JP2005301155A - Optical filter - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To expand extent of light quantity control by an optical filter more than before. <P>SOLUTION: The optical filter having extinction action comprises a filter base 1, a 1st optical film 4A which is formed on the filter base and has a 1st gradation region 6, and a 2nd optical film 4B which is formed so that at least a part thereof is superposed on the 1st optical film in an optical axis direction and which has a 2nd gradation region 9. Further, end positions and length of the 1st gradation region and the 2nd gradation region 9 are made different from each other to change a changing ratio of transmissivity in a gradation extent. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to an optical filter called an ND filter or the like that is mainly used in an optical apparatus such as a video camera, a digital still camera, or an interchangeable lens device using an image sensor.

  In optical devices such as video cameras and digital cameras, the so-called "higher pixel" that increases the number of pixels while maintaining the size of the image sensor keeps both the improvement of the definition of the image obtained and the size reduction. . However, if the pixel pitch of the image sensor becomes shorter due to “higher pixels”, image degradation is likely to occur due to light diffraction when the aperture device is in the small aperture state.

  Specifically, if the aperture value is controlled (aperture control) in the aperture device so that this image deterioration does not occur, only about 3 to 4 stages of the EV value are used for the control. For example, in the case of a lens having an open F value of 2, the diaphragm can be operated only from 2 to 5.6 or from about 2 to 8, and if a smaller diaphragm than that is used, image degradation due to diffraction occurs.

  Therefore, in digital cameras, methods such as increasing the shutter speed on the high speed side of the mechanical shutter are also adopted, but there are mechanical limitations, and in order to obtain a desired shutter speed, the torque of the actuator is increased. Accompanying an increase in size.

  In addition, in an optical apparatus capable of shooting a moving image such as a video camera, a mechanical shutter cannot be used, and an electronic shutter speed for controlling a charge accumulation time can be controlled. It also has the disadvantage that it appears to move and cannot be seen as a natural motion as a moving image.

  Therefore, a light amount adjusting device used in an optical apparatus such as a video camera or a digital camera uses an optical filter having a dimming action called an ND filter to suppress image deterioration due to a diffraction phenomenon in a small aperture state. Yes.

  As such an ND filter, there has been proposed a multi-density ND filter having a plurality of density regions such that the transmittance increases in order toward the inside of the aperture opening (see Patent Document 1). A so-called gradation ND filter in which the density changes continuously has also been proposed (see Patent Document 2).

Furthermore, various exposure control methods have been proposed in which the control of the diaphragm blades and the ND filter having a plurality of densities and the control of the shutter speed are combined (see Patent Document 3).
JP-A-2-190833 (page 2, upper right column, line 9 to lower left column, line 15; FIGS. 1 and 2) Japanese Patent Laid-Open No. 5-281593 (paragraphs 0031, 0045 to 0048, FIGS. 4 to 12) JP 2000-214514 A (paragraphs 0064-0067, 0078-0097, FIGS. 1, 4-7)

  However, even in exposure (light quantity) control using a conventional gradation or multi-density ND filter, the change range of the transmittance of the ND filter is about four EV values. Therefore, like the aperture device, the number of controllable steps is limited for a wide range of subject brightness, and it is difficult to obtain good images for subjects with various brightnesses.

  An object of the present invention is to provide an optical filter and an optical apparatus using the same that can expand the range of light amount control as compared with the conventional one.

  In order to achieve the above object, according to one aspect of the present invention, there is provided an optical filter having a dimming function, a first optical element having a first gradation region formed on the filter base and the filter base. A film, and a second optical film that is formed so as to at least partially overlap the first optical film in the optical axis direction and has a second gradation region.

  According to the present invention, by combining the first and second optical films each having a gradation region, the range of light amount control that can be performed with only one optical filter and the degree of freedom in setting the light transmittance are conventionally achieved. Can also be enlarged. In particular, in the in-plane direction of the filter base, the positions of at least one of the both ends of the first gradation region and the second gradation region are different from each other, or the lengths of the first gradation region and the second gradation region are different. By making the first and second gradation regions different from each other in the optical axis direction, various light transmittance variation forms can be obtained.

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

  FIGS. 10A and 10B show the configuration of the lens barrel of a video camera (optical apparatus) provided with a gradation ND filter that is an embodiment of the present invention. In addition, FIG. 10B has shown the AA sectional view in FIG. 10A.

  In this embodiment, a zoom lens composed of four lens units, which are most commonly used in a video camera, in order from the object side, is composed of a fixed convex, a movable concave, a fixed convex, and a movable convex. ing.

  The four lens units constituting the zoom lens include a fixed front lens 201a, a variator lens 201b that performs a zooming operation by moving along the optical axis, a fixed afocal lens 201c, a light It is composed of a focusing lens 201d that moves along the axis to maintain the focal plane during zooming and perform focusing. Further, the ND unit 252 is fixed and disposed between the variator lens 201b and the afocal lens 201c. The ND unit 252 is provided with a gradation ND filter according to the present embodiment, which will be described later. The gradation ND filter is driven by an ND drive source 250 such as a stepping motor, thereby fixing a fixed aperture diameter (open diameter). It is possible to change the area covering the.

  The video camera of this embodiment is not equipped with a diaphragm device that adjusts the amount of light by driving the diaphragm blades and changing the aperture of the diaphragm.

  Guide bars 203, 204a, and 204b are arranged in parallel with the optical axis 205, and guide and prevent rotation of the moving lens. The DC motor 206 serves as a driving source for moving the variator lens 201b.

  The front lens 201 a is held by the front lens barrel 202, and the variator lens 201 b is held by the V moving ring 211. The afocal lens 201c is held by the intermediate frame 215, and the focusing lens 201d is held by the RR moving ring 214.

  The front lens barrel 202 is positioned and fixed to the rear lens barrel 216, the guide bar 203 is positioned and supported by both the lens barrels 202 and 216, and the guide screw shaft 208 is rotatably supported. The guide screw shaft 208 is rotationally driven by the rotation of the output shaft 206 a of the DC motor 206 being transmitted via the gear train 207.

  The V moving ring 211 that holds the variator lens 201 b includes a pressing spring 209 and a ball 210 that engages with a screw groove 208 a formed in the guide screw shaft 208 by the force of the pressing spring 209, and a DC motor 206. As a result, the guide screw shaft 208 is driven to rotate, so that the guide bar 203 moves forward and backward in the optical axis direction while being guided and restricted by the guide bar 203. As a driving source for the variator lens 201b, a stepping motor, a vibration type actuator using a piezoelectric effect, an electrostatic actuator, or the like may be used in addition to the DC motor.

  The guide bars 204a and 204b are supported by the rear barrel 216 and the intermediate frame 215 positioned on the rear barrel 216. The RR movable ring 214 can advance and retreat in the optical axis direction while being guided and restricted by the guide bars 204a and 204b. The front lens barrel 202, the intermediate frame 215, and the rear lens barrel 216 form a lens barrel main body that accommodates a lens or the like in a substantially sealed manner.

  The RR moving ring 214 that holds the focusing lens 201d is formed with a sleeve portion that is slidably fitted to the guide bars 204a and 204b, and the rack 213 is integrated with the RR moving ring 214 in the optical axis direction. It is assembled as follows.

  The stepping motor 212 rotationally drives a lead screw 212a formed integrally with its output shaft. A rack 213 assembled to the RR moving ring 214 is engaged with the lead screw 212a. When the lead screw 212a rotates, the RR moving ring 214 moves in the optical axis direction while being guided by the guide bars 204a and 204b. To do.

  Further, when the lens is moved using the stepping motor as described above, it is applied to the stepping motor after detecting that the holding frame is located at a predetermined reference position in the optical axis direction using a photo interrupter or the like. The absolute position of the holding frame is detected by continuously counting the number of drive pulses. However, the reference position may be detected using another detector such as a Hall element or an MR sensor.

  FIG. 11 shows an electrical configuration of the video camera. In this figure, the same reference numerals as those in FIGS. 10A and 10B denote the components of the lens barrel described in FIGS.

  Reference numeral 221 denotes a solid-state imaging device such as a CCD sensor or a CMOS sensor, and 222 denotes a drive mechanism for the variator lens 201b, which includes a DC motor 206 (or stepping motor), a gear train 207, a guide screw shaft 208, and the like.

  A driving mechanism 223 for the focusing lens 201d includes a stepping motor 212, a lead screw shaft 212a, a rack 213, and the like.

  Reference numeral 224 denotes a drive mechanism for an aperture device 235 disposed between the variator lens 201b and the afocal lens 201c.

  225 is a zoom encoder and 227 is a focus encoder. Each of these encoders detects the absolute position of the variator lens 201b and the focusing lens 201d in the optical axis direction. 9A and 9B, when a DC motor is used as the variator driving source, an absolute position encoder such as a volume or a magnetic type is used.

  Reference numeral 251 denotes an ND encoder, which employs a system in which a Hall element is disposed inside the ND drive source 250 to detect the rotational positional relationship between the rotor and the stator.

  A CPU 232 controls the video camera. Reference numeral 228 denotes a camera signal processing circuit which performs predetermined amplification, gamma correction, and the like on the output of the solid-state image sensor 221. The contrast signal of the video signal subjected to these predetermined processes passes through the AE gate 229 and the AF gate 230. That is, an optimum signal extraction range for exposure determination and focusing is set in this gate in the entire screen. The size of the gate may be variable or a plurality of gates may be provided.

  Reference numeral 231 denotes an AF signal processing circuit that processes an AF signal for AF (autofocus), and generates one or a plurality of outputs related to high-frequency components of the video signal. Reference numeral 233 denotes a zoom switch, and reference numeral 234 denotes a zoom tracking memory. The zoom tracking memory 234 stores focusing lens position information to be set according to the subject distance and the position of the variator lens 201b at the time of zooming. Note that the memory in the CPU 232 may be used as the zoom tracking memory.

  For example, when the photographer operates the zoom switch 233, the CPU 232 zooms in so that the predetermined positional relationship between the variator lens 201b and the focusing lens 201d calculated based on information in the zoom tracking memory 234 is maintained. The absolute position of the current variator lens in the optical axis direction as the detection result of 225, the calculated position of the variator lens 201b, and the absolute position of the current focus lens in the optical axis direction as the detection result of the focus encoder 227 The zoom drive mechanism 222 and the focussing drive mechanism 223 are driven and controlled so that the calculated positions where the focusing lens should be set coincide with each other.

  In the AF operation, the CPU 232 controls the driving of the focusing drive mechanism 223 so that the output of the AF signal processing circuit 231 shows a peak.

  Further, in order to obtain proper exposure, the CPU 232 controls the drive of the ND drive source 250 so that the average value of the output of the Y signal that has passed through the AE gate 229 is a predetermined value, and the output of the ND encoder 251 becomes this predetermined value. And control the amount of light.

  FIG. 1 is a diagram showing a cross section orthogonal to the optical axis of a gradation ND filter that is a feature of the present embodiment. Note that the vertical direction in FIG. 1 corresponds to the optical axis direction.

  In FIG. 1, reference numeral 1 denotes a transparent filter base formed of PET or the like. The filter base 1 serves as a base for constituting a gradation density region (hereinafter referred to as gradation region) and a uniform density region. In FIG. 1, the upper surface of the filter base 1 is referred to as a first surface 2, and the lower surface is referred to as a second surface 3.

Reference numeral 4A denotes an optical film (hereinafter referred to as a first optical film) composed of a multilayer film deposited on the first surface 2 of the filter base 1. Although the first optical film 4A in the figure has a six-layer structure, the number of layers is not limited to this. In this embodiment, the Al ₂ O ₃ layer and the TiO layer are alternately formed, but the material of each layer is not limited to this.

4B is an optical film (hereinafter referred to as a second optical film) made of a multilayer film deposited on the second surface 3 of the filter base 1. The second optical film 4B in the figure has a six-layer structure, but the number of layers is not limited to this. In this embodiment, the Al ₂ O ₃ layer and the TiO layer are alternately formed, but the material of each layer is not limited to this. Furthermore, the number of layers of the first optical film 4A and the second optical film 4B may be different, or the materials may be different.

  In this embodiment, the case where the optical film is formed by vapor deposition will be described. However, the optical film may be formed using a method other than vapor deposition, for example, a printing method.

  In FIG. 1, reference numeral 5 denotes a region having the minimum transmittance in the first optical film 4A (hereinafter referred to as a first minimum transmittance region). The transmittance (density) in this region is uniform. Reference numeral 6 denotes a gradation region (hereinafter referred to as a first gradation region) in the first optical film 4A, and the film thickness and transmittance (concentration) gradually increase toward the side opposite to the first minimum transmittance region 5 side. Decrease.

  Reference numeral 7 denotes a transparent region (hereinafter referred to as a first transparent region) where the first optical film 4A is not formed on the first surface 2 of the filter base 1.

  Reference numeral 8 denotes a region having the minimum transmittance in the second optical film 4B (hereinafter referred to as a second minimum transmittance region). The transmittance (density) in this region is uniform. Reference numeral 9 denotes a gradation region (hereinafter referred to as a second gradation region) in the second optical film 4B, which is directed toward the side opposite to the second minimum transmittance region 8 side, that is, the film of the first gradation region 6. The film thickness and transmittance (concentration) gradually decrease in the same direction as the thickness decreasing direction. That is, the increasing / decreasing directions of the transmittances of both gradation areas 6 and 9 are the same.

  Reference numeral 10 denotes a transparent region (hereinafter referred to as a second transparent region) in which the second optical film 4B is not formed on the second surface 3 of the filter base 1.

  In this embodiment, first, the first optical film 4A is vapor-deposited on the first surface 2 side of the filter base 1, and then the second optical film 4B is vapor-deposited on the second surface 3 side of the filter base 1. By doing so, an ND filter is manufactured. However, the manufacturing method by vapor deposition is not limited to this.

  In the present embodiment, the first minimum transmittance in the first gradation region 6 in the in-plane direction of the filter base 1 that is orthogonal to the optical axis (the horizontal direction in the figure, hereinafter referred to as the in-plane direction). The position of the end on the side of the region 5 (that is, the end of the first gradation region 6 on the small transmittance side and the boundary position between the first gradation region 6 and the first minimum transmittance region 5); , The end of the second gradation area 9 on the second transparent area 10 side (that is, the end of the second gradation area 9 on the large transmittance side, and the second gradation area 9 and the second transparent area) The position of the boundary position with respect to 10 substantially matches. In other words, the first gradation area 6 and the second gradation area 9 do not substantially overlap each other in the optical axis direction, and the entire second gradation area 9 overlaps the first minimum transmittance area 5. Is formed.

  Here, “substantially” means to include an error amount caused by a set position shift of the filter base 1 between the deposition of the first optical film 4A and the deposition of the second optical film 4B. Yes, specifically, in a range that allows an error amount of about ± 0.5 mm.

  In the present embodiment, the length of the first gradation area 6 and the length of the second gradation area 9 in the in-base direction are substantially equal.

  Furthermore, in the drawing, the edge region of the vapor deposition film is indicated by a broken line at the end of the first gradation region 6 on the large transmittance side (the first transparent region 7 side). This edge region is cut after vapor deposition in consideration of film peeling and the like. However, such an edge portion may be left and used as an ND filter.

  Note that the names of the respective parts, the meaning of “substantially”, and the processing of the edge region are the same in other embodiments described later.

  The lower side of FIG. 1 shows a transmittance characteristic graph of the ND filter of the present embodiment in which the horizontal axis is the position in the in-plane direction of the filter base 1 and the vertical axis is the transmittance. In this graph, it is shown that there is no “density step” at the boundary between the gradation region and the transparent region due to the cutting of the edge portion of the gradation region. Even if there is a level difference of about 5 or less, it is included in the present invention. Further, in this characteristic graph, the transmittance of the region 7 that is a transparent region on both the first surface 2 and the second surface 3, that is, the transmittance of the filter base itself is not actually 100%. Then, for simplicity, it is set to 100%. The same applies to other embodiments described later.

  In the graph, the characteristic indicated by the dotted line 11 shows that the optical film (minimum transmittance region 5 and gradation region 6) and the transparent region 7 are formed on the first surface 2, and the optical film is formed on the second surface 3. The transmittance characteristics when not performed are shown. The characteristic of the dotted line 11 corresponds to the characteristic of the conventional gradation ND filter. In the conventional gradation ND filter, the transmittance is set to about 1 to 4 steps of the EV value depending on the density design value of the minimum transmittance region. However, if the number of steps is set higher, the film thickness becomes too thick. This is not practical because it is difficult to manufacture. And the transmittance | permeability of the minimum transmittance | permeability area | region 5 at the time of providing the area | regions 5, 6, and 7 only in the 1st surface 2 side is 12.5% equivalent to 3 steps | paragraphs by EV value.

  With respect to such a conventional gradation ND filter, a second minimum transmittance region 8 having the same 25% transmittance as the first minimum transmittance region 5 on the second surface 3 side, and a second When the gradation area 9 and the second transparent area 10 are provided, the characteristic indicated by the graph 2 of the solid line 12 is obtained. That is, the final minimum transmittance (maximum density) is about 1.6% by the optical films 4A and 4B formed on both surfaces of the filter base 1, and the first and second gradation regions 6 and 9 are formed. Thus, it is possible to form a gradation portion that is longer than the conventional gradation ND filter (in other words, the transmittance change rate is small). In the present embodiment, the change rate of the transmittance in the gradation portion is almost constant.

  In the present embodiment, the case where the transmittance of the minimum transmittance region in the optical film on one side is the EV value of three stages has been described, but it may be four stages or any other number of stages. I do not care. In the case of four stages, the transmittance of 12.5% in FIG. 1 is 6.25%, and the transmittance of 1.6% is 0.4%. Can be obtained.

  In this way, for example, the light intensity can be adjusted by the gratation ND filter which can set the transmittance of 6 stages (3 stages on one side) or 8 stages (4 stages on one side) in terms of EV value, or between the ND filter and the image sensor. By performing exposure control by a combination with charge accumulation time control (electronic shutter) or the like, a conventional diaphragm device using diaphragm blades can be dispensed with. In addition, since the conventional diaphragm device causes image deterioration due to small diaphragm diffraction, it is desirable to perform exposure adjustment mainly using the ND filter as in this embodiment from this aspect.

  However, a diaphragm device as shown in FIG. 9 may be mounted. This diaphragm device is of a two-blade type, and has a configuration in which two diaphragm blades 405 and 406 are driven by a single rotary electromagnetic actuator (motor) 224 via a seesaw-type drive lever 402. In this diaphragm device, an electromagnetically driven actuator having a permanent magnet rotor (or a rotor magnetized on the outer peripheral surface of a metal body configured in a cylindrical shape) is used as a driving source for the diaphragm blades. Thus, the rotation position and the rotation amount (rotation angle) of the actuator are controlled by detecting the movement change of the magnetic poles on the outer peripheral surface of the rotor by the Hall element.

  If the aperture is too small when the subject is bright, image degradation due to light diffraction and reflection of dust attached to the lens due to an increase in the depth of focus becomes a problem. An example gradation ND filter is pasted so that the ND filter protrudes into the aperture, thereby preventing an extremely small aperture.

  In FIG. 9, an ND filter 414 is attached to the diaphragm blade 406. The seesaw drive lever 402 is connected to the groove portions 407 and 408 provided in the two blades by the interlocking portions 403 and 404, and the size of the aperture 413 is reduced by the rotation in the direction of the arrow 416 (or the reverse rotation thereof). It becomes variable.

  Here, as described above, when the light amount (exposure) control is performed only by the diaphragm blades, the F value at which the image deteriorates due to the diffraction phenomenon becomes brighter with the recent reduction in the pixel pitch of the image sensor, etc. In some cases, only F5.6 and F8 can be used.

  For this reason, the ND filter is attached to the diaphragm blade shown in FIG. 9 or, as proposed in Japanese Patent Laid-Open No. 2000-214514, the ND filter is connected to the optical path by a drive source different from the diaphragm drive source. By using the gradation filter of the present embodiment for what is inserted into and removed from the lens, the controllable light amount range and the number of steps can be increased without incurring small aperture diffraction.

  In the present embodiment, the case where the transmittance of the first minimum transmittance region 5 and the transmittance of the second minimum transmittance region 8 are the same has been described. The transmittance and the transmittance of the second minimum transmittance region 8 may be different. For example, the first minimum transmittance region 5 has a transmittance corresponding to four steps of the EV value, and the second minimum transmittance region 8 has a transmittance corresponding to three steps. Filters can also be configured. The same applies to the other embodiments in that the transmittance of the first minimum transmittance region 5 and the transmittance of the second minimum transmittance region 8 may be made different.

  FIG. 2 shows a gradation ND filter that is Embodiment 2 of the present invention. In the present embodiment, as in the first embodiment, the end position of the first gradation area 6 formed on the first surface 2 on the small transmittance side and the second position formed on the second surface 3 side. The boundary position on the large transmittance side of the gradation area 9 substantially matches. However, the length of the first gradation area 6 in the base plane direction is set to be shorter than the length of the second gradation area 9.

  Thereby, as indicated by the solid line 13 in the characteristic graph of FIG. 2, the change rate of the transmittance by the second gradation region 9 is made smaller than the change rate of the transmittance by the first gradation region 6.

  This is because, for example, when the amount of movement of the ND filter with respect to the rotation angle of the output shaft of the drive source increases as the transmittance decreases, due to the configuration of the drive mechanism that drives the ND filter, the output shaft This is effective when it is desired to obtain a certain amount of change in transmittance with respect to the amount of change in rotation angle.

  FIG. 3 shows a gradation ND filter that is Embodiment 3 of the present invention. In the present embodiment, as in the first embodiment, the end position of the first gradation area 6 formed on the first surface 2 on the small transmittance side and the second position formed on the second surface 3 side. The boundary position on the large transmittance side of the gradation area 9 substantially matches. However, the length of the first gradation area 6 in the base in-plane direction is set longer than the length of the second gradation area 9.

  As a result, as indicated by a solid line 14 in the characteristic graph of FIG. 13, the change rate of the transmittance due to the second gradation region 9 is made larger than the change rate of the transmittance due to the first gradation region 6.

  This is because when not only this ND filter but also a diaphragm device is used for exposure control, the area where the density of the ND filter is relatively low (the transmittance is relatively high) covers the diaphragm aperture. In view of the fact that the diaphragm device is often narrowed to some extent, this is effective when it is preferable to make the difference in density change of the gradation ND filters existing in the same diaphragm aperture constant.

  That is, in a situation where it is not necessary to reduce the amount of light, the diaphragm is not narrowed down. For example, the aperture diameter of the diaphragm is as large as 8 mm. The low rate part is 8 mm away. On the other hand, in a situation where it is necessary to reduce the amount of light, the diaphragm is narrowed down. For example, the aperture diameter is as small as 2 mm, so that the portion with high transmittance and the portion with low transmittance in the ND filter covering the opening. Is at a location 2 mm away.

  In both cases, if the difference in transmittance between the portion with the highest transmittance and the portion with the lowest transmittance is constantly made constant, the aperture is not narrowed (normally, the region where the transmittance of the ND filter is high). ) And the difference in transmittance at a location 2 mm away in the situation where the aperture is narrowed (usually in the region where the transmittance of the ND filter is low). Is desirable.

  Accordingly, it is preferable that the gradient (inclination) of the transmittance becomes tighter as the transmittance of the ND filter becomes lower, and this embodiment is suitable for such a case.

  FIG. 4 shows a gradient ND filter that is Embodiment 4 of the present invention. In the first to third embodiments, the case has been described in which the end position on the large transmittance side in the second gradation area 9 substantially matches the end position on the small transmittance side in the first gradation area 6. However, in the present embodiment, the end positions on the small transmittance side in the first and second gradation regions 6 and 9 substantially coincide with each other, and the transmission in the first and second gradation regions 6 and 9 occurs. The end positions on the larger side also substantially coincide with each other. Further, the increasing / decreasing directions of the transmittances of the gradation areas 6 and 9 are the same.

  As a result, the first and second gradation areas 6 and 9 substantially overlap in the optical axis direction, and a double-sided gradation effect in this range provides a large transmittance change rate that is difficult to achieve with only one-side gradation area. Can be produced.

  FIG. 5 shows a gradient ND filter that is Embodiment 5 of the present invention. In the present embodiment, the end positions on the large transmittance side in the first and second gradation areas 6 and 9 substantially coincide with each other, but the length of the first gradation area 6 in the base surface direction is set. The length of the second gradation area 9 is set to be shorter. That is, the end portion of the second gradation region 9 on the small transmittance side is provided at a position overlapping the first minimum transmittance region 5. Further, the increasing / decreasing directions of the transmittances of the gradation areas 6 and 9 are the same.

  Thereby, the change rate of the transmittance in the range in which the first and second gradation regions 6 and 9 overlap each other is the range in which the first minimum transmittance region 5 and the second gradation region 9 overlap. It can be made larger than the change rate of the transmittance.

  Thereby, the transmittance | permeability change advantageous in the case as demonstrated in Example 2 is realizable.

  FIG. 6 shows a gradient ND filter that is Embodiment 6 of the present invention. In this embodiment, in the base plane direction, in order from the minimum transmittance side, the end portion on the small transmittance side of the second gradation region 9, the end portion on the small transmittance side of the first gradation region 6, and the second An end portion on the large transmittance side of the gradation region 9 and an end portion on the large transmittance side of the first gradation region 6 are arranged.

  Thereby, the uniform transmittance range in which the first and second minimum transmittance regions 5 and 8 overlap in the optical axis direction and the gradation range in which the first minimum transmittance region 5 and the second gradation region 9 overlap. A gradation range in which the first and second gradation regions 6 and 9 overlap, a gradation range in which the first gradation region 9 and the second transparent region 10 overlap, and the first and second transparent regions 7 and A transparent range in which 10 overlap is formed.

  With this configuration, as indicated by a solid line 17 in the characteristic graph of FIG. 6, the change rate of the transmittance in the gradation range where the first and second gradation regions 6 and 9 overlap is represented by the gradation range on both sides of the gradation range. It becomes possible to make it larger than the rate of change.

  FIG. 7 shows a graduation ND filter that is Embodiment 7 of the present invention. In the present embodiment, the first gradation area 6 and the second gradation area 9 do not overlap at all, and the entire second gradation area 9 overlaps the first minimum transmittance area 5. Accordingly, as indicated by a solid line 18 in the characteristic graph of FIG. 7, the gradation range by the second gradation region 9, the region D where the transmittance higher than the minimum transmittance is constant, the first gradation, in order from the minimum transmittance side. It has a gradation range and a transparent range by the region 6.

  Here, in Japanese Patent Laid-Open No. 11-190867, in a diaphragm device (see FIG. 9) of a type in which a plurality of diaphragm blades are moved relative to each other, a driving range different from the driving range of the diaphragm driving source is used during still image shooting. There is a configuration in which an opening diameter different from the open aperture diameter can be obtained by setting a predetermined lever rotation angle. In addition to such an aperture device, there is also a type of aperture device that selects an aperture diameter of about 1 or 2 F-numbers in addition to the open diameter during still image shooting.

  The use of the gradation ND filter for these diaphragm devices is an image formation caused by a difference in transmittance within the diaphragm aperture, which occurs when a single density ND filter or a multi-density ND filter covers the middle of the diaphragm aperture. This is advantageous for performance degradation. However, there is still a case where it is difficult to sufficiently suppress the deterioration of the imaging performance because there is a difference in transmittance in the gradation state in the aperture opening. In particular, the influence cannot be ignored in a digital still camera with an increased number of pixels.

  For this reason, the gradation ND filter of this embodiment is provided in a diaphragm device of a type that selects two or three opening diameters including the open diameter, and the dimension of the constant transmittance region D provided in the middle of the gradation range. Is set to a size that can cover the open diameter or the other of these two or three aperture diameters, so that the entire aperture opening used for still image shooting is covered with a single density filter portion. Is possible.

  FIG. 12 shows an electrical configuration of a video camera provided with such an aperture device. In FIG. 12, 225 is a diaphragm device, 224 is a diaphragm drive source that drives diaphragm blades provided in the diaphragm device, and a stepping motor or the like is used.

  Based on the subject luminance information from the AE gate 229, the CPU 232 determines an aperture diameter to be set in an aperture device 235 of a type that can select an aperture diameter so that an optimum exposure can be obtained. While controlling the drive, it is determined whether or not the aperture opening is covered by the ND filter 252.

  As a result, when it is determined that the aperture opening selected by the ND filter is covered with the ND filter 252, the CPU 232 determines that the count value of the pulse signal from the ND encoder 251 becomes a predetermined value. Stepping motor) 250 is driven, and the position of ND filter 252 is controlled so as to cover the aperture opening in constant transmittance region D shown in FIG.

  FIG. 8 shows a graduation ND filter that is Embodiment 8 of the present invention. In the first to seventh embodiments, the case where the first optical film 4A and the second optical film 4B are formed on both surfaces of the filter base has been described. In this embodiment, the first optical film is formed on one surface of the filter base. A film 4A is formed, and a second optical film 4B is formed on the first optical film 4A.

  Here, in the present embodiment, as in the sixth embodiment, in order from the minimum transmittance side, the end portion of the second gradation region 9 on the small transmittance side in the second optical film 4B, the first optical film 4A. An end portion on the small transmittance side of the first gradation region 6, an end portion on the large transmittance side of the second gradation region 9, and an end portion on the large transmittance side of the first gradation region 6 are arranged. .

  Accordingly, the characteristic similar to that of the sixth embodiment indicated by the solid line 19 in the characteristic graph of FIG. 8, that is, the change rate of the transmittance in the gradation range where the first and second gradation areas 6 and 9 overlap, It is possible to obtain characteristics that are larger than the change rate of the gradation range on both sides.

  Note that the second optical film 4B in Examples 1 to 5 and 7 may be formed on the first optical film 4B to obtain the same characteristics as those of the examples.

  As described above, according to each of the above embodiments, by using a single filter base, the first and second optical films each having a gradation region are formed by a method such as vapor deposition or printing. The range of exposure control that can be achieved using only the ND filter can be expanded as compared with the conventional case. As a result, it is possible to perform exposure control of about 8 steps with an EV value using only the gradation ND filter, and it is possible to realize an optical apparatus that does not have a conventional diaphragm device.

  In addition, it can be realized with only a single optical film (multilayer film) by appropriately setting the position (end on the small transmittance side, end on the large transmittance side) and length of the gradation area of each optical film. It is difficult to enlarge the gradation range of the ND filter as a whole, reduce the minimum transmittance region, and select a change mode of transmittance.

  Furthermore, by providing a region with a constant transmittance in the middle of the gradation range and covering the aperture opening in this range, it is possible to shoot a still image with little image quality degradation.

1 is a cross-sectional view of a gradation ND filter that is Embodiment 1 of the present invention. Sectional drawing of the gradation ND filter which is Example 2 of this invention. Sectional drawing of the gradation ND filter which is Example 3 of this invention. Sectional drawing of the gradation ND filter which is Example 4 of this invention. Sectional drawing of the gradation ND filter which is Example 5 of this invention. Sectional drawing of the gradation ND filter which is Example 6 of this invention. Sectional drawing of the gradation ND filter which is Example 7 of this invention. Sectional drawing of the gradation ND filter which is Example 8 of this invention. The disassembled perspective view of the aperture_diaphragm | restriction apparatus suitable for implementation of this invention. Sectional drawing of the lens-barrel part of the video camera suitable for implementation of this invention. Sectional drawing of the lens-barrel part of the video camera suitable for implementation of this invention. FIG. 2 is a block diagram showing an electrical configuration of the video camera. FIG. 10 is a block diagram illustrating an electrical configuration of a video camera using a gradation ND filter according to a seventh embodiment.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Filter base 2 1st surface 3 2nd surface 4A 1st optical film 4B 2nd optical film 5 1st minimum transmittance | permeability area | region 6 1st gradation area | region 7 1st transparent area | region 8 2nd minimum Transmittance area 9 Second gradation area 10 Second transparent area

Claims (12)

An optical filter having a dimming action,
A filter base,
A first optical film formed on the filter base and having a first gradation region;
An optical filter comprising: a second optical film that is formed so that at least a portion thereof overlaps with the first optical film in the optical axis direction and has a second gradation region. The first optical film is formed on the first surface of the filter base;
The optical filter according to claim 1, wherein the second optical film is formed on a second surface of the filter base opposite to the first surface.   3. The optical filter according to claim 1, wherein an increasing / decreasing direction of the transmittance in the first gratation region and an increasing / decreasing direction of the transmittance in the second gratation region are the same.   4. The optical filter according to claim 1, wherein each of the first and second optical films includes a multilayer film.   5. The apparatus according to claim 1, wherein in the in-plane direction of the filter base, positions of at least one of both end portions of the first gradation region and the second gradation region are different from each other. The optical filter described in 1.   5. The optical filter according to claim 1, wherein in the in-plane direction of the filter base, the lengths of the first gradation area and the second gradation area are different from each other.   5. The optical filter according to claim 1, wherein the first gradation area and the second gradation area are formed so as not to overlap each other in the optical axis direction. 6. .   8. The change rate of the transmittance of the optical filter changes in a range where at least one of the first and second gradation regions is formed. 8. Optical filter. A light shielding member that forms an opening through which light passes and makes the size of the opening variable;
It has an optical filter as described in any one of Claim 1 to 8, The light quantity adjustment apparatus characterized by the above-mentioned. The optical filter according to any one of claims 1 to 8,
A light amount adjusting device, wherein the light amount is changed by moving the optical filter in a plane orthogonal to the optical axis. The light amount adjusting device according to claim 9 or 10,
And an optical system that forms an image on the light beam that has passed through the light amount adjusting device.   The lowest light transmittance in the range in which the first and second optical films are formed is a light transmittance of six steps or more with respect to the EV value of the optical device. The optical instrument described.

Images