JP2605719B2 - Shooting lens - Google Patents

Description

Description: FIELD OF THE INVENTION The present invention relates to a photographic lens, and particularly to a video camera, an electronic camera, or the like, which discretely samples spatial image information using a solid-state image sensor, an image pickup tube, or the like to obtain image information. The present invention relates to an imaging lens having an optical low-pass filter function suitable for an imaging system to be obtained.

(Prior Art) In recent years, various imaging systems for obtaining image information by optically spatially sampling a subject image with a solid-state imaging device or an imaging tube in video cameras, electronic cameras, and the like have been developed.

In the spatial sampling process of the photographing system, there is a spatial frequency related to image information called a Nyquist limit, and the minimum resolution of a transmitted photographed image is determined in relation to a sampling frequency within the Nyquist limit.

The spatial sampling corresponds to a response characteristic determined by the imaging optical system of the imaging system and the aperture arrangement of the pixels. Among the spatial sampling, there is a problem that a high spatial frequency component exceeding the Nyquist limit affects a low frequency within the Nyquist limit, hinders correct information reproduction and causes generation of a false signal.

In order to solve the above-mentioned problem, a method of disposing an optical low-pass filter (hereinafter, referred to as "low-pass filter") utilizing a diffraction grating in a taking lens system is disclosed in Japanese Patent Publication No. 60-34742 and Japanese Patent Application Laid-Open No. 60-34742. It is proposed in, for example, JP-A-61-126532. The low-pass filter limits the high spatial frequency component of the subject, thereby suppressing generation of a false signal.

However, the insertion of the low-pass filter having a certain thickness into the photographing lens system is often subject to various mechanical restrictions in the manufacturing process.
Further, this type of low-pass filter cannot exert a sufficient effect if the cross-sectional area of the transmitted light beam is small. For this reason, it is desirable to place the light beam to be transmitted at a position where the cross-sectional area of the light beam can be maximized, but it is not always possible to arrange the light beam at such a position.

Further, in the case where a low-pass filter is attached to a photographing lens not provided with a low-pass filter in a production process, there is a problem that optical performance is generally significantly deteriorated.

(Problems to be Solved by the Invention) The present invention can exhibit a function as a low-pass filter at an arbitrary position of a photographing lens, and further secures a space for disposing the low-pass filter in the photographing lens in advance. It is an object of the present invention to provide a photographic lens having a simple configuration that does not need to be placed.

(Means for Solving the Problem) At least one of the lenses constituting the taking lens has a lattice pattern having a function as an optical low-pass filter.

(Embodiment) FIGS. 1A, 1B and 1C are schematic views showing an embodiment of the present invention. FIG. 1A is a cross-sectional view of a photographing lens.
FIG. 1B is a perspective view of a lens having the function of an optical low-pass filter in FIG. 1A, and FIG. 1C is an explanatory view showing a cross section of a part of the lens surface of the lens.

In FIG. 1A, reference numeral 1 denotes an aperture, and 2 denotes a lens having an optical low-pass filter function on at least one lens surface, and is made of, for example, a plastic material or a glass material.

2B and 2C, reference numeral 2 denotes the lens, and reference numeral 3 denotes a lattice-like concave / convex portion formed on the lens surface on the object side of the photographing lens 2. The lattice-like concave / convex portion serves as an optical low-pass filter. The function of is demonstrated. Reference numeral 4 denotes the optical axis of the lens 2, and reference numeral 5 denotes a normal curved surface state when the lens surface of the lens 2 is not formed with irregularities.

The lens 2 having the lattice-shaped irregularities is formed, for example, by casting.

The function of the optical low-pass filter of the present embodiment utilizes a phase change of a light beam passing through a lattice-shaped uneven portion.

In this embodiment, as shown in FIG. 1A, a lattice-shaped uneven portion having an optical low-pass filter function is provided on the lens surface near the stop of the taking lens where the pupil function changes. Thus, the lattice-shaped uneven portion gives a phase difference to the passing light beam, changes the phase term of the pupil function of the photographing lens, restricts a high spatial frequency component of the subject, and functions as a phase-type optical low-pass filter. Plays well.

FIG. 2 is a schematic view showing a lens provided with the function of an optical low-pass filter according to another embodiment of the present invention. FIG. 1 shows a lens equivalent to the lens 2 in the photographing lens of FIG. 1 (A).

In the same figure, reference numeral 2 denotes a lens, and 6 denotes a stripe-shaped thin film coating on the lens surface on the object side on the lens 2. The coating film is controlled by controlling the refractive index and the thickness of the coating film. The function as an optical low-pass filter is exerted by changing the phase difference between the light beam passing through the light beam and the light beam passing through other portions.

In particular, the coating film is also provided with a characteristic having a different reflectance depending on the wavelength of the incident light beam. For example, green light having a wavelength of about 550 nm has a relatively high sampling frequency, and red and blue have a low sampling frequency.In an image sensor that produces a luminance signal at the same frequency as the green light, the reflectance of 550 nm is reduced, and the low-pass By reducing the effect, a higher resolution luminance signal is obtained.

In addition, in the present embodiment, a grid-like light and shade pattern (not shown) similar to that shown in FIG. 2 is formed, and the function of an optical low-pass filter is exhibited by controlling the amount of light transmitted through the light and shade pattern. Let me.

At the same time, the light and shade pattern is provided with the characteristic that the transmittance varies depending on the wavelength of the incident light beam. For example, of the light flux incident on a light portion of the shading of the lens surface, about
The transmittance of blue and green light of relatively short wavelength of 580 μm or less is set to nearly 100%, and the transmittance of red and infrared light of relatively long wavelength of about 600 μm or more is set to near 0% for both dark and light parts. By doing so, it is possible to provide not only a function as an amplitude-type optical low-pass filter that limits high spatial frequency components of a subject, but also a function as a color filter that blocks infrared light.

The infrared light cutoff filter is generally used to block infrared light or the like in the long wavelength region because the imaging tube in the optical system of a color television camera generally has high spectral sensitivity in a long wavelength region. If a lens having an optical low-pass filter is used for the photographing lens of the color television camera as in the embodiment of FIG. 2, it is preferable because an infrared light cutoff filter does not need to be separately provided.

In the embodiment, the grating pattern of the coating film and the shading pattern applied to the lens surface are prepared with different periods, and they are exchanged as occasion demands. The frequency characteristics of the optical low-pass filter may be changed.

In the above-described embodiment, the pattern formed on the object-side lens surface of the lens 2 is a pattern on a lattice (striped shape) having periodicity in one direction, but the pattern is formed in a plurality of different directions. It may be a pattern having a shape having a property. In this case, one lens surface may be used, or a plurality of lens surfaces may be used.

When the pattern is divided into a plurality of lens surfaces, only one pattern having periodicity in one direction is applied to one lens surface, and each lens surface is mechanically relative to each other in order to maintain an optical low-pass filter effect. It is preferable that the angle formed by the direction of the period of the pattern on each lens surface does not substantially change.

Incidentally, if the configuration is such that the frequency characteristics in an arbitrary direction on the imaging surface do not change even if the plurality of lens surfaces rotate relatively, there is no problem even if each lens surface rotates.

In the above-described embodiment, the pattern applied to the lens surface is a lattice (striped shape) having a periodic structure. For example, a prism-shaped pattern proposed in Japanese Patent Application Laid-Open No. 61-254924 is used. It may have an amplitude transmittance equivalent to that of.

(Effects of the Invention) According to the present invention, a lattice-like (stripe-shaped) pattern having the function of an optical low-pass filter is applied to at least one lens surface of a photographic lens, so that the optical low-pass The optical low-pass filter can be freely placed in the position where the effect of the filter can be maximized, and there is no restriction on the mechanism that occurred when the optical low-pass filter was inserted into the shooting lens in the past, and the optical low-pass filter was installed Since a photographing system that has not been used can be easily used, the manufacturing process can be advantageously promoted. Further, the lattice-shaped (stripe-shaped) pattern has different characteristics of transmittance and reflectance depending on the wavelength of the incident light beam. By having, for example, it is possible to achieve a photographic lens that also has a function of a filter that restricts a light beam of a specific wavelength such as infrared light. it can.

[Brief description of the drawings]

1 (A), 1 (B) and 1 (C) are schematic views showing an embodiment of the present invention. FIG. 1 (A) is a sectional view of a taking lens, and FIG. 1 (B) is a function of an optical low-pass filter. (C) is an explanatory view showing a cross section of FIG. (B). FIG. 2 is a schematic view showing a lens surface according to another embodiment of the present invention. In the figure, 1 is an aperture, 2 is a lens having the function of an optical low-pass filter, 3 is a lattice-like unevenness, 4 is an optical axis, 5 is a lens surface of the lens 2, and 6 is a stripe-shaped coating film.

Claims (6)

(57) [Claims] 1. A photographic lens, wherein at least one of the lenses constituting the photographic lens has a lattice pattern having a function as an optical low-pass filter. 2. The lens provided with the lattice-shaped pattern is manufactured by casting plastic or glass, and the pattern is formed by forming a material having substantially the same quality as the material of the lens in an uneven shape. 2. The photographing lens according to claim 1, wherein: 3. The photographing lens according to claim 1, wherein said lattice-like pattern is a vapor-deposited film having a different reflectance depending on a wavelength. 4. The photographing lens according to claim 1, wherein said lattice-like pattern is a light and shade pattern having a transmittance different depending on a wavelength. 5. The photographic lens according to claim 1, wherein said lens provided with the lattice pattern blocks light having a predetermined wavelength. 6. The photographing lens according to claim 5, wherein the light having the predetermined wavelength is infrared light.