JP2008035199A - Imaging device having optical filter means - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain an imaging device having an optical filter means capable of changing a spectral characteristic in accordance with the brightness of a subject with a wide dynamic range and capable of taking an image.
An image pickup apparatus having an image pickup element and an optical filter means for selectively inserting and removing a plurality of optical elements in an optical path of light from a photographing optical system to the image pickup element. The plurality of optical elements include a hybrid infrared cut filter L2 having both an infrared cut action and an ND action, and the optical filter means drives the plurality of optical elements with one drive means.
[Selection] Figure 1

Description

  The present invention relates to an imaging apparatus having optical filter means, and is suitable for a digital still camera, a video camera, a surveillance camera, and the like on which various optical filters such as an infrared cut filter and an ND filter are mounted.

  The exposure sensitivity area of an image sensor such as a CCD is narrower than that of a silver salt film. For this reason, conventionally, in an imaging apparatus using an imaging element such as a CCD, a wide exposure dynamic range has been performed using a mechanism for inserting and removing an ND filter from an optical path in accordance with the brightness of a subject (Patent Literature). 1, 2).

  In many imaging apparatuses, an infrared cut filter for cutting near infrared light, which is harmful light for obtaining a color image, is arranged on the light incident side of the imaging element.

  When an infrared cut filter is used, the amount of light incident on the image sensor is reduced. For this reason, when the subject is dark, at the expense of the color balance of the color image, the infrared cut filter is retracted from the optical path so that a large amount of light enters the image sensor.

There is known an imaging apparatus that secures a sufficient amount of light and enables photographing in a dark place to widen the dynamic range (Patent Documents 3 and 4).
JP-A-10-90748 JP 2000-122109 A JP 11-98390 A JP 2002-189238 A

  The conventional imaging apparatus has an infrared cut filter and an ND filter in order to have a wide dynamic range and change the spectral characteristics according to the brightness of the subject.

  And it had separately the drive means which inserts / removes an infrared cut filter from an optical path, and the drive means which inserts / detaches an ND filter from an optical path. For this reason, two driving means and their arrangement spaces are required, and the entire apparatus tends to be complicated.

  The present invention can perform insertion / removal from / to the optical path of any one of the plurality of optical filters with a simple driving means, and changes the spectral characteristics according to the brightness of the subject with a wide dynamic range, An object of the present invention is to provide an imaging device capable of photographing.

An image pickup apparatus having the optical filter means of the present invention,
An imaging device having an imaging filter and optical filter means for selectively inserting and removing a plurality of optical elements in an optical path of light from the imaging optical system to the imaging element,
The plurality of optical elements include a hybrid infrared cut filter having both an infrared cut action and an ND action.
The optical filter means drives the plurality of optical elements with a single driving means.

  According to the present invention, it is possible to perform insertion / removal of a hybrid infrared cut filter having an infrared cut action and an ND action in accordance with the amount of subject light with a single drive unit. Furthermore, according to the present invention, it is possible to achieve an imaging apparatus having an optical filter means that can reduce the size of the entire apparatus while ensuring a wide dynamic range during shooting.

  Embodiments of the present invention will be described below with reference to the drawings.

  FIG. 1 is a schematic diagram of a main part of a first embodiment of an imaging apparatus such as a digital camera or a video camera having the optical filter device of the present invention.

  In FIG. 1, reference numeral 10 denotes a photographing optical system that guides light (photographing light) from a subject to an image sensor, and includes a lens portion L1, an aperture stop (iris stop) SP, and a lens portion L2. The photographing optical system 10 is a photographing lens or zoom lens having a single focal length, and is disposed on the object side (light incident side) of the image pickup device 21 described later.

  Reference numeral 20 denotes an optical filter means. The optical filter means 20 has a plurality of optical filters (optical elements) L1, L2, and L3. L1 is an infrared cut filter having an infrared cut action, L2 is a hybrid infrared cut filter having an infrared cut action and an ND action, and L3 is a parallel flat plate transparent in the visible range and the infrared range. L3 is a transparent parallel plate (glass plate) that is inserted into the optical path when neither infrared light nor visible light is cut, so that the optical path length does not change from when the optical filters L1 and L2 are inserted. An optical element for adjusting the optical path length.

  The optical filter (optical element) included in the optical filter means 20 is not limited to the above, and may be a low-pass filter, a color filter, a color temperature conversion filter, or the like. However, the plurality of optical filters (optical elements) of the optical filter means 20 are desirably a plurality of optical filters having different optical characteristics.

  Reference numeral 21 denotes an image sensor, and 22 denotes a part of driving means of the optical filter means (of course, it may be different from the optical filter means). Here, the optical filter means 20 is reciprocated in the direction of the arrow so that one of the optical filter means 20 is selectively disposed in the optical path of the photographing optical system 10. Incidentally, it is desirable that the “one drive means” mentioned here is one motor. However, a plurality of motors that perform substantially the same function in order to move one member (the filter holding frame 23 in this embodiment), rotate one shaft, or rotate one turret. It does not matter.

  In this embodiment, an infrared cut filter having an infrared cut action and a hybrid infrared cut filter having another wavelength characteristic in addition to the infrared cut action are driven by one drive means (motor, etc.). ing. In the present embodiment, another wavelength characteristic of the hybrid infrared cut filter is an ND action that can reduce the transmittance uniformly in the visible wavelength range.

  FIG. 2 is an explanatory diagram of the spectral characteristics of the filters L1, L2, and L3 shown in FIG. A curve SL1 is a spectral characteristic of the infrared cut filter L1. A curve SL2 is a spectral characteristic of the hybrid infrared cut filter L2. A curve L3 is a spectral characteristic of the optical filter L3.

  Here, the infrared cut action means that the transmittance at a wavelength of 400 nm to 620 nm is 90% or more and the transmittance at a wavelength of 720 nm to 900 nm is 1% or less.

  Such an infrared cut action has a multilayer film in which thin films are laminated.

  The ND action is an optical action that uniformly reduces the transmittance at a wavelength of 400 nm to 700 nm (difference in transmittance is within 15%, preferably within 10%). As a filter having an ND action, there is a so-called Newweight Density filter (gray filter).

  3 and 4 are schematic views of a hybrid infrared cut filter L2 according to the present invention. FIG. 3 shows an infrared cut filter and an ND filter bonded together, and FIG. 4 shows an infrared cut filter and an ND filter as one unit.

The hybrid infrared cut filter L2 in FIG. 4 has a structure in which an infrared cut filter (optical member) having an infrared cut action is doped with a metal element (Cu, Ti) in order to give an ND effect, or TiO, TiO ₂ , ZnO. A dielectric film containing an absorbing component such as ₂ is deposited. The infrared cut filter referred to here is an optical member that transmits visible light and absorbs or reflects infrared light.

  FIG. 5 is a schematic view of the main part of the optical filter means 20 of FIG. The optical filter means 20 is configured by linearly arranging a hybrid infrared cut filter L2, an infrared cut filter L1, and an optical filter L3 on a filter holding frame 23.

  FIG. 5 shows a case where the hybrid infrared cut filter L2 is positioned on the optical axis 10a of the photographing optical system 10.

  In this embodiment, when photographing a subject in a normal visible light region, the optical filter means 20 is driven by the drive means 22 so that the infrared cut filter L1 is positioned in the optical path. That is, the infrared light that is harmful light is cut so that the infrared light does not enter the image sensor 21.

  When the illuminance (luminance) on the subject side is very large (bright), the hybrid infrared cut filter L2 is positioned in the optical path. This cuts infrared light, limits the amount of visible light transmitted by the ND effect, and limits the amount of incident light incident on the image sensor 21. At this time, since the infrared cut filter effect is also provided, the color balance of the subject image obtained by the image sensor 21 does not change.

  When the illuminance on the subject side is very small and dark, the optical filter L3 is positioned in the optical path. At this time, infrared rays are incident on the image pickup device 21 and the color balance is slightly reduced, but the subject image can be projected sharply.

  Each filter in the present embodiment may be provided with an antireflection coating for preventing surface reflection, and according to this, higher optical performance can be exhibited.

  As described above, according to the present embodiment, the hybrid infrared cut filter having the infrared cut function and the ND function can be inserted and removed according to the amount of light of the subject with one drive means, and a wide dynamic range at the time of photographing can be obtained. The entire apparatus can be reduced in size while ensuring.

  In this embodiment, the image pickup device 21, the optical filter means 20, and the drive means 22 are components of the image pickup apparatus main body (camera main body), but the photographing optical system 10 is not necessarily a component of the image pickup apparatus main body. It doesn't have to be. That is, the photographic optical system 10 may be configured to be detachable from the imaging apparatus main body.

  FIG. 6 is a schematic view of the essential portions of Embodiment 2 of the photographing apparatus having the optical filter means of the present invention. The points not particularly described are the same as those in the first embodiment.

  The zoom lens ZL in FIG. 6 includes, in order from the object side to the image side, a first lens unit B1 having a negative refractive power, a second lens unit B2 having a negative refractive power, an aperture stop SP, and a third lens having a positive refractive power. The lens unit includes a group B3 and a fourth lens unit B4 having a positive refractive power.

  For zooming from the wide-angle end to the telephoto end, the second lens unit B2 is moved to the image side, and the third lens unit B3 is moved to the object side.

  Reference numeral 20 denotes an optical filter means, which has the same configuration as shown in FIG. Reference numeral 21 denotes an image sensor.

  Also in this embodiment, one of the optical filter means 20 is selected, and the selected one filter is inserted into and removed from the zoom lens ZL by one drive means 22.

1 is a schematic diagram of a main part of a first embodiment of a photographing apparatus having an optical filter means of the present invention. Illustration of spectral characteristics of each filter according to the present invention Configuration diagram of hybrid infrared cut filter according to the present invention Configuration diagram of hybrid infrared cut filter according to the present invention Configuration diagram of hybrid infrared cut filter unit according to the present invention Schematic view of the essential portions of Embodiment 2 of a photographing apparatus having the optical filter means of the present invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Image | photographing optical system 20 Optical filter means 21 Image pick-up element 22 Drive means 23 Filter holding frame L1 Infrared cut filter L2 Hybrid infrared cut filter L3 Optical filter ZL Zoom lens B1-B4: 1st-4th lens group SP: Aperture device

Claims (6)

An imaging device having an imaging filter and optical filter means for selectively inserting and removing a plurality of optical elements in an optical path of light from the imaging optical system to the imaging element,
The plurality of optical elements include a hybrid infrared cut filter having both an infrared cut action and an ND action.
The optical filter means drives the plurality of optical elements with a single drive means. The plurality of optical elements include an infrared cut filter,
The imaging apparatus according to claim 1, wherein the hybrid infrared cut filter and the infrared cut filter are inserted into and removed from the optical path by the one driving unit.   The imaging apparatus according to claim 1, wherein the plurality of optical elements include an optical element made of a transparent parallel plate. The hybrid infrared cut filter is obtained by doping an optical member having an infrared cut action with a metal element or by depositing a dielectric film containing at least one of TiO, TiO ₂ and ZnO _2. An imaging apparatus comprising the optical filter means according to any one of claims 1 to 3.   The imaging apparatus according to claim 1, wherein the imaging apparatus includes a photographing optical system that guides light from a subject to the imaging element. An image sensor, an optical filter means including a plurality of optical filters positioned on the light incident side of the image sensor, and one optical filter of the plurality of optical filters of the optical filter means on the light incident surface of the image sensor An image pickup apparatus having an optical filter means having one drive means inserted into and removed from
The optical filter means has a hybrid infrared cut filter having an infrared cut action and an ND action, and an image pickup apparatus having an optical filter means.