JP2789860B2 - Optical low-pass filter and photographing system having the same - Google Patents
Optical low-pass filter and photographing system having the sameInfo
- Publication number
- JP2789860B2 JP2789860B2 JP3177199A JP17719991A JP2789860B2 JP 2789860 B2 JP2789860 B2 JP 2789860B2 JP 3177199 A JP3177199 A JP 3177199A JP 17719991 A JP17719991 A JP 17719991A JP 2789860 B2 JP2789860 B2 JP 2789860B2
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- Japan
- Prior art keywords
- pass filter
- optical low
- phase grating
- imaging system
- regions
- Prior art date
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Description
【０００１】[0001]
【産業上の利用分野】本発明は光学的ローパスフィルタ
ー及びそれを有した撮影系に関し、特にビデオカメラ、
電子スチルカメラ等で撮像管や撮像板（ＣＣＤ）等を用
いて画像を離散的に得る際に好適な光学的ローパスフィ
ルター及びそれを有した撮影系に関するものである。BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical low-pass filter and a photographing system having the same, and more particularly to a video camera,
The present invention relates to an optical low-pass filter suitable for discretely obtaining images using an image pickup tube or an image pickup plate (CCD) with an electronic still camera or the like, and an imaging system having the same.
【０００２】[0002]
【従来の技術】一般に離散的画素構造を有する固体撮像
素子を用いたビデオカメラ等では画像情報を光学的に空
間サンプリングして出力画像を得ている。この場合被写
体にサンプリング周波数以上の高空間周波数成分が含ま
れていると被写体が有していな構造や色あい等の偽信号
が発生してくる。即ち撮影系によって採取することので
きない周波数成分（ナイキスト周波数を越える周波数成
分）は画像情報として再現することができず、所謂波形
歪み（エイリアシス）、モアレ縞、偽色等が形成される
原因となってくる。この為従来より光学的ローパスフィ
ルターを撮影系の一部に配置して被写体の高空間周波数
成分を制限している。2. Description of the Related Art Generally, in a video camera or the like using a solid-state imaging device having a discrete pixel structure, an image is optically spatially sampled to obtain an output image. In this case, if the subject contains a high spatial frequency component equal to or higher than the sampling frequency, a false signal such as a structure or a color tone that the subject does not have is generated. That is, frequency components that cannot be collected by the imaging system (frequency components exceeding the Nyquist frequency) cannot be reproduced as image information, and cause so-called waveform distortion (alias), moire fringes, false colors, and the like. Come. For this reason, conventionally, an optical low-pass filter is arranged in a part of a photographing system to limit a high spatial frequency component of a subject.
【０００３】光学的ローパスフィルター及びそれを有し
た撮影系は従来より種々の型のものが提案されている。
このうち例えば特公昭５２−２２２４７号公報では位相
格子を用いた光学的ローパスフィルターを提案してい
る。同公報では断面形状が台形波状の位相格子を１次元
方向に連続的に配置し、そのときの頂上平坦部と傾斜面
の形状やピッチ等を特定し、良好なるローパス効果を得
ている。Various types of optical low-pass filters and photographing systems having the same have conventionally been proposed.
Among them, for example, Japanese Patent Publication No. 52-22247 proposes an optical low-pass filter using a phase grating. In this publication, a phase grating having a trapezoidal wave-shaped cross section is continuously arranged in a one-dimensional direction, and the shape, pitch, and the like of the flat portion and the inclined surface at that time are specified, and a good low-pass effect is obtained.
【０００４】又、特公昭５６−２９３６号公報では位相
格子よる成る光学的ローパスフィルターを撮影系の一部
に設けて使用する場合、絞りの開口径を小さくしたとき
でも所定のローパス効果が得られるようにした撮影系を
提案している。即ち同公報では最小絞りのときであって
も、少なくとも位相格子の２周期分が絞り開口内に含ま
れるように絞りの開口形状を位相格子の周期方向を長手
方向とする細長い開口形状としている。これにより絞り
を小絞りにしたときでも一定のローパス効果が得られる
ようにしている。In Japanese Patent Publication No. 56-2936, when an optical low-pass filter composed of a phase grating is provided in a part of a photographing system and used, a predetermined low-pass effect can be obtained even when the aperture diameter of the diaphragm is reduced. We have proposed such a shooting system. That is, in the publication, even at the time of the minimum aperture, the aperture shape of the aperture is set to be an elongated aperture shape whose longitudinal direction is the periodic direction of the phase grating so that at least two periods of the phase grating are included in the aperture. Thus, a constant low-pass effect can be obtained even when the aperture is set to a small aperture.
【０００５】[0005]
【発明が解決しようとする課題】一般に位相格子より成
る光学的ローパスフィルターを用いて一定のローパス効
果を得るには位相格子の複数の周期分、例えば２周期分
に相当する領域に光束を通過させ回折させる必要があ
る。この為、撮影系の絞りをあまり小さく絞ることがで
きず、例えば被写体輝度が高く絞り開口を小絞りにしな
ければならないときはＮＤフィルターを併用して通過光
量を減らし、絞り径が一定以下とならないようにしてい
る。Generally, in order to obtain a constant low-pass effect using an optical low-pass filter comprising a phase grating, a light beam is passed through a region corresponding to a plurality of periods, for example, two periods of the phase grating. It needs to be diffracted. For this reason, the aperture of the photographing system cannot be reduced too small. For example, when the brightness of the subject is high and the aperture aperture needs to be small, the amount of light passing therethrough is reduced by using an ND filter, and the aperture diameter does not fall below a certain value. Like that.
【０００６】しかしながらＮＤフィルターを用いて通過
光量を低下させる方法は得られる画像のボケ味が悪くな
り、又ＮＤフィルターを撮影系の一部に装着しておかね
ばならず、装置全体が複雑化してくるという問題点があ
った。However, the method of reducing the amount of transmitted light by using the ND filter deteriorates the blurring of the obtained image, and requires the ND filter to be attached to a part of the photographing system, which complicates the entire apparatus. There was a problem of coming.
【０００７】これに対して先の特公昭５６−２９３６号
公報では光束が少なくとも位相格子の２周分を通過しな
いと一定のローパス効果が得られないとし、位相格子の
少なくとも２周期分に相当する領域に光束が入射するよ
うに絞りの開口形状を位相格子の周期方向に細長くなる
ように構成している。この為絞り装置の構成が複雑化し
てくるという問題点があった。On the other hand, Japanese Patent Publication No. 56-2936 discloses that a certain low-pass effect cannot be obtained unless the light beam passes through at least two rounds of the phase grating, which corresponds to at least two periods of the phase grating. The aperture shape of the stop is configured to be elongated in the period direction of the phase grating so that the light beam enters the region. For this reason, there has been a problem that the configuration of the diaphragm device becomes complicated.
【０００８】又、同公報では光束が位相格子の２周期以
下の領域を通過したときのローパス効果については何ん
ら考慮されていなかった。In this publication, no consideration is given to the low-pass effect when a light beam passes through a region of two phases or less of the phase grating.
【０００９】本発明は位相格子より成る光学的ローパス
フィルターを用いたとき、絞り開口を小さく絞り、位相
格子の２周期以下に相当する領域に光束が通過するよう
にしても、即ち絞り値を種々と変化させても常に一定の
ローパス効果が容易に得られ、良好なる光学性能を有し
た撮影が可能な光学的ローパスフィルター及びそれを有
した撮影系の提供を目的とする。According to the present invention, when an optical low-pass filter comprising a phase grating is used, the aperture opening is made smaller so that the light beam passes through a region corresponding to two periods or less of the phase grating, that is, the aperture value is variously changed. Therefore, it is an object of the present invention to provide an optical low-pass filter which can easily obtain a constant low-pass effect even when it is changed and can perform photographing with good optical performance, and a photographing system having the same.
【００１０】[0010]
【課題を解決するための手段】本発明の光学的ローパス
フィルターは、（１−１）断面形状が台形波状の位相格
子を一次元方向に配列した光学的ローパスフィルターに
おいて該光学的ローパスフィルターをその中心部から該
位相格子の配列方向を境に２つの領域に分割したとき、
該２つの領域の境界において、各々の領域の位相格子が
配列方向にずれていることを特徴としている。According to the present invention, there is provided an optical low-pass filter comprising: (1-1) an optical low-pass filter in which phase gratings having a trapezoidal cross section are arranged in a one-dimensional direction; When divided into two regions from the center to the direction of arrangement of the phase grating,
At the boundary between the two regions, the phase grating of each region is shifted in the arrangement direction.
【００１１】特に、(1-1-1)前記２つの領域の位相格子
のずれ量が、該位相格子のピッチの略１／２であるこ
と、(1-1-2)前記光学的ローパスフィルターの断面形状
は、凸部が台形波状であること、(1-1-3)前記光学的ロ
ーパスフィルターの断面形状は、凹部が台形波状である
こと等を特徴としている。In particular, (1-1-1) the shift amount of the phase grating between the two regions is approximately １ ／ of the pitch of the phase grating, and (1-1-2) the optical low-pass filter. Is characterized in that the convex portion has a trapezoidal wave shape, and (1-1-3) the optical low-pass filter has a sectional shape in which the concave portion has a trapezoidal wave shape.
【００１２】本発明の光学的ローパスフィルターを有し
た撮影系は、（２−１）前述の構成（１−１）の光学的
ローパスフィルターを有していることを特徴としてい
る。（２−２）断面形状が台形波状の位相格子を一次元
方向に配列した光学的ローパスフィルターを有した撮影
系であって、該光学的ローパスフィルターをその中心部
から該位相格子の配列方向を境に２つの領域に分割した
とき、該２つの領域の境界線において各々の領域の位相
格子は配列方向にずれており、前記撮影系の絞りの開口
中心に該２つの領域の境界又は前記位相格子の平坦部が
位置するよう該光学的ローパスフィルターを配置したこ
とを特徴としている。特に、(2-2-1)前記２つの領域の
位相格子のずれ量が、該位相格子のピッチの略１／２で
あること、(2-2-2)前記光学的ローパスフィルターの基
板に垂直に入射した光束のうち位相格子の傾斜面を通過
した光束の屈折角をθｒ 、該位相格子の１次回折角を
θｆ 、該位相格子の傾斜面と該基板とのなす角をθ、
該位相格子の材質の屈折率をｎ、使用波長をλ、該位相
格子の頂上平坦部の幅をＤとし、 θｒ ＝（ｎ−１）θ θｆ ＝ｓｉｎ−１（λ／Ｐ） としたとき ０．１５＜Ｄ／Ｐ＜０．３５ ０．５＜θｒ ／θｆ ＜１．４ なる条件を満足すること、(2-2-3)前記撮影系は固体撮
像素子を有しており、前記光学的ローパスフィルターを
その位相格子方向と該固定撮像素子の水平走査方向との
なす角をｋとしたとき ４５°＜ｋ＜７５° なる条件を満足するように配置したこと等を特徴として
いる。A photographing system having an optical low-pass filter according to the present invention is characterized in that (2-1) the optical low-pass filter has the above-mentioned configuration (1-1). (2-2) An imaging system having an optical low-pass filter in which trapezoidal wave-shaped phase gratings are arranged in a one-dimensional direction, wherein the optical low-pass filter is arranged such that the arrangement direction of the phase grating is changed from the center thereof. When divided into two regions at the boundary, the phase grating of each region is shifted in the arrangement direction at the boundary line between the two regions, and the boundary of the two regions or the phase at the center of the aperture of the aperture of the imaging system. The optical low-pass filter is arranged so that the flat portion of the grating is located. In particular, (2-2-1) the shift amount of the phase grating in the two regions is approximately １ ／ of the pitch of the phase grating, and (2-2-2) the substrate of the optical low-pass filter Of the vertically incident light flux, the refraction angle of the light flux passing through the inclined surface of the phase grating is θ r , the first-order diffraction angle of the phase grating is θ f , the angle between the inclined surface of the phase grating and the substrate is θ,
The refractive index of the material of the phase grating is n, the wavelength used is λ, the width of the flat top of the phase grating is D, and θ r = (n−1) θ θ f = sin −1 (λ / P) 0.15 <D / P <0.35 0.5 <θ r / θ f <1.4, and (2-2-3) the imaging system has a solid-state imaging device Wherein the optical low-pass filter is arranged so as to satisfy a condition of 45 ° <k <75 ° when an angle between the phase grating direction and the horizontal scanning direction of the fixed image pickup device is k. Features.
【００１３】[0013]
【実施例】図１（Ａ）（Ｂ）は本発明の光学的ローパス
フィルターの実施例１の正面図と断面図、図２は本発明
の光学的ローパスフィルターの断面概略図、図３は本発
明の光学的ローパスフィルターを有した撮影系の要部概
略図である。1A and 1B are a front view and a sectional view of an optical low-pass filter according to a first embodiment of the present invention, FIG. 2 is a schematic sectional view of the optical low-pass filter of the present invention, and FIG. FIG. 1 is a schematic view of a main part of a photographing system having an optical low-pass filter according to the present invention.
【００１４】図中、１は光学的ローパスフィルターであ
り、断面形状が台形波状の位相格子を連続的に配置した
構成より成っている。In FIG. 1, reference numeral 1 denotes an optical low-pass filter having a structure in which phase gratings having a trapezoidal cross section are continuously arranged.
【００１５】光学的ローパスフィルター１はその中心部
０から位相格子の配列方向（ｘ方向）を境にして２つの
領域に分割し、該分割した２つのローパスフィルター部
１０１，１０２を互いに位相格子の配列方向（ｘ方向）
に１ピッチＰ以内にずらして、即ち位相ずらしをして配
置している。同図では位相格子の１／２ピッチＰずらし
た場合を示している。The optical low-pass filter 1 is divided into two regions from the center 0 thereof in the direction of the arrangement of the phase grating (x direction), and the two divided low-pass filter portions 101 and 102 are mutually connected to the phase grating. Array direction (x direction)
Are shifted within one pitch P, that is, the phases are shifted. The figure shows a case where the phase grating is shifted by ピ ッ チ pitch P of the phase grating.
【００１６】２は撮影系、３は絞りである。光学的ロー
パスフィルター１は絞り３近傍に配置している。４はＣ
ＣＤ等から成る固体撮像素子である。Reference numeral 2 denotes a photographing system, and 3 denotes an aperture. The optical low-pass filter 1 is arranged near the stop 3. 4 is C
This is a solid-state imaging device made of a CD or the like.
【００１７】光学的ローパスフィルター１はその位相格
子方向が固体撮像素子４の水平走査方向４ａに対して角
度ｋだけ傾けて配置している。The optical low-pass filter 1 is arranged such that the phase grating direction thereof is inclined by an angle k with respect to the horizontal scanning direction 4a of the solid-state imaging device 4.
【００１８】光学的ローパスフィルターを構成する位相
格子は一体成形され製作されるが、その断面形状は図２
に示すように台形波状の台形部１ａを平行平板状の基板
１ｂ面上に連続的にピッチＰで１次元方向に配列したよ
うな形状より成っている。The phase grating constituting the optical low-pass filter is integrally molded and manufactured.
As shown in the figure, the trapezoidal wave-shaped trapezoidal portions 1a are arranged in a one-dimensional direction at a pitch P continuously on the surface of the parallel plate-like substrate 1b.
【００１９】同図では台形部１ａは幅Ｄの頂上平坦部１
ｃと基板１ｂへ射影したときの長さＥの傾斜面１ｆより
成っている。In the figure, the trapezoidal portion 1a is a flat top portion 1 having a width D.
c and an inclined surface 1f having a length E when projected onto the substrate 1b.
【００２０】Ｃ１は光学的ローパスフィルター１の中心
線であり、一方のローパスフィルター部の位相格子の境
界部１ｈと一致している。Ｃ２は撮影系２の絞り３の開
口中心を示している。C1 is the center line of the optical low-pass filter 1, which coincides with the boundary 1h of the phase grating of one of the low-pass filters. C2 indicates the center of the aperture of the stop 3 of the photographing system 2.
【００２１】本実施例では光学的ローパスフィルター１
を構成する２つのローパスフィルター部１０１，１０２
のうち一方のローパスフィルター部１０２の中心線Ｃ１
（境界部）が絞り３の開口中心Ｃ２に略一致するように
撮影系中に配置している。In this embodiment, the optical low-pass filter 1 is used.
Of two low-pass filter units 101 and 102
Center line C1 of one of the low-pass filter units 102
(Boundary part) is arranged in the photographing system such that it substantially coincides with the aperture center C2 of the stop 3.
【００２２】本実施例では以上のように光学的ローパス
フィルターの形状及び撮影系に配置するときの姿勢を特
定することにより被写体輝度が高く絞り３を小さく絞
り、例えば通過光束が位相格子の２周期以下となっても
台形波の頂上平坦部１ｃと傾斜面１ｆの面積比をバラン
ス良く保ち通過光束を効果的に回折させ、光学性能の低
下を防止しつつ所定のローパス効果が容易に得られるよ
うにしている。In the present embodiment, as described above, the shape of the optical low-pass filter and the posture when the optical low-pass filter is arranged in the photographing system are specified so that the subject brightness is high and the aperture 3 is small. Even in the following case, a predetermined low-pass effect can be easily obtained while keeping the area ratio between the flat top portion 1c and the inclined surface 1f of the trapezoidal wave in a well-balanced state and effectively diffusing the passing light beam while preventing a decrease in optical performance. I have to.
【００２３】この他本発明において光学的ローパスフィ
ルターを撮影系中に配置し光学性能の低下を防止しつつ
良好なるローパス効果を得るには次の諸条件を満足させ
るのが良い。In addition, in order to obtain a good low-pass effect while preventing a decrease in optical performance by arranging an optical low-pass filter in the photographing system in the present invention, it is preferable to satisfy the following conditions.
【００２４】（イ）前記光学的ローパスフィルターの基
板に垂直に入射した光束のうち位相格子の傾斜面を通過
した光束の屈折角をθr 、該位相格子の１次回折角をθ
f 、該位相格子の傾斜面と該基板とのなす角をθ、該位
相格子の材質の屈折率をｎ、使用波長をλ、該位相格子
の頂上平坦部の幅をＤとし、 θr ＝（ｎ−１）θ θf ＝ｓｉｎ-1（λ／Ｐ） としたとき ０．１５＜Ｄ／Ｐ＜０．３５ ‥‥‥‥‥‥（１） ０．５＜θr ／θf ＜１．４ ‥‥‥‥‥‥（２） なる条件を満足すること。(A) Of the light beams incident perpendicularly to the substrate of the optical low-pass filter, the refraction angle of the light beam that has passed through the inclined surface of the phase grating is θ r , and the first-order diffraction angle of the phase grating is θ
f , the angle between the inclined surface of the phase grating and the substrate is θ, the refractive index of the material of the phase grating is n, the wavelength used is λ, the width of the flat top of the phase grating is D, and θ r = (N-1) θ θ f = sin −1 (λ / P) 0.15 <D / P <0.35 (1) 0.5 <θ r / θ f < The condition of 1.4２ (2) must be satisfied.
【００２５】条件式（１）の下限値を越えると絞り開口
を位相格子の２周期以内に絞り込んだとき頂上平坦部の
面積の比率が少なくなり、０次光のスペクトルが弱まり
撮影系の解像力が低下してくるので良くない。If the lower limit of conditional expression (1) is exceeded, the ratio of the area of the flat portion at the top will decrease when the aperture is narrowed within two periods of the phase grating, the spectrum of the zero-order light will be weakened, and the resolution of the photographing system will be reduced. It is not good because it falls.
【００２６】又、上限値を越えると絞り開口を位相格子
の２周期以内に絞り込んだとき逆に頂上平坦部の面積の
比率が大きくなりすぎ、０次光のスペクトルが１次回折
光のスペクトルよりも強くなりすぎローパス効果が低下
してくるので良くない。On the other hand, if the upper limit value is exceeded, when the aperture is narrowed within two periods of the phase grating, the ratio of the area of the flat portion on the top becomes too large, and the spectrum of the zero-order light is larger than the spectrum of the first-order diffracted light. It is not good because it becomes too strong and the low-pass effect decreases.
【００２７】条件式（２）の下限値を越えると波動光学
の原理に支配される位相格子の２周期以上の絞り開口の
ときの１次回折光の射出角（位相格子の１次回折角を一
致）θf に対して幾何光学の原理に支配される位相格子
の２周期以下の絞り開口のときの１次回折光の射出角θ
r （位相格子の傾斜面の屈折角に一致）が小さくなるの
でローパス効果が低下してくる。特に頂上平坦部と傾斜
面との面積比が略等しく０次光と１次回折光の強度が等
しい場合であってもローパス効果が低下してくる。If the lower limit of conditional expression (2) is exceeded, the exit angle of the first-order diffracted light at the time of the aperture opening of two or more periods of the phase grating governed by the principle of the wave optics (the primary diffraction angle of the phase grating coincides). For θ f , the exit angle θ of the first-order diffracted light at the time of the aperture opening of two or less periods of the phase grating governed by the principle of geometrical optics
Since r (corresponding to the refraction angle of the inclined surface of the phase grating) becomes small, the low-pass effect is reduced. In particular, even when the area ratio between the flat top portion and the inclined surface is substantially equal and the intensity of the 0th-order light and the 1st-order diffracted light is equal, the low-pass effect is reduced.
【００２８】逆に条件式（２）の上限値を越えて１次回
折光の射出角θrが回折角θf より大きくなりすぎると
絞り開口を位相格子の２周期以下に絞り込んだとき撮影
系の解像力が低下してくるので良くない。Conversely, if the exit angle θ r of the first-order diffracted light exceeds the upper limit value of the conditional expression (2) and becomes larger than the diffraction angle θ f , the aperture of the imaging system is reduced when the aperture opening is narrowed to two periods or less of the phase grating. It is not good because the resolving power decreases.
【００２９】（ロ）前記撮影系は固体撮像素子を有して
おり、前記光学的ローパスフィルターをその位相格子方
向と該固定撮像素子の水平走査方向とのなす角をｋとし
たとき ４５°＜ｋ＜７５° ‥‥‥‥‥‥（３） なる条件を満足するように配置したこと。(B) The photographing system has a solid-state image sensor. When the angle between the phase grating direction of the optical low-pass filter and the horizontal scanning direction of the fixed image sensor is k, 45 ° < k <75 ° ‥‥‥‥‥‥ (3) The arrangement is such that the following condition is satisfied.
【００３０】条件式（３）の下限値を越えて角度ｋが小
さくなりすぎると撮影系の解像力が大きく低下してくる
ので良くない。又上限値を越えると解像力は向上するが
垂直走査方向のローパス効果がなくなってくるので良く
ない。If the angle k is too small below the lower limit of conditional expression (3), the resolving power of the photographing system is greatly reduced, which is not good. If the value exceeds the upper limit, the resolving power is improved, but the low-pass effect in the vertical scanning direction disappears, which is not good.
【００３１】図４は本発明の光学的ローパスフィルター
（Ｃ）と断面形状が台形波状の位相ずらしをしていない
光学的ローパスフィルター（Ａ），（Ｂ）を用いたとき
のスペクトル射出角とスペクトル強度比を示す説明図で
ある。FIG. 4 shows a spectrum emission angle and a spectrum when the optical low-pass filter (C) of the present invention and the optical low-pass filters (A) and (B) each having a trapezoidal cross section without phase shift are used. It is explanatory drawing which shows an intensity ratio.
【００３２】図４（Ａ）は絞り開口中心Ｃ２が台形波状
の頂上平坦部の中心に位置しているとき、図４（Ｂ）は
絞り開口中心Ｃ２が台形波状の境界部に位置していると
きを示している。光学的ローパスフィルター（Ａ），
（Ｂ）は後述する数値実施例１と同じ形状を有してお
り、ただ位相ずらしを行なっていないものである。FIG. 4A shows that the center C2 of the aperture opening is located at the center of the trapezoidal wave-shaped flat top, and FIG. 4B shows that the center C2 of the aperture opening is located at the boundary of the trapezoidal waveform. Shows the time. Optical low-pass filter (A),
(B) has the same shape as that of Numerical Example 1 to be described later, but does not perform phase shift.
【００３３】又、同図では光束が位相格子の２周期分か
ら０．２５周期へと種々と変化させて入射した場合を示
している。FIG. 3 shows a case where a light beam is incident with various changes from two periods of the phase grating to 0.25 period.
【００３４】光学的ローパスフィルター（Ａ）では絞り
開口が位相格子の１．５〜１．７５周期において０次光
の強度が１次回折光に比べて弱まり撮影系の解像力が低
下してくる。又、０．５周期以下では逆に０次光の強度
が強くなりすぎローパス効果が低下してくる。In the optical low-pass filter (A), the intensity of the 0th-order light becomes weaker than that of the 1st-order diffracted light at the aperture of 1.5 to 1.75 periods of the phase grating, and the resolution of the photographing system is reduced. On the other hand, when the period is 0.5 cycles or less, the intensity of the zero-order light is too strong, and the low-pass effect is reduced.
【００３５】光学的ローパスフィルター（Ｂ）では絞り
開口が位相格子の０．７５周期以下になると０次光が消
失し、撮影系の解像が低下してくる。In the optical low-pass filter (B), the 0th-order light disappears when the stop aperture becomes 0.75 periods or less of the phase grating, and the resolution of the photographing system decreases.
【００３６】このように光学的ローパスフィルター
（Ａ），（Ｂ）では絞り径が位相格子の約２周期以下と
なると撮影系の絞り値によってローパス効果、又は撮影
系の解像力が低下してくる場合があった。As described above, in the case of the optical low-pass filters (A) and (B), when the aperture diameter becomes about two cycles or less of the phase grating, the low-pass effect or the resolution of the imaging system is reduced by the aperture value of the imaging system. was there.
【００３７】これに対して本発明に係る光学的ローパス
フィルター（Ｃ）においては絞り開口が位相格子の２周
期以下となってもスペクトル強度の変化が少なく、０次
光と１次回折光の強度のバランスが良く２周期以上のと
きと略同様のローパス効果を得ることができる。On the other hand, in the optical low-pass filter (C) according to the present invention, even when the aperture is smaller than two periods of the phase grating, the change in the spectral intensity is small, and the intensity of the 0th-order light and the 1st-order diffracted light is small. A well-balanced low-pass effect similar to that obtained when two or more cycles are obtained can be obtained.
【００３８】尚、以上の実施例において２つのローパス
フィルター部１０１，１０２のｘ方向のずれが１／２ピ
ッチＰのときは絞り開口中心Ｃ２を台形波状の境界部１
ｈの代わりに頂上平坦部１ｃの略中心に位置するように
しても前述と同様の効果を得ることをができる。In the above embodiment, when the shift in the x direction between the two low-pass filter portions 101 and 102 is ピ ッ チ pitch P, the aperture opening center C2 is set to the trapezoidal boundary 1
The same effect as described above can be obtained even if it is positioned substantially at the center of the flat top portion 1c instead of h.
【００３９】又、以上の各実施例において位相格子の凹
凸形状は図５に示すように全く逆であっても同様の効果
を得ることができる。In each of the above embodiments, the same effect can be obtained even if the unevenness of the phase grating is completely reversed as shown in FIG.
【００４０】次に本発明の光学的ローパスフィルターの
形状に関する諸数値及び前述の各条件式との関係を示
す。Next, numerical values relating to the shape of the optical low-pass filter of the present invention and the relationship with the above-described conditional expressions will be described.
【００４１】 （数値実施例１） （数値実施例２） （数値実施例３） P =1.88 P =1.88 P =1.88 D =0.47 D =0.376 D =0.564 E =0.705 E =0.752 E =0.658 θ =0.0378° θ = 0.030° θ = 0.045° n =1.49 n =1.49 n =1.49 λ =0.00055 λ =0.00055 λ =0.00055 K =60° K =65° K =55° D/P =0.25 D/P =0.2 D/P =0.3 θr/θf=1.1 θr/θf=0.88 θr/θf=1.32 K = 60 ° K = 65 ° K = 55 °(Numerical Example 1) (Numerical Example 2) (Numerical Example 3) P = 1.88 P = 1.88 P = 1.88 D = 0.47 D = 0.376 D = 0.564 E = 0.705 E = 0.522 E = 0.658 θ = 0.0378 ° θ = 0.030 ° θ = 0.045 ° n = 1.49 n = 1.49 n = 1.49 λ = 0.00055 λ = 0.00055 λ = 0.00055 K = 60 ° K = 65 ° K = 55 ° D / P = 0.25 D / P = 0.2 D / P = 0.3 θ r / θ f = 1.1 θ r / θ f = 0.88 θ r / θ f = 1.32 K = 60 ° K = 65 ° K = 55 °
【００４２】[0042]
【発明の効果】本発明によれば前述の如く光学的ローパ
スフィルターの各要素を設定することにより、光学的ロ
ーパスフィルターを撮影系の一部に配置して撮影する際
に絞り開口を小絞りにして例えば位相格子の２周期以下
に相当する領域に光束が通過するようにしても、即ち絞
り値を種々と変化させても常に一定のローパス効果が容
易に得られ、又ＮＤフィルターの濃度を薄くしたり、使
用枚数を減らすことができボケ味の良い良好なる光学性
能を有した撮影が可能な光学的ローパスフィルター及び
それを有した撮影系を達成することができる。According to the present invention, by setting each element of the optical low-pass filter as described above, the aperture opening can be reduced when the optical low-pass filter is arranged in a part of the photographing system for photographing. For example, even if the light beam passes through a region corresponding to, for example, two periods or less of the phase grating, that is, even if the aperture value is variously changed, a constant low-pass effect can always be easily obtained, and the density of the ND filter can be reduced. An optical low-pass filter capable of reducing the number of sheets to be used, reducing the number of sheets used, and having good optical performance with good blur, and an imaging system having the same can be achieved.
【図１】 本発明の光学的ローパスフィルターの実施例
１の正面図と側面図FIG. 1 is a front view and a side view of Embodiment 1 of an optical low-pass filter of the present invention.
【図２】 図１の一部分の断面概略図FIG. 2 is a schematic cross-sectional view of a part of FIG.
【図３】 本発明の光学的ローパスフィルターを有した
撮影系の要部概略図FIG. 3 is a schematic diagram of a main part of a photographing system having an optical low-pass filter according to the present invention.
【図４】 本発明の光学的ローパスフィルターの実施例
と位相ずらしをしていない光学的ローパスフィルターの
スペクトル強度の比較図FIG. 4 is a comparison diagram of the spectral intensity of an optical low-pass filter according to an embodiment of the present invention and an optical low-pass filter without phase shift;
【図５】 本発明の実施例２の要部断面図FIG. 5 is a sectional view of a main part of a second embodiment of the present invention.
１ 光学的ローパスフィルター １ａ 台形部 １ｂ 基板 １ｃ 頂上平坦部 ２ 撮影系 ３ 絞り ４ 撮像素子 Ｃ１ 中心線 Ｃ２ 開口中心 DESCRIPTION OF SYMBOLS 1 Optical low-pass filter 1a Trapezoid part 1b Substrate 1c Flat top 2 Imaging system 3 Aperture 4 Image sensor C1 Center line C2 Opening center
Claims (9)
方向に配列した光学的ローパスフィルターにおいて該光
学的ローパスフィルターをその中心部から該位相格子の
配列方向を境に２つの領域に分割したとき、該２つの領
域の境界において、各々の領域の位相格子が配列方向に
ずれていることを特徴とする光学的ローパスフィルタ
ー。In an optical low-pass filter in which trapezoidal phase gratings having a trapezoidal cross section are arranged in a one-dimensional direction, the optical low-pass filter is divided into two regions from the center of the filter with the arrangement direction of the phase grating as a boundary. An optical low-pass filter characterized in that, at the boundary between the two regions, the phase grating of each region is shifted in the arrangement direction.
該位相格子のピッチの略１／２であることを特徴とする
請求項１の光学的ローパスフィルター。2. A shift amount of a phase grating between the two regions is as follows:
2. The optical low-pass filter according to claim 1, wherein the pitch of the phase grating is approximately 1/2.
状は、凸部が台形波状であることを特徴とする請求項１
又は２の光学的ローパスフィルター。3. A cross-sectional shape of the optical low-pass filter, wherein a convex portion has a trapezoidal wave shape.
Or 2 optical low pass filters.
状は、凹部が台形波状であることを特徴とする請求項１
又は２の光学的ローパスフィルター。4. A cross-sectional shape of the optical low-pass filter, wherein the concave portion has a trapezoidal wave shape.
Or 2 optical low pass filters.
的ローパスフィルターを有することを特徴とする撮影
系。5. An imaging system comprising the optical low-pass filter according to claim 1.
方向に配列した光学的ローパスフィルターを有した撮影
系であって、該光学的ローパスフィルターをその中心部
から該位相格子の配列方向を境に２つの領域に分割した
とき、該２つの領域の境界線において各々の領域の位相
格子は配列方向にずれており、前記撮影系の絞りの開口
中心に該２つの領域の境界又は前記位相格子の平坦部が
位置するよう該光学的ローパスフィルターを配置したこ
とを特徴とする光学的ローパスフィルターを有した撮影
系。6. An imaging system having an optical low-pass filter in which trapezoidal phase gratings having a cross-sectional shape arranged in a one-dimensional direction, wherein the optical low-pass filter is arranged so that the arrangement direction of the phase grating is changed from the center of the optical low-pass filter. When divided into two regions at the boundary, the phase grating of each region is shifted in the arrangement direction at the boundary line between the two regions, and the boundary of the two regions or the phase at the center of the aperture of the aperture of the imaging system. An imaging system having an optical low-pass filter, wherein the optical low-pass filter is arranged so that a flat portion of a grating is located.
該位相格子のピッチの略１／２であることを特徴とする
請求項６の光学的ローパスフィルターを有した撮影系。7. A shift amount of a phase grating between the two regions is as follows:
7. The photographing system having an optical low-pass filter according to claim 6, wherein the pitch is substantially 1/2 of the pitch of the phase grating.
垂直に入射した光束のうち位相格子の傾斜面を通過した
光束の屈折角をθｒ 、該位相格子の１次回折角をθｆ
、該位相格子の傾斜面と該基板とのなす角をθ、該位
相格子の材質の屈折率をｎ、使用波長をλ、該位相格子
の頂上平坦部の幅をＤとし、 θｒ ＝（ｎ−１）θ θｆ ＝ｓｉｎ−１（λ／Ｐ） としたとき ０．１５＜Ｄ／Ｐ＜０．３５ ０．５＜θｒ ／θｆ ＜１．４ なる条件を満足することを特徴とする請求項６又は７の
光学的ローパスフィルターを有した撮影系。8. The refraction angle of a light beam that has passed through the inclined surface of the phase grating among the light beams that are perpendicularly incident on the substrate of the optical low-pass filter is θ r , and the first-order diffraction angle of the phase grating is θ f.
Θ is the angle between the inclined surface of the phase grating and the substrate, n is the refractive index of the material of the phase grating, λ is the wavelength used, D is the width of the flat top of the phase grating, and θ r = ( n-1) When θ f = sin −1 (λ / P), it is necessary to satisfy the following condition: 0.15 <D / P <0.35 0.5 <θ r / θ f <1.4 An imaging system comprising the optical low-pass filter according to claim 6 or 7.
り、前記光学的ローパスフィルターをその位相格子方向
と該固定撮像素子の水平走査方向とのなす角をｋとした
とき ４５°＜ｋ＜７５° なる条件を満足するように配置したことを特徴とする請
求項６、７又は８の光学的ローパスフィルターを有した
撮影系。9. The imaging system has a solid-state imaging device, and when an angle between a phase grating direction of the optical low-pass filter and a horizontal scanning direction of the fixed imaging device is k, 45 ° <k. The imaging system having an optical low-pass filter according to claim 6, 7 or 8, wherein the imaging system is arranged so as to satisfy a condition of <75 °.
Priority Applications (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| JP3177199A JP2789860B2 (en) | 1991-06-21 | 1991-06-21 | Optical low-pass filter and photographing system having the same |
| US08/266,360 US5471344A (en) | 1991-03-29 | 1994-07-01 | Photographing apparatus having optical low-pass filter |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| JP3177199A JP2789860B2 (en) | 1991-06-21 | 1991-06-21 | Optical low-pass filter and photographing system having the same |
Publications (2)
| Publication Number | Publication Date |
|---|---|
| JPH04372925A JPH04372925A (en) | 1992-12-25 |
| JP2789860B2 true JP2789860B2 (en) | 1998-08-27 |
Family
ID=16026914
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| JP3177199A Expired - Fee Related JP2789860B2 (en) | 1991-03-29 | 1991-06-21 | Optical low-pass filter and photographing system having the same |
Country Status (1)
| Country | Link |
|---|---|
| JP (1) | JP2789860B2 (en) |
Families Citing this family (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| JP4345811B2 (en) | 2006-12-27 | 2009-10-14 | セイコーエプソン株式会社 | Optical element, transfer mold and imaging device |
-
1991
- 1991-06-21 JP JP3177199A patent/JP2789860B2/en not_active Expired - Fee Related
Also Published As
| Publication number | Publication date |
|---|---|
| JPH04372925A (en) | 1992-12-25 |
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