JPS595844Y2 - Imaging optical system that allows light intensity adjustment over a wide range - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an imaging optical system capable of adjusting the light amount, which includes a light amount adjusting filter for adjusting the amount of light transmitted through the photographing lens in addition to the photographing lens diaphragm.

Conventionally, in high-sensitivity television camera systems, when the amount of light that passes through the photographic lens is too large even if the mechanical aperture blades are used to stop the aperture, a so-called attenuator is created by moving close to the aperture of the photographing lens in order to reduce the amount of transmitted light. A filter for adjusting the amount of transmitted light is arranged.

As a filter for adjusting the amount of light, it is necessary to replace several types of filters with different transmittances as necessary, or to use a silver halide photosensitive material, so that the transmittance of a small area occupying the center is lower than that of the surrounding areas. A method has been implemented in which a filter with a non-transmissive portion is prepared in the vicinity of the diaphragm.

However, in the case of a system in which several filters are replaced, not only is it time-consuming to install the filters, but there is also the problem that the image is interrupted and disappears when the filters are installed.

In addition, when using a filter made of silver salt photosensitive material for the part that blocks the amount of light, it is difficult to make the light-transmitting part completely transparent, or the light-blocking part reflects more incident light than absorbs it. These lenses have the disadvantage that flare caused by reflection of scattered light on the lens surface deteriorates the image.

The present invention aims to eliminate the above-mentioned drawbacks, and for this purpose, an optical element having a fine diffraction grating structure is provided near the diaphragm of the lens as a filter for reducing the amount of transmitted light, or near the optical axis of a lens element provided near the diaphragm. A diffraction grating structure is provided in the optical axis, and a portion of the incident light beam is diffracted by the diffraction grating, and transmitted by total internal reflection within the optical element or lens provided with the grating, thereby reducing the amount of light near the optical axis. .

It is also possible to guide a part of the diffracted light transmitted by this total reflection to the light receiving means and adjust the aperture according to the measured amount.

The present invention will be explained below according to the drawings.

FIG. 1 shows an optical element A according to the present invention, where 1 is glass;
It is better to use a flat plate made of transparent rigid material such as plastic.

2 is a three-dimensional structure phase type diffraction grating formed using a non-silver salt photosensitive material such as photopolymer or photoresist. 56-25652)
I proposed it.

Further, 3 is an exit window which has been subjected to diffusion treatment, and 4 is a light receiving element.

The optical element 1 is arranged perpendicular to the incident light beam 5, and the light beam incident on the diffraction grating 2 is diffracted by this grating.

FIG. 2 shows this state, in which the light beam incident on the diffraction grating 1 is diffracted into zero-order light 6, +1st-order light 7, and -1st-order light 8.

The diffraction angle θ in the case of normal incidence is expressed by equation (1).

θ=sin−” (table)・・・・・・(1)(However, λ
is the wavelength of light, and the shortest of the wavelengths used shall be selected.

Further, P is the pitch of the diffraction grating.

) On the other hand, the conditions for total reflection of the light rays within the optical element between the transparent rigid body 1 and the medium in which it is arranged are (2
) is given by the formula.

θ>si Kanae) (2) (where n is the refractive index of the rigid body, and n is the refractive index of the surrounding medium.

) Therefore, if the pitch of the diffraction grating satisfies P〈λ', 1
It becomes possible to transmit the second-order diffracted light by total reflection on the surfaces 1a and 1b.

That is, the light is divided into zero-order light, which is not affected by the image even if it passes through the grating, and l-order light, which is transmitted by total reflection, and the transmitted light is attenuated in the portion where the grating is provided.

The optical element shown in Fig. 2 is a case in which a transmission type grating is provided, but Fig. 3 is a case in which a reflection type diffraction grating is provided on a transparent rigid flat plate 1, and here, the zero-order light and the +1st-order light are A diffraction grating is created so that most of the luminous flux is split into light.

FIG. 4 shows the change in transmittance of this optical element, and the transmittance can be arbitrarily selected by changing the diffraction efficiency of a diffraction grating of a certain shape.

Note that, although it is desirable that the diffraction grating has a three-dimensional structure, the diffraction grating is not limited thereto and may have a planar structure.

An embodiment of the present invention will be described below.

In FIG. 5, 9 is a lens, 10 is an aperture, and 11 is an imaging system such as a three-color separation system and an imaging tube.

Further, A is the above-mentioned optical element.

Here, the shape of the diffraction grating 2 is preferably circular with the optical axis as the center, but it may be other shapes such as a polygon.

When the aperture is wide open, the light beam incident on the lens 9 sufficiently passes through the peripheral area where the diffraction grating is not arranged, so the optical element A functions only as a photometric element.

That is, the light beam diffracted by the diffraction grating 2 is transmitted through the transparent rigid plate 1 by total reflection and is incident on the light receiving element 4.

The light receiving element 4 is connected to a photometric circuit (not shown) and a display member, so that the amount of light can be checked.

Furthermore, when the diaphragm is narrowed down beyond the diffraction grating, the incident light beam passes through the grating addition section, so the light attenuation effect of the diffraction grating is activated, and the range of light intensity adjustment can be expanded compared to when only the diaphragm is provided.

FIG. 6 shows another embodiment, in which 12 is an element of a lens 9, which is provided with diffraction gratings 2a and 2b.

Here, the diffraction gratings 2a and 2b are arranged concentrically, and only the first-order diffracted light from the central diffraction grating 2a is guided to the light receiving element 4, while the diffraction light from the diffraction grating 2b is guided in other directions. It gets absorbed.

Further, 13 is a photometric circuit, and 14 is an aperture adjusting means.The aperture adjusting means 14 is operated in response to a signal from the photometric circuit to control the aperture diameter of the aperture 10.

As described above, according to the present invention, a part of the light beam incident on the diffraction grating on the optical element is removed to the outside by total reflection, and since scattering caused by the silver salt photosensitive material is eliminated, the occurrence of flare can be suppressed. This is a useful optical system that not only allows for photometry by guiding total reflected light to a light-receiving element.

[Brief explanation of the drawing]

FIG. 1 is a perspective view of an optical element used in the present invention. FIG. 2 is a cross-sectional view illustrating the behavior of light rays within the optical element. FIG. 3 is a sectional view showing another optical element. FIG. 4 is a diagram showing changes in transmittance of an optical element. 5 and 6 are cross-sectional views showing embodiments of the present invention, respectively. In the figure, 1 is a transparent rigid body, 2 is a diffraction grating, 3 is a light extraction window for measuring the amount of light, 4 is a light receiving element, 5 is incident light, 6 is zero-order diffracted light, 7 is +1st-order diffracted light, and 8 is -1st-order diffracted light. 9 is a lens, 10 is an aperture, and 12 is an element of the lens.

Claims (1)

[Scope of utility model registration request] In an imaging optical system capable of adjusting light amount, which includes a light amount adjustment filter near the aperture of the photographing lens for adjusting the amount of light transmitted through the photographing lens, in addition to the aperture of the photographing lens, the light amount adjustment filter adjusts the amount of light transmitted through the photographing lens. It is an optical element having a fine diffraction grating structure near the axis, or a photographing lens element constituting the photographing lens having a fine diffraction grating structure, and the diffracted light diffracted by the fine diffraction grating structure is transmitted to the optical element. Alternatively, an imaging optical system capable of adjusting the amount of light, characterized in that the light is totally reflected within a photographing lens element and directed outside the photographing lens system.