JP2003344761A - Shooting lens - Google Patents

Abstract

(57) [Summary] [Problem] To obtain a high-performance and compact photographing lens. In an imaging optical system using a solid-state imaging device, an imaging lens group (L1 to L5) including a plurality of lenses is provided on an object side of the solid-state imaging device, and an infrared absorption filter (IR) is used as an imaging lens group. By arranging it on the object side of the lens (L1) arranged closest to the object side,
Reduce the back focus of the photographing optical system. Further, an optical low-pass filter (LP) was arranged between the solid-state imaging device and the imaging lens group.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention is mainly applied to CCDs (chars such as digital still cameras, surveillance cameras, PC cameras (imaging devices attached to personal computers)).
The present invention relates to a high-performance and compact photographing lens used in a small-sized image pickup device using an image pickup device such as a ged coupled device).

[0002]

2. Description of the Related Art In recent years, the rapid spread of general-purpose digital still cameras (hereinafter, DSC) has been remarkable.
Structurally, the DSC is an image pickup device that electrically captures a still image formed by a photographing lens by an image pickup device (hereinafter, CCD) other than CCD and records it in a built-in memory or a memory card. In the beginning, since the LCD monitor can be used as a finder for shooting and as a monitor for playing back the captured image, it has spread widely by appealing its immediacy and convenience compared to silver salt cameras,
On the other hand, the resolution of the captured image is lower than that of a silver salt camera,
It has been pointed out as a drawback. However, in that respect as well, due to the rapid spread, the large number of CCD pixels will be supplied at low cost, and DSC approaches the resolution of silver halide cameras within the range of resolution such as print size, which is also popular in terms of resolution. It was improved and commercialized with great momentum.

Turning to the taking lens of the conventional DSC, the CCD is used for capturing an image even though it has a high number of pixels, and thus it is structurally similar to the taking lens for VTR. However, in terms of required resolving power and image quality, higher performance is required, so that the structure is often complicated, and the size of the optical system is C
Even if the screen size of the CD is the same, the taking lens for DSC becomes larger than the taking lens for VTR. The outline of the features of the conventional DSC photographing lens will be listed below.

1. With high image quality, the number of CCD pixels has recently reached 3 million to 400.
Million pixels have been announced at DSC for the general public. VT
Since the screen size is different from the 350,000-pixel class image sensor used for R, direct comparison does not make much sense, but if the screen size is ignored, there is a difference of about 10 times. It will be a matter. That is, it is required for the taking lens,
It is considered that the accuracy (difficulty level) of aberration correction also has a difference of about this difference.

In order to increase the number of pixels of the CCD, generally, at present, a method of increasing the number of pixels by reducing the pixel pitch without increasing the screen size is taken.
For example, in a CCD recently announced for a digital still camera with a class of 1.3 million effective pixels, the pixel pitch is about 4.2 μm. Therefore, assuming that the minimum circle of confusion is twice the pixel pitch, it is 8.4 μm, and the minimum circle of confusion for a 35 mm format silver halide camera is approximately 33 μm.
Therefore, it can be said that the resolution required of the taking lens of a digital still camera is about four times that of a silver halide camera.

2. Image-side telecentricity is good.The image-side telecentricity means that the chief ray of the ray bundle for each image point becomes almost parallel to the optical axis after exiting the final surface of the optical system. Means to intersect almost vertically. In other words, the exit pupil position of the optical system is sufficiently away from the image plane. This is because the color filter on the CCD is located slightly away from the imaging surface,
This is because when entering from an oblique angle, the substantial aperture efficiency decreases (called shading). Especially, in recent high-sensitivity CCDs, many have a microlens array immediately in front of the imaging surface. In this case as well, if the exit pupils are not sufficiently separated from each other, the aperture efficiency will be reduced in the periphery.

3. A large back focus is required. In addition to the glass plate for protection due to the structure of the CCD and the space after that, a space for inserting some optical elements between the optical system of the taking lens and the CCD (back Focus) is needed. An optical low-pass filter (hereinafter, OLPF, LP) inserted for the purpose of preventing a moire phenomenon caused by the periodic structure of CCD.
In addition, an infrared absorption filter (IR) also inserted between the optical system and the CCD for the purpose of lowering the sensitivity of the phase plate (PP) and CCD in the infrared wavelength range to approach the relative visual sensitivity of the human eye. ) Is that.

As described above, the conventional DSC photographic lens has roughly three characteristics (conditions). And 3. In order to realize the item (1), it is the current situation that even a standard lens must select the retrofocus type.
This is a major obstacle to downsizing of the taking lens.

[0009]

In view of the above-mentioned circumstances,
In a photographic optical system using an image sensor, the back side of the image sensor is provided with a lens group including a plurality of imaging lenses on the object side of the image sensor, and an infrared absorption filter is disposed on the object side of the lens group. It is an object of the present invention to obtain a taking lens characterized by being compact and capable of being shortened.

[0010]

That is, according to the present invention, in an image pickup optical system using a solid-state image pickup device, an image pickup lens group consisting of a plurality of lenses is provided on the object side of the solid-state image pickup device, and an infrared absorption filter is provided. Is arranged closer to the object side than the lens arranged closest to the object side in the imaging lens group, whereby the back focus of the photographing optical system is shortened. Further, an optical low pass filter is arranged between the solid-state image sensor and the image pickup lens group.

[0011]

BEST MODE FOR CARRYING OUT THE INVENTION In the taking lens system of the present invention, the back focus is set short by arranging an infrared light absorption filter on the objective side of the taking lens in a taking optical system using an image pickup device such as a CCD. It is characterized by

A conventional example in which an infrared light absorption filter is arranged between a photographing lens and an image pickup device and a first design in which the infrared light absorption filter of the present invention is arranged on the most object side of the photographing lens.
Table 1 shows the comparison of the total length (TL) with that of the example. The total length on the optical axis of the conventional example is TL = 16.59 mm,
In the first example, the total length was TL = 15.76 mm. This difference of 0.83 mm is the effect according to the present invention, which proves that it has a great effect on downsizing of the taking lens.

In the first embodiment, a single focus lens is used for explanation, but the present invention is not limited to a single focus lens.

[Table 1]

Hereinafter, the description of the present invention will be supplemented by showing concrete numerical values for the conventional example and the first embodiment. In the tables and drawings, f is the focal length of the entire lens system, F _no is the F number, 2ω is the total angle of view of the lens, and TL is the lens located closest to the object side or the object side surface of the infrared absorption filter to the image plane. On the optical axis, b _f represents the back focus. The back focus b _f is an air-equivalent distance from the image side surface of the lens closest to the image surface to the image surface. Also, R
Is the radius of curvature, D is the lens thickness or lens spacing, and N _d is d
The refractive index of the line, ν _d , represents the Abbe number of the d line. Further, d, g, and C in the spherical aberration diagram are aberration curves at respective wavelengths, S in the astigmatism diagram is sagittal, and M is meridional.

In the conventional example, an optical low-pass filter LP, a phase plate PP, an infrared light absorption filter IR, and a cover glass CG of CCD are arranged between the lens closest to the image plane and the image plane. In the first embodiment, the infrared absorption filter IR is arranged closest to the object side, and the optical low-pass filter LP, the phase plate PP, and the cover glass CG of the CCD are provided between the lens closest to the image plane and the image plane. It is distributed.

As for the aspherical surface used in the conventional example and the first embodiment, as is well known, when the Z axis is taken in the optical axis direction and the Y axis is taken in the direction orthogonal to the optical axis, the aspherical surface formula: Z = ( Y ² / r) [1 + √ {1- (1 + K) (Y / r)
² }] + A · Y ⁴ + B · Y ⁶ + C · Y ⁸ + D · Y ¹⁰ +
A curved surface obtained by rotating the curve given by ... around the optical axis, giving a paraxial radius of curvature: r, a conic constant: K, and a higher-order aspherical coefficient: A, B, C, D Is defined. In the notation of the conic constant and the higher-order aspherical coefficient in the table, "E and the number following it" represent "the power of 10." For example, “E-4” means 10 ⁻⁴ , and this numerical value multiplies the immediately preceding numerical value.

[Conventional Example] Table 2 shows numerical values of the conventional example. 3 is a lens configuration diagram thereof, and FIG. 4 is a diagram of various aberrations thereof. The lens configuration is as follows: the first lens L1 which is the negative lens from the most object side, the aperture diaphragms S1 and S2 with an air gap, the second lens L2 which is a positive lens with an air gap, and the air gap. The third lens L3, which is a negative lens, the fourth lens L4, which is a positive lens, and the fifth lens L5, which is a positive lens, are arranged with a slight air space between them. A retrofocus type is provided in which the first lens L1 has a diverging action, and the second lens L2 to the fifth lens L5 behind the aperture stop S have a converging action.

[Table 2]

Example 1 First Example of Photographic Lens of the Present Invention
Numerical examples of the examples are shown in Table 3. 1 is a lens configuration diagram thereof, and FIG. 2 is various aberration diagrams thereof. The general structure of the lens has not changed except that the infrared light absorption filter is arranged closest to the object side.

[Table 3]

In this way, by comparing the data of the conventional example and the data of the first example, the taking lens of the present invention is substantially the same as the conventional example in terms of performance, and further miniaturization is achieved. I understand.

[0020]

According to the present invention, it is possible to provide a high-performance and compact photographing lens.

[Brief description of drawings]

FIG. 1 is a lens configuration diagram of a first embodiment of a compact taking lens according to the present invention.

FIG. 2 is a diagram showing various aberrations of the compact taking lens according to the first example.

FIG. 3 is a lens configuration diagram of a conventional taking lens.

FIG. 4 is a diagram showing various aberrations of a conventional taking lens.

[Explanation of symbols]

IR infrared absorption filter L1 to L5 lenses S1, S2 aperture stop

Claims (2)

[Claims] 1. A photographic optical system using a solid-state image sensor, comprising an image-capturing lens group including a plurality of lenses on the object side of the solid-state image sensor, wherein an infrared absorption filter is located closest to the object side of the image-capturing lens group. The photographic lens is characterized in that the back focus of the photographic optical system is shortened by arranging the lens closer to the object side than the lens disposed in the. 2. The photographic lens according to claim 1, further comprising an optical low-pass filter arranged between the solid-state image pickup element and the image pickup lens group.