

[0002]

2. Description of the Related Art In recent years, with the spread of video cameras and personal computer input cameras, the size and weight of CCDs and peripheral ICs have been reduced. There is a strong demand.

Hereinafter, an example of a conventional photographing lens will be described with reference to the drawings. Conventionally, as a photographing lens, a single focus lens described in JP-A-9-113799, a low-magnification zoom lens described in JP-A-9-213326, and the like are known. FIG. 8 shows the photographing lens. FIG. 8 is a schematic view showing the configuration of a conventional photographing lens. In order from the object side, a negative lens group 1 composed of three or less lenses and two or three or four lenses in three groups including a cemented lens are shown. It comprises a positive lens group 2 and a dummy glass 3 having a thickness equivalent to that of a low-pass filter between the positive lens group 2 and the image plane 4.

The operation of the conventional photographic lens having the above-described configuration will be described below. In order to obtain a long back focus equivalent to the focal length, it is necessary to form the front lens unit as a negative lens unit and the rear lens unit as a positive lens unit.
In the positive lens group 2, mainly spherical aberration, lateral aberration and chromatic aberration are corrected.
This is to keep the aberration performance in good condition. The lens MTF performance is a spatial frequency of 53.4 lines / mm.
(Equivalent to 300 TV lines), the contrast is 70%, and the image height is about 30%, including the sagittal direction and the meridional direction, at the 7.5% point. In order to satisfy this performance, all are constituted by glass lenses, and a plurality of aspherical lenses and cemented lenses are used.

[0005]

However, the conventional configuration using a plurality of glass aspherical lenses or cemented lenses as described above is insufficient in terms of reducing the number of lenses, making it smaller, lighter and less expensive. Had.

The present invention solves the above-mentioned conventional problems, and uses a plastic aspheric lens which can be produced at a lower cost than a glass aspheric lens, and further uses two cemented lenses with one lens with a diffraction element. An object of the present invention is to provide a small, lightweight, and inexpensive photographing lens by reducing the number of photographing lenses.

[0007]

In order to achieve this object, a photographic lens according to the present invention comprises, in order from the object side, a first lens group having a negative refractive power and a second glass lens having a positive refractive power. And a third plastic lens having a positive refractive power. The first lens group includes one or two negative lenses, one of which is a plastic lens, and the second glass lens is The third plastic lens is composed of a positive lens having a double-sided aspherical surface, and the third plastic lens is a lens having an aspherical surface on the image side and a kinoform shape of a diffraction element.

With this configuration, focusing movement due to a temperature change peculiar to a plastic lens is suppressed, and a surface with a diffractive element capable of correcting chromatic aberration is provided in the same manner as a cemented lens. can get.

[0009]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The invention according to claim 1 of the present invention comprises, in order from the object side, a first lens group having a negative refractive power, a second glass lens having a positive refractive power, A first plastic lens having a refractive power;
The lens group is composed of one or two negative lenses, one of which is made of a plastic lens, the second glass lens is made of a positive lens having a double-sided aspherical shape,
The third plastic lens is a photographic lens having an image-side surface formed of a lens having a kinoform shape of a diffractive element on an aspherical surface. The first lens group mainly includes astigmatism and distortion. The second glass lens corrects mainly spherical aberration and coma, and the third plastic lens corrects mainly coma and astigmatism. Further, the third plastic lens has an effect of correcting axial chromatic aberration and chromatic aberration of magnification by the diffractive element on the image side of the third plastic lens.

According to a second aspect of the present invention, the negative plastic lens and the positive third plastic lens included in the first lens group satisfy the following conditions.

[0011]

(Equation 2)

2. A photographing lens according to claim 1, wherein said lens is arranged such that when the temperature rises, said lens is not satisfiable.
/ F1 increases and the focus position moves to the object side, but at the same time 1 / f2 decreases and the focus movement moves to the image side and is canceled. Conversely, when the temperature drops, 1 / f1
Becomes smaller and the focus position moves to the image side.
/ F2 increases, moves to the object side and is canceled,
However, if the above condition is not satisfied, the focus movement becomes large and has an effect of exceeding 1.0 μ / ° C.

Hereinafter, an embodiment of the present invention will be described with reference to FIG.
This will be described with reference to FIG. (Embodiment 1) FIG. 1 is a schematic view showing the configuration of a taking lens according to the present invention. In FIG. 1, reference numeral 1 denotes a first lens group having a single plastic lens, and reference numeral 2 denotes a second glass lens. Reference numeral 3 denotes a third plastic lens, and reference numeral 4 denotes a dummy glass having a thickness equivalent to that of a low-pass filter or the like located between the third plastic lens and the imaging surface 5.

Table 1 below shows examples of numerical values of the photographing lens constructed as described above. In Table 1, r1, r2... Are the radius of curvature of a reference spherical surface representing an aspherical shape corresponding to each lens surface counted in order from the object side, d1, d2. , N2... Are the refractive indices of each lens with respect to the d-line, .nu.1, .nu.2 are the Abbe numbers of each lens with respect to the d-line, .epsilon.1, .epsilon.2 are the eccentricities representing the aspherical shapes of the lens surfaces, and A1, A2. .. Are the sixth order aspherical surface coefficients of each lens surface, C1, C2... Are the eighth order aspherical surface coefficients of each lens surface, D
1, D2... Are the tenth order aspherical surface coefficients of the respective lens surfaces.

[0015]

[Table 1]

A photographing lens having the above configuration and having the numerical values as shown in Table 1 will be described below with reference to FIGS.

FIGS. 2 (a), (b), (c) and (d)
FIGS. 3A and 3B show aberration diagrams of the first embodiment, and FIGS. 3A and 3B show MTF characteristics diagrams of the first embodiment. However, aberration and MTF for the diffractive element on the last lens surface
The calculation uses a well-known method of a high refractive index method, and represents the performance of the diffracted primary light. FIG. 2 shows that excellent image performance is obtained by the optimal combination of the aspherical lenses. FIG. 3 shows that the MTF performance at a spatial frequency of 53.4 lines / line is 60% up to the periphery at the axial best position, indicating high resolution performance. For temperature compensation, the focal length of the plastic lens of the first lens group and the focal length of the third plastic lens satisfy the condition of (Equation 2).

As described above, according to the first embodiment, the diffractive element for correcting chromatic aberration and the negative and positive plastic lenses satisfying the condition (Equation 2) are provided on the final surface of the lens. Less focus shift due to temperature change,
An imaging lens having good aberration performance and high MTF performance can be obtained.

(Embodiment 2) FIG. 4 is a schematic diagram showing the configuration of a photographic lens of the present invention. 4, the first lens group 1, the second glass lens 2, the third plastic lens 3 and the dummy glass 4 have the same configuration as that of FIG. The difference from the configuration of FIG. 1 is that the first lens group is composed of two negative lenses, one of which is a plastic lens. This is an embodiment of a low-magnification zoom lens in which the distance between the first lens group and the second glass lens is made variable. Hereinafter, Table 2 shows examples of numerical values of this lens. The meaning of each symbol and the like in (Table 2) is the same as in (Table 1).

[0020]

[Table 2]

The difference between Table 2 and Table 1 is that the zoom lens has a focal length of 3.90 mm to 7.79 mm.

The photographic lens having the above configuration and having the numerical values as shown in Table 2 will be described below with reference to FIGS. 5A and 5B are aberration diagrams at the wide angle end and at the telephoto end of the second embodiment, respectively.
FIGS. 7A and 7B and FIGS. 7A and 7B show MTF characteristics at the wide angle end and the telephoto end according to the second embodiment. However, the aberration and the MTF of the diffraction element on the last surface of the lens are calculated using a high refractive index method, which is a well-known method, and represent the performance of the first-order diffracted light. FIG. 5 shows that good image performance is obtained at both the wide-angle end and the telephoto end. 6 and 7, the MTF performance at a spatial frequency of 53.4 lines / mm is 30% or more at the wide-angle end and the telephoto end at the axial best position, indicating that the device has excellent resolution performance. . As temperature compensation, the focal length of the plastic lens of the first lens group and the third plastic lens satisfy the condition of (Equation 2).

As described above, according to the present embodiment, a diffractive element for correcting chromatic aberration is provided on the final surface of the zoom lens, and the negative and positive plastics satisfying the condition (Equation 2) are also provided for the zoom lens. By providing the lens, it is possible to obtain good aberration performance and excellent MTF performance with less focus movement due to temperature change.

[0024]

As described above, according to the present invention, the first lens unit having a negative refractive power and the second lens unit having a positive refractive power are arranged in order from the object side.
In a taking lens composed of a glass lens and a third plastic lens having a positive refractive power, a diffractive element for correcting chromatic aberration is provided on the image-side surface of the third plastic lens.
By providing a negative refracting power to the plastic lens of the lens group and a positive refracting power to the third plastic lens, focus movement due to a temperature change is small, good aberration performance and excellent MT.
The effect of achieving F performance is obtained.

[Brief description of the drawings]

FIG. 1 is a schematic diagram illustrating a configuration of a photographing lens according to Embodiment 1 of the present invention.

FIG. 2 is an aberration diagram of a photographing lens according to the first embodiment.

FIG. 3 is an MTF characteristic diagram of the photographing lens according to the first embodiment.

FIG. 4 is a schematic diagram showing a configuration of a photographing lens according to Embodiment 2 of the present invention.

FIG. 5 is an aberration diagram of a photographing lens according to the second embodiment.

FIG. 6 is an MTF characteristic diagram of the photographing lens according to the second embodiment.

FIG. 7 is an MTF characteristic diagram of the photographing lens according to the second embodiment.

FIG. 8 is a schematic diagram showing a configuration of a conventional photographing lens.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 1st lens group 2 2nd glass lens 3 3rd plastic lens 4 dummy glass 5 imaging surface

 ──────────────────────────────────────────────────続 き Continued on the front page F term (reference) 2H087 KA01 LA01 PA03 PA04 PA17 PB03 PB04 QA02 QA06 QA17 QA21 QA22 QA25 QA32 QA41 QA45 QA46 RA05 RA12 RA13 RA32 RA36 RA42 RA43 RA46 SA07 SA09 SA62 SA63 SB03 SB13 UA01

Claims (2)

[Claims] 1. A first lens having a negative refractive power in order from an object side.
A lens group, a second glass lens having a positive refractive power, and a third plastic lens having a positive refractive power,
The first lens group includes one or two negative lenses, one of which is a plastic lens, and the second lens group includes a second lens.
A photographic lens, wherein the glass lens is a positive lens having a double-sided aspherical shape, and the third plastic lens is a lens having a kinoform shape of a diffraction element on an aspherical surface on the image side. 2. The negative plastic lens and the positive third plastic lens included in the first lens group satisfy the following conditions: The photographing lens according to claim 1, wherein the following condition is satisfied.