JPS63271314A - Optical low pass filter - Google Patents
Optical low pass filterInfo
- Publication number
- JPS63271314A JPS63271314A JP62107174A JP10717487A JPS63271314A JP S63271314 A JPS63271314 A JP S63271314A JP 62107174 A JP62107174 A JP 62107174A JP 10717487 A JP10717487 A JP 10717487A JP S63271314 A JPS63271314 A JP S63271314A
- Authority
- JP
- Japan
- Prior art keywords
- light
- semi
- low
- filter
- transparent film
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Granted
Links
- 230000003287 optical effect Effects 0.000 title claims abstract description 26
- 230000001419 dependent effect Effects 0.000 claims description 2
- 239000003086 colorant Substances 0.000 abstract description 3
- 239000010408 film Substances 0.000 description 57
- 239000010410 layer Substances 0.000 description 18
- 238000010586 diagram Methods 0.000 description 10
- 230000005540 biological transmission Effects 0.000 description 9
- 239000013078 crystal Substances 0.000 description 5
- 238000002834 transmittance Methods 0.000 description 5
- 230000000694 effects Effects 0.000 description 4
- 238000003384 imaging method Methods 0.000 description 4
- 239000010453 quartz Substances 0.000 description 4
- VYPSYNLAJGMNEJ-UHFFFAOYSA-N silicon dioxide Inorganic materials O=[Si]=O VYPSYNLAJGMNEJ-UHFFFAOYSA-N 0.000 description 4
- 230000000295 complement effect Effects 0.000 description 3
- 239000000835 fiber Substances 0.000 description 3
- 230000004048 modification Effects 0.000 description 3
- 238000012986 modification Methods 0.000 description 3
- 238000001914 filtration Methods 0.000 description 2
- 238000010030 laminating Methods 0.000 description 2
- 230000010287 polarization Effects 0.000 description 2
- 239000010409 thin film Substances 0.000 description 2
- 239000012790 adhesive layer Substances 0.000 description 1
- 239000011521 glass Substances 0.000 description 1
- 238000005286 illumination Methods 0.000 description 1
- 239000000463 material Substances 0.000 description 1
- 239000012528 membrane Substances 0.000 description 1
- 238000000034 method Methods 0.000 description 1
- 239000011347 resin Substances 0.000 description 1
- 229920005989 resin Polymers 0.000 description 1
- 238000005316 response function Methods 0.000 description 1
- 238000005070 sampling Methods 0.000 description 1
- 239000007787 solid Substances 0.000 description 1
Landscapes
- Color Television Image Signal Generators (AREA)
Abstract
Description
【発明の詳細な説明】 〔産業上の利用分野〕 本発明は固体撮像素子を備えたテレビカメラ。[Detailed description of the invention] [Industrial application field] The present invention is a television camera equipped with a solid-state image sensor.
電子カメラやファイバースコープ等においてモアレを除
去するために用いられる光学的ローパスフィルターに関
する。This invention relates to an optical low-pass filter used to remove moiré in electronic cameras, fiberscopes, etc.
〔従来の技術及び発明が解決しようとする問題点〕固体
撮像素子を用いたテレビカメラでは、画素の配列のピン
チで決まるサンプリング周波数の１７２の周波数（ナイ
キスト周波数）よりも高周波の成分が画像に含まれてい
る場合、擬似信号が発生して画像を悪化させてしまうと
いう問題がある。[Problems to be solved by the prior art and the invention] In television cameras that use solid-state image sensors, images contain higher frequency components than the sampling frequency of 172 (Nyquist frequency) determined by the pinch of the pixel arrangement. If this happens, there is a problem in that pseudo signals are generated and the image deteriorates.
この擬似信号は通常モアレと呼ばれ、特に画像の中に規
則正しい配列の高周波成分が含まれていると、画像はモ
アレによって非常に見苦しいものとなってしまう。This pseudo signal is usually called moire, and especially if the image contains regularly arranged high-frequency components, the moire makes the image very unsightly.
そこで、これを除去すべく対物光学系の中で即ち固体描
像素子の前で高周波成分を予め除去しておく必要がある
が、従来はそのために複屈折素子を用いた光学的ローパ
スフィルターが開発されてきた。これは通常人工水晶板
を一枚または複数枚用いることにより構成され、水晶板
を一枚用いたもののフィルター特性即ちレスポンス関数
の絶対値ＭＴＦは第１８図に実線で示した如（ｌｃｏｓ
θ１の曲線となっている。そして、この曲線は、第１の
トラップポイントをナイキスト周波数と一敗させている
。しかし、この曲線は、ナイキスト周波数から高周波側
で急速に除去効果が弱まっていく、そこで、ナイキスト
周波数の近傍で除去効果が不足の場合は、更に同じフィ
ルター特性の水晶板を１／４波長板を挾むようにして重
ね合わせると、ＭＴＦは第１８図に点線で示した如＜Ｉ
ｃｏｓ” θ１の曲線となり、トラップポイント近傍
で曲率がかなり小になるので、良いローパス特性が得ら
れる。Therefore, in order to remove this, it is necessary to remove the high frequency component in advance in the objective optical system, that is, in front of the solid-state imaging element. Conventionally, an optical low-pass filter using a birefringent element was developed for this purpose. It's here. This is usually constructed by using one or more artificial quartz plates, and the filter characteristics, that is, the absolute value MTF of the response function when one quartz plate is used, are as shown by the solid line in Figure 18 (lcos
It is a curve of θ1. And, this curve makes the first trap point one match with the Nyquist frequency. However, this curve shows that the removal effect rapidly weakens from the Nyquist frequency to the high frequency side, so if the removal effect is insufficient near the Nyquist frequency, use a quartz plate with the same filter characteristics and a quarter-wave plate. When stacked together, the MTF becomes <I> as shown by the dotted line in Figure 18.
cos'' θ1, and the curvature becomes considerably small near the trap point, so good low-pass characteristics can be obtained.
しかしなから、対物光学系と固体撮像素子が先端部に組
み込まれている電子内視鏡にこれらの水晶板フィルター
を用いた場合、水晶板フィルターの厚みが対物光学系を
長くしてしまい、内視鏡先端部のコンパクト化にとって
大きな障害となっていた。即ち、水晶板を複数枚用いた
光学的ローパスフィルターは勿論のこと、水晶板が一枚
のものでも、その厚みの内視鏡対物光学系内に占める割
合は大きく、特に第１９図（Ａ）及び（Ｂ）に示した如
く光路中にプリズムを含む対物光学系にとってはコンパ
クト化を一層困難にするものであった。尚、第１９図に
おいて、１は対物レンズ、２は水晶板フィルター、３は
直角三角プリズム、４は固体撮像素子である。However, when these crystal plate filters are used in electronic endoscopes that have an objective optical system and a solid-state image sensor built into the tip, the thickness of the crystal plate filter makes the objective optical system longer, making the internal This has been a major obstacle to making the tip of the endoscope more compact. That is, let alone an optical low-pass filter using multiple crystal plates, even a single crystal plate accounts for a large proportion of the thickness of the endoscope objective optical system, especially as shown in Figure 19 (A). This makes it even more difficult to make the objective optical system compact as shown in (B), which includes a prism in the optical path. In FIG. 19, 1 is an objective lens, 2 is a crystal plate filter, 3 is a right triangular prism, and 4 is a solid-state image sensor.
そこで、この問題を解決する手段の一つとして、例えば
特開昭６１−２２３８０．２号公報に記載の光学フィル
ターのように近接して且つ平行に配置されたハーフミラ
−面とミラー面とから成るものが提案されている。しか
しながら、これは多重反射が生じるにもかかわらずその
点が考處されておらず、不正確であるという問題があっ
た。Therefore, as one means to solve this problem, for example, as in the optical filter described in Japanese Patent Application Laid-open No. 61-22380.2, a half mirror surface and a mirror surface are arranged close to each other in parallel. something is proposed. However, this method does not take into consideration the fact that multiple reflections occur, and has the problem of being inaccurate.
又、画像のカラー化に伴い、モザイクフィルターを撮像
素子上に配置して、読み出した信号からカラー画像を構
成する方式のテレビカメラ等が用いられるようになって
きており、最近特に限られた画素数の撮像素子で良質な
画像を得るために、従来の三原色を均一に分布して成る
モザイクフィルターに代えて、第２０図に示した如＜Ｃ
ｙ（Ｂ＋Ｇ）とＧとＹｅ （Ｒ＋Ｇ）とから成るモザイ
クフィルターを用いて輝度信号を兼ねたＧ信号が全画素
から得られるようにしたものが開発されている。即ち、
このモザイクフィルターでは、輝度信号（Ｇ信号）が全
画素から読み出され、Ｂ、Ｒ信号は夫々一つ飛びの画素
から読み出されている。In addition, as images become more colorized, television cameras and the like that construct color images from signals read out by placing a mosaic filter on the image sensor have come into use. In order to obtain high-quality images with multiple image sensors, instead of the conventional mosaic filter that uniformly distributes the three primary colors, a filter as shown in Figure 20 is used.
A mosaic filter consisting of y (B+G), G, and Ye (R+G) has been developed so that a G signal that also serves as a luminance signal can be obtained from all pixels. That is,
In this mosaic filter, the luminance signal (G signal) is read out from all pixels, and the B and R signals are read out from every other pixel.
そして、このようなモザイクフィルターに最適な光学的
ローパスフィルターが米国特許第４５７５１９３号にお
いて提案されている。このロー、＜スフイルターの特徴
は、輝度信号即ちＧ光に対してはその高い周波数帯域は
損わずにＢ、Ｒ光に対して最適なローパス特性を有して
し）ることである。An optical low-pass filter most suitable for such a mosaic filter is proposed in US Pat. No. 4,575,193. The characteristic of this low filter is that it has an optimal low-pass characteristic for B and R lights without damaging the high frequency band for the luminance signal, that is, G light.
即ち、Ｇ光の周波数帯域がＢ、Ｒ光の周波数帯域の二倍
であるなら、このローパスフィルレタ一番よ波長依存性
を有し、Ｇ光に対するロー、＜ス特性の第１トラツプポ
イントがＢ、Ｒ光のそれに比べて二倍の高周波になって
いることである。In other words, if the frequency band of G light is twice the frequency band of B and R lights, this low-pass filter has the strongest wavelength dependence, and the first trap point of the low and low characteristic for G light. is twice as high in frequency as that of B and R light.
しかしながら、このローパス特性の波長依存性は位相差
によるものであるためＲ，Ｇ、Ｂの各色の位相がなだら
かに変化し、それに応じてローパス特性もなだらかに変
化するので撮像素子のモザイクフィルターのＲ，Ｇ、Ｂ
の各波長帯域でのローパス特性が変化せず且つ波長帯間
での特性が急激に変化させられるものとならない。従っ
て、補色モザイクフィルターの緒特性に最適イヒされず
、即ち色モアレが生じ、より良い画質を得るに番よ実際
の性能としては不十分であった。However, since the wavelength dependence of this low-pass characteristic is due to the phase difference, the phase of each color of R, G, and B changes gradually, and the low-pass characteristic also changes gradually accordingly. ,G,B
The low-pass characteristics in each wavelength band do not change, and the characteristics between wavelength bands do not change suddenly. Therefore, the characteristics of the complementary color mosaic filter were not optimally achieved, that is, color moiré occurred, and the actual performance was insufficient to obtain better image quality.
本発明は、上記問題点に鑑み、対物光学系をコンパクト
に構成できると共に、ローパス特性が波長依存性を有し
且つ夫々の撮像素子に最適化されている光学的ローパス
フィルターを提供することを目的とする。In view of the above-mentioned problems, an object of the present invention is to provide an optical low-pass filter whose objective optical system can be configured compactly, whose low-pass characteristics have wavelength dependence, and whose low-pass characteristics are optimized for each image sensor. shall be.
〔問題点を解決するための手段及び作用〕本発明による
光学的ローパスフィルターは、分割若しくは反射作用を
成す少なくとも二つの略平行に配置された境界面を有す
る光学的ローパスフィルターにおいて、前記境界面のう
ち少なくとも１つは色依存性のある境界面であることに
より、多層薄膜構造であるため厚みがほとんど問題にな
らないと共に、そのローパス特性の波長依存性が波長そ
のものによるためＲ，Ｇ、Ｂの各波長帯での特性は変化
せず波長帯間での特性が急激に変化するようにしたもの
である。[Means and effects for solving the problems] The optical low-pass filter according to the present invention has at least two substantially parallel boundary surfaces that perform a dividing or reflecting function, in which At least one of them is a boundary surface with color dependence, so the thickness is hardly a problem because it is a multilayer thin film structure, and the wavelength dependence of its low-pass characteristics depends on the wavelength itself, so each of R, G, and B The characteristics within the wavelength band do not change, but the characteristics between the wavelength bands change rapidly.
以下、図示した実施例に基づき本発明の詳細な説明する
。Hereinafter, the present invention will be described in detail based on the illustrated embodiments.
第１図は第１実施例に示しており、１１は直角三角プリ
ズム４．１２は直角三角プリズム１１の斜面上に設けら
れていて第２図（Ａ）に示した如く一方向の偏光成分を
反射し且つそれと垂直な方向の偏光成分は透過する特性
を有する第１半透明膜、１３は第１半透明膜１２上に積
層された第１透過層、１４は第１透過層１３に積層され
ていて第２図（Ｂ）に示した如く、Ｇ光を反射し且つＢ
。FIG. 1 shows the first embodiment, in which 11 is a right triangular prism 4, and 12 is provided on the slope of the right triangular prism 11, and as shown in FIG. A first semi-transparent film having a property of reflecting and transmitting polarized light components in a direction perpendicular to the reflection; 13, a first transmissive layer laminated on the first semi-transparent film 12; 14, a first transmissive layer laminated on the first transmissive layer 13; As shown in Figure 2 (B), the G light is reflected and the B light is
.
Ｒ光を透過する特性を有する第２半透明膜、１５は第２
半透明膜１４上に積層された第２透過庖、１６は透過層
１５上に積層されていて第２図（Ｃ）の曲線ａで示した
如＜Ｂ、Ｒ光を反射し且つＧ光を透過する特性を有する
第３半透明膜である。a second semi-transparent film having a property of transmitting R light; 15 is a second semi-transparent film;
A second transmission layer 16 laminated on the semi-transparent film 14 is laminated on the transmission layer 15 and reflects the B and R lights and reflects the G light as shown by curve a in FIG. 2(C). This is a third semi-transparent film having a transmitting property.
尚、第３半透明膜１６の代わりに第２図（Ｃ）の曲線す
に示した如（全ての光をほとんど反射する反射膜でも良
い。又、全反射面でも良い、そして、第１透過層１３の
厚みは第１半透明膜１２で反射したＲ、Ｇ、Ｂ光と第２
半透明膜１４で反射したＧ光とのなす間隔ｄ１が固体撮
像素子の画素間隔の１／２となるように設定され、第１
透過層１３と第２透過層１５との厚みの和は第１半透明
膜１２で反射したＲ、Ｇ、Ｂ光と第３半透明膜１６で反
射したＢ、Ｒ光とのなす間隔ｄ２が固体↑最像素子の画
素間隔となるように設定されている。これらの間隔ｄ、
、ｄ、は画素間隔に合わせて数〜数十μとなっており、
数μ以上であれば通常の白色光源照明や自然光下では干
渉による反射光の色づきは生じないので問題は無い。又
、第１及び第２透過層１３及び１５は接着剤層、薄いガ
ラス板。Note that instead of the third semitransparent film 16, a reflective film that reflects almost all the light may be used (as shown in the curve in FIG. 2C), or a total reflection surface may be used. The thickness of the layer 13 is such that the R, G, and B light reflected by the first semitransparent film 12 and the second
The interval d1 between the G light reflected by the semi-transparent film 14 is set to be 1/2 of the pixel interval of the solid-state image sensor, and the first
The sum of the thicknesses of the transparent layer 13 and the second transparent layer 15 is determined by the distance d2 between the R, G, and B lights reflected by the first semitransparent film 12 and the B and R lights reflected by the third semitransparent film 16. Solid ↑ is set to be the pixel interval of the most image element. These intervals d,
, d, is several to several tens of microns depending on the pixel spacing,
If it is several μ or more, there is no problem because the reflected light will not be colored due to interference under normal white light source illumination or natural light. Further, the first and second transmission layers 13 and 15 are adhesive layers and thin glass plates.
蒸着物質膜、樹脂膜等から成っている。It consists of a vapor deposited material film, a resin film, etc.
本実施例は上述の如く構成されているから、Ｇ光は間隔
ｄ、 （ｉｉ！素の１／２ピツチンだけ離れた二点に
分離され、Ｂ、Ｒ光は間隔ｄ、（画素の１ピツチ）だけ
離れた二点に分離される。従って、本実施例全体のフィ
ルター特性は、第３図に示した如＜、Ｂ、Ｒ光に対して
は最初のトラップポイントを１／４ｆｓ（ｆｓは空間周
波数）に、Ｇ光に対しては最初のトラップポイントを１
／ ２ ｆ ｓに夫々することができるので、Ｇ先部
ち輝度信号の帯域を損なうことなく、色信号即ちＢ、Ｒ
光の高周波成分を押さえることができる。Since this embodiment is configured as described above, the G light is separated into two points separated by the interval d, (ii! 1/2 pitch of the pixel), and the B and R lights are separated by the interval d, (1 pitch of the pixel). ).Therefore, the filter characteristics of the entire embodiment are as shown in FIG. (spatial frequency), and for G light, set the first trap point to 1.
/2fs, respectively, so the chrominance signal, that is, B, R
It can suppress high frequency components of light.
以上、本実施例のローパス特性について説明したが、本
実施例はわずか数〜数十μの多層薄膜構造であるため厚
みがほとんど問題にならず、対物光学系をコンパクトに
構成することができる。又、このローパス特性の波長依
存性が波長そのものによるため第２図（Ｂ）、（Ｃ）に
示した如＜Ｒ。The low-pass characteristics of this embodiment have been described above, but since this embodiment has a multilayer thin film structure of only a few to several tens of microns, the thickness is hardly a problem, and the objective optical system can be configured compactly. Moreover, since the wavelength dependence of this low-pass characteristic depends on the wavelength itself, <R> as shown in FIGS. 2(B) and (C).
Ｇ、Ｈの各波長帯での特性は変化せず波長帯間で急激に
変化する。従って、このローパス特性は、例えば第４図
に示した如き特性の補色モザイクフィルターの該特性に
最適化されたもの即ち色モアレを非常に少なくできるも
のとなる。The characteristics in each wavelength band of G and H do not change but change rapidly between the wavelength bands. Therefore, this low-pass characteristic is optimized for the characteristic of a complementary color mosaic filter as shown in FIG. 4, that is, it can greatly reduce color moiré.
尚、膜のフィルター特性を変化させることで、つまり波
長の帯域幅や波長をモザイクフィルターの各Ｒ，Ｇ、Ｂ
の波長域に対して変えることでフィルター特性を自由に
変えることもできる。In addition, by changing the filter characteristics of the film, that is, the wavelength bandwidth and wavelength can be adjusted to each R, G, and B of the mosaic filter.
The filter characteristics can also be freely changed by changing the wavelength range.
第５図は第２実施例を示しており、これは第１半透明膜
１２′が偏光特性を有しない点以外は第１実施例と同じ
構成を有するものである。FIG. 5 shows a second embodiment, which has the same structure as the first embodiment except that the first semitransparent film 12' does not have polarizing properties.
本実施例の場合複数の膜間での多重反射を考慮する必要
がある。In the case of this embodiment, it is necessary to consider multiple reflections between a plurality of films.
まず、第１半透明膜１２′に入射した白色光はその一部
が反射し且つ他部が透過する。そして、反射光は第６図
の番号Ｏの白色光線（Ｂ、Ｇ。First, part of the white light incident on the first semi-transparent film 12' is reflected and the other part is transmitted. The reflected light is the white light ray number O in FIG. 6 (B, G).
Ｒ）として固体撮像素子の受像面に達する。一方、第１
半透明膜１２′を透過した光のうちＧ光は第２半透明膜
１４で反射した後第１及び第２半透明膜１２’、１４間
で多重反射し、第５図に示した番号１，２，３．・・・
・・−・・・・の光線が受像面に達する。R) reaches the image receiving surface of the solid-state image sensor. On the other hand, the first
Of the light that has passed through the semi-transparent film 12', the G light is reflected by the second semi-transparent film 14 and then multiple-reflected between the first and second semi-transparent films 12' and 14, resulting in a light beam numbered 1 shown in FIG. , 2, 3. ...
The light rays of... reach the image receiving surface.
この場合各光線は間隔ｄ、ずつ離れ且つ光量を減衰させ
ながら点像を結ぶ。又、Ｂ、Ｒ光は第２半透明膜１４を
透過し第３半透明膜１６で反射した後第１及び第３半透
明膜１２′、１６１’Ｂｌで多重反射し、第５図に示し
た番号２．４．−・・・・・・・−の光線が受像面に達
する。この場合、各光線は間隔ｄ！ずつ離れ且つ光量を
減衰させながら点像を結ぶ。そこで、第１半透明膜１２
゛の透過率をＴ、反射率を（１−Ｔ）とした時、各点像
の強度は第６図の表の如くになり、点像の強度分布をグ
ラフに表わすと第７図に示した如くになる。In this case, each light ray is separated by a distance d and forms a point image while attenuating the amount of light. Further, the B and R lights are transmitted through the second semi-transparent film 14, reflected by the third semi-transparent film 16, and then subjected to multiple reflections by the first and third semi-transparent films 12' and 161'Bl, as shown in FIG. Number 2.4. The light rays of -......- reach the image receiving surface. In this case, each ray is spaced d! A point image is formed while moving apart and attenuating the amount of light. Therefore, the first semi-transparent film 12
When the transmittance of ゛ is T and the reflectance is (1-T), the intensity of each point image is as shown in the table in Figure 6, and the intensity distribution of the point image is graphed as shown in Figure 7. It becomes like that.
そこで、多重反射を含めた点像の強度分布をフーリエ変
換してフィルターリング特性を求めると、＝ （１−Ｔ
） ＋７ｔΣ （１−Ｔ） −ｃｏｓ２πｋ（ｍｄ）
となる。ここで、Ｔをパラメータにし、ｋ値を横軸にと
って特性をグラフに表わすと第８図に示した如くになる
。Therefore, when the intensity distribution of point images including multiple reflections is Fourier transformed to find the filtering characteristics, = (1-T
) +7tΣ (1-T) -cos2πk(md)
becomes. Here, if the characteristics are expressed in a graph with T as a parameter and the k value on the horizontal axis, the result will be as shown in FIG.
第８図のグラフより、ローパスフィルターとして適切な
のは、Ｔ ＝ ０．５５〜０．９５の範囲であることが
明らかである。特に、性能が良いのが、Ｔ−〇６６〜０
．８の範囲である。Ｔ＝０．６〜０．８の範ｄ ４ｄ
さえており、一枚構成の水晶板フィルターの特性を大巾
に止まった高性能なものとなっている。これは第１実施
例とは異なり、多重反射を採用することにより実現でき
た特性である。From the graph in FIG. 8, it is clear that T = 0.55 to 0.95 is suitable as a low-pass filter. Particularly good performance is T-〇66~0
．． The range is 8. T=0.6 to 0.8, d 4d , is maintained, and the filter has a high performance that greatly exceeds the characteristics of a single-piece quartz plate filter. Unlike the first embodiment, this characteristic was achieved by employing multiple reflections.
第９図は第３実施例を示しており、これは直角三角プリ
ズム１１の斜面上に白色光を二分割し且つＩＲ（赤外）
光を透過する第１半透明膜１７゜第１透過層１８．Ｇ光
を反射し且つＢ、Ｒ，ＩＲ光を透過する第２半透明膜１
９．第２透過Ｎ２０゜Ｂ光を反射し且つＲ，ＩＲ光を透
過する第３半透明膜２１．第３透過層２２．Ｒ光を反射
しＩＲ光を透過する第４半透明膜２３を順次積層して成
るものであり、Ｇ、Ｂ、Ｒ光の分離間隔ｄ、、ｄ、。FIG. 9 shows a third embodiment, in which white light is divided into two on the slope of a right triangular prism 11, and IR (infrared)
First semi-transparent film 17° that transmits light; first transparent layer 18. Second semi-transparent film 1 that reflects G light and transmits B, R, and IR light
9. A third semi-transparent film 21 that reflects the second transmitted N20°B light and transmits the R and IR light. Third transmission layer 22. The fourth semi-transparent film 23 that reflects R light and transmits IR light is sequentially laminated, and the G, B, and R lights are separated at intervals d, d,.
ｄ、が全て異なっている。これは、固体撮像素子上のモ
ザイクフィルターの色配置においてＧ、Ｂ。d, are all different. This is G and B in the color arrangement of the mosaic filter on the solid-state image sensor.
Ｒの各間隔が全て異なる場合に適合する。This applies when the intervals of R are all different.
本実施例は、全ての半透明膜１７，１９，２１゜２３が
ＩＲ透過特性を有しているので、固体撮像素子への有害
光が除去されるという利点がある。This embodiment has the advantage that all the semitransparent films 17, 19, 21, and 23 have IR transmission characteristics, so that harmful light to the solid-state image pickup device is removed.
尚、膜の特性をモザイクフィルターの波長特性に対して
変える、つまり波長や帯域幅を変えたり各色ごと透過反
射率を変えることで自由に様々な特性を得ることができ
る。Note that various characteristics can be freely obtained by changing the characteristics of the film relative to the wavelength characteristics of the mosaic filter, that is, by changing the wavelength or bandwidth, or by changing the transmission/reflectance for each color.
又、第１半透明膜１７には、第１実施例で示したような
偏光特性を持つ半透明膜を用いても良いし、第２実施例
で示したような偏光特性を持たない半透明膜を用いても
良い、但し、その場合のローパス特性は第１実施例及び
第２実施例に夫々示した特性となる。Further, the first semi-transparent film 17 may be a semi-transparent film having polarizing properties as shown in the first embodiment, or a semi-transparent film having no polarizing properties as shown in the second embodiment. A film may be used, however, the low-pass characteristics in that case will be the characteristics shown in the first embodiment and the second embodiment, respectively.
第１０図は第４実施例を示しており、これは直角三角プ
リズム１１の斜面上に白色光を分割する第１半透明膜２
４．透過層２５．Ｒ，Ｂ光は反射し且つＧ光を透過する
第２半透明膜２６を順次積層して成るものであり、Ｇ光
に対するローパス特性は持たず、Ｒ，Ｂ光に対してだけ
ローパス特性を有する。これは、固体撮像素子の画素数
が大幅に増えた場合に適合する。FIG. 10 shows a fourth embodiment, in which a first semi-transparent film 2 splitting white light onto the slope of a right triangular prism 11 is shown.
4. Transparent layer 25. It is made by sequentially laminating the second semi-transparent film 26 that reflects the R and B lights and transmits the G light, and does not have a low-pass characteristic for the G light, but has a low-pass characteristic only for the R and B lights. . This is suitable when the number of pixels of the solid-state image sensor increases significantly.
尚、第１半透明膜２４には、第１実施例で示したような
偏光特性を持つ半透明膜を用いても良いし、第２実施例
で示したような偏光特性を持たない半透明膜を用いても
良い、但し、その場合のローパス特性は第１実施例及び
第２実施例に夫々示した特性となる。Note that the first semi-transparent film 24 may be a semi-transparent film with polarizing properties as shown in the first embodiment, or a semi-transparent film without polarizing properties as shown in the second embodiment. A film may be used, however, the low-pass characteristics in that case will be the characteristics shown in the first embodiment and the second embodiment, respectively.
上記第１乃至第４実施例のローパスフィルターＬＰは、
実際には第１１図（Ａ）及び（Ｂ）に示した如く配置さ
れる。但し、第１１図（Ａ）のようにレンズ系と撮影面
の間でなくレンズ系の内部に配置した場合は、光学系の
倍率を考慮して撮像面で適切なずれ量ｄになるように厚
さを選ぶ必要がある。又、二つのローパスフィルターＬ
Ｆを第１２図に示した如く配置すれば、二次元的なロー
パスフィルター特性をもたせることが可能である。The low-pass filters LP of the first to fourth embodiments are as follows:
Actually, they are arranged as shown in FIGS. 11(A) and 11(B). However, if it is placed inside the lens system instead of between the lens system and the imaging surface as shown in Figure 11 (A), take into account the magnification of the optical system and make sure that the appropriate amount of deviation d is achieved on the imaging surface. You need to choose the thickness. Also, two low-pass filters L
If F is arranged as shown in FIG. 12, it is possible to provide two-dimensional low-pass filter characteristics.
第１３図は第５実施例を示しており、これは直角三角プ
リズム１１の斜面上にＧ光は反射し且つＢ、Ｒ光は二分
割する半透明１１１２７．ｉ３過層２８゜Ｂ、Ｒ光を反
射する反射膜２９を順次積層して成る第１フィルターＦ
、と、直角三角プリズム１１の斜面上にＢ、Ｒ光は反射
し且つＧ光は二分割する半透明膜３０．透過層３１．Ｇ
光を反射する反射膜３２を順次積層して成る第２フイル
ターＦ２と対向配置せしめて成るものである。FIG. 13 shows a fifth embodiment, in which the G light is reflected on the slope of the right triangular prism 11, and the B and R lights are divided into two by a translucent 11127. i3 overlayer 28°B, first filter F consisting of sequentially laminated reflective films 29 that reflect R light;
, and a semitransparent film 30 that reflects the B and R lights on the slope of the right triangular prism 11 and divides the G light into two. Transparent layer 31. G
It is arranged opposite to a second filter F2 formed by successively laminating reflective films 32 that reflect light.
尚、半透明膜２７．３０を偏光特性を有し且つ透過率１
反射率が５０％、５０％であるものにすれば、多重反射
は生じない。一方、半透明膜２７゜３０を偏光特性のな
いものにすれば多重反射が生じ、透過率１反射率の比率
を選ぶことにより良いローパス特性を得ることができる
。In addition, the semi-transparent film 27.30 has polarizing properties and has a transmittance of 1.
If the reflectance is 50%, multiple reflection will not occur. On the other hand, if the semitransparent film 27.30 has no polarizing properties, multiple reflections will occur, and by selecting a ratio of transmittance to reflectance, good low-pass characteristics can be obtained.
本実施例は、第１４図（Ａ）、（Ｂ）、（Ｃ）に示した
如く配置しても良い。This embodiment may be arranged as shown in FIGS. 14(A), 14(B), and 14(C).
第１５図（Ａ）と（Ｂ）は夫々第１及び第２実施例の変
形例と第５実施例の変形例を示しており、これらは夫々
ダハプリズム３３のダハ面の片側及び両側にフィルタ一
部分を設けて成るものである。FIGS. 15A and 15B show a modification of the first and second embodiments and a modification of the fifth embodiment, respectively. It is made up of the following.
第１６図は第６実施例を示しており、これは一対の直角
三角プリズム１１．１１の間に、白色光を二分割する第
１半透明膜３４．第１透過層３５゜０光を二分割し且つ
Ｂ、Ｒ光を透過する第２半透明膜３６．第２透過７１３
７．Ｂ、Ｒ光を二分割し且つＧ光を透過する第３半透明
膜３８を順次積層して成るものである。そして、第１半
透明膜３４を偏光特性を有するものにすれば多重反射が
生じないので、第１６図下方にはローパスフィルター特
性を有し且つ第１６図右方（例えばファインダー側）に
はローパスフィルター特性を有しないものとなる。一方
、第１半透明膜３４を偏光特性を有しないものにすれば
多重反射が生じるので、第１６図下方と右方の両側にロ
ーパスフィルター特性が生じるものとなる。FIG. 16 shows a sixth embodiment, which consists of a first semi-transparent film 34.1 which divides white light into two parts between a pair of right triangular prisms 11.11. 1st transparent layer 35°; second semi-transparent film 36 which divides the light into two and transmits the B and R lights; Second transmission 713
7. A third semi-transparent film 38 that divides the B and R lights into two and transmits the G light is sequentially laminated. If the first semi-transparent film 34 is made to have polarization characteristics, multiple reflections will not occur, so the lower part of FIG. 16 has low-pass filter characteristics, and the right part of FIG. It has no filter characteristics. On the other hand, if the first semi-transparent film 34 is made to have no polarization characteristics, multiple reflections will occur, so that low-pass filter characteristics will occur on both sides of the lower and right sides of FIG. 16.
本実施例のローパスフィルターＬＦは、第１７図に示し
た如く、ファイバースコープ接眼部３９に外付けして用
いるテレビカメラ４０の撮像レンズ４１と接眼レンズ４
２との間に配置され、ファイバー束の出射端面のファイ
バ一端部の規則的並びと固体撮像素子４の受像面の画素
の規則的並びとの間で生じるモアレを除去するのに用い
られる。The low-pass filter LF of this embodiment, as shown in FIG.
2, and is used to remove moiré that occurs between the regular arrangement of one end of the fibers on the output end face of the fiber bundle and the regular arrangement of pixels on the image receiving surface of the solid-state image sensor 4.
上述の如く、本発明による光学的ローパスフィルターは
、対物光学系番コンパクトに構成できて内視鏡対物光学
系に好適であると共に、ローパス特性が波長依存性を有
し且つ最適化されて色モアレを非常に少なくできるとい
う実用上重要な利点を有している。又、多重反射式にす
ればフィルター特性が数段改善されたものにすることが
でき、更に複数個用いることにより二次元的なフィルタ
ー特性を得ることができるなどの利点も有している。As described above, the optical low-pass filter according to the present invention has a compact objective optical system structure and is suitable for an endoscope objective optical system, and also has wavelength-dependent low-pass characteristics and is optimized to prevent color moiré. It has the important practical advantage of being able to significantly reduce the amount of Further, if a multiple reflection type is used, the filter characteristics can be improved by several steps, and by using a plurality of filters, two-dimensional filter characteristics can be obtained.
第１図は本発明による光学的ローパスフィルターの第１
実施例の断面図、第２図（Ａ）乃至（Ｃ）は第１実施例
の各膜の透過率特性を示す図、第３図は第１実施例のフ
ィルター特性を示す図、第４図は補色モザイクフィルタ
ーの透過率特性を示す図、第５図は第２実施例の断面図
、第６図及び第７図は夫々第２実施例の各点像の強度を
示す表及び強度分布を示すグラフ、第８図は第２実施例
のフィルターリング特性を示すグラフ、第９図及び第１
０図は夫々第３及び第４実施例の断面図、第１１図（Ａ
）、（Ｂ）及び第１２図は第１乃至第４実施例の実際の
配置図、第１３図は第５実、轡例の断面図、第１４図（
Ａ）乃至（Ｃ）は第５実施例の配置図、第１５図（Ａ）
及び（Ｂ）は夫々第１．第２実施例及び第５実施例の各
変形例の断面図、第１６図は第６実施例の断面図、第１
７図は第６実施例の実際の配置図、第１８図は従来例の
フィルター特性を示す図、第１９図は従来例の実際の配
置図、第２０図はモザイクフィルターの色配置図である
。
１・・・・対物光学系、４・・・・固体撮像素子、１１
・・・・直角三角プリズム、１２．１２’、１７，２４
．３４・・・・第１半透明膜、１３，１８．３５−９・
・第１透過層、１４，１９，２６．３６・・、・第２半
透明膜、１５，２０．３７・・・・第２透過層、１６．
２１．３８・・・・第３半透明膜、２２・・・・第３透
過層、２３・・・・第４半透明膜、２５，２８．３１・
・・・透過層、２７．３０・・・・半透明膜、２９゜３
２・・・・反射膜、３３・・・・ダハプリズム、３９・
・・・ファイバースコープ接眼部、４０・・・・テレビ
カメラ、４１・・・・撮像レンズ、４２・・・・接眼レ
ンズ。
第３図
ＩＦ５図
４００ ５００ ６ＣＸ） χ）Ｏｎｍ３皮（ｋ
第５図
オフ図
ニー ざ Ｃｇ ｇ Ｃｇ Ｌ″′第
１２図
第１３図
第１４図
？１５図
１−１６図
第１７図
１Ｐ１８図
ブンア″ルアｎ俄（（FIG. 1 shows a first diagram of an optical low-pass filter according to the present invention.
A cross-sectional view of the example, FIG. 2 (A) to (C) are diagrams showing the transmittance characteristics of each membrane of the first example, FIG. 3 is a diagram showing the filter characteristics of the first example, and FIG. 4 is a diagram showing the transmittance characteristics of the complementary color mosaic filter, FIG. 5 is a sectional view of the second embodiment, and FIGS. 6 and 7 are a table showing the intensity of each point image and the intensity distribution of the second embodiment. FIG. 8 is a graph showing the filtering characteristics of the second embodiment, FIG. 9 and FIG.
Figure 0 is a sectional view of the third and fourth embodiments, and Figure 11 (A
), (B), and FIG. 12 are actual layout diagrams of the first to fourth embodiments, FIG. 13 is a cross-sectional view of the fifth embodiment, and FIG. 14 (
A) to (C) are layout diagrams of the fifth embodiment, FIG. 15 (A)
and (B) are respectively No. 1. 16 is a sectional view of each modification of the second embodiment and the fifth embodiment, and FIG. 16 is a sectional view of the sixth embodiment.
Figure 7 is an actual layout diagram of the sixth embodiment, Figure 18 is a diagram showing filter characteristics of a conventional example, Figure 19 is an actual layout diagram of a conventional example, and Figure 20 is a color layout diagram of a mosaic filter. . 1... Objective optical system, 4... Solid-state image sensor, 11
...Right triangular prism, 12.12', 17,24
．． 34...first semi-transparent film, 13,18.35-9.
-First transmission layer, 14,19,26.36..., -Second semi-transparent film, 15,20.37...Second transmission layer, 16.
21.38...Third semi-transparent film, 22...Third transparent layer, 23...Fourth semi-transparent film, 25,28.31...
... Transparent layer, 27.30 ... Semi-transparent film, 29°3
2... Reflective film, 33... Roof prism, 39...
...Fiber scope eyepiece, 40...TV camera, 41...Imaging lens, 42...Eyepiece. Figure 3 IF5 Figure 400 500 6CX) ″Lua n 俄((
Claims (1)
配置された境界面を有する光学的ローパスフィルターに
おいて、前記境界面のうち少なくとも一つは色依存性の
ある境界面であることを特徴とする光学的ローパスフィ
ルター。An optical low-pass filter having at least two substantially parallel boundary surfaces that perform a dividing or reflecting function, characterized in that at least one of the boundary surfaces is a color-dependent boundary surface. low pass filter.
Priority Applications (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| JP62107174A JP2539424B2 (en) | 1987-04-30 | 1987-04-30 | Optical low pass filter |
| US07/536,958 US5237446A (en) | 1987-04-30 | 1990-06-12 | Optical low-pass filter |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| JP62107174A JP2539424B2 (en) | 1987-04-30 | 1987-04-30 | Optical low pass filter |
Publications (2)
| Publication Number | Publication Date |
|---|---|
| JPS63271314A true JPS63271314A (en) | 1988-11-09 |
| JP2539424B2 JP2539424B2 (en) | 1996-10-02 |
Family
ID=14452350
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| JP62107174A Expired - Lifetime JP2539424B2 (en) | 1987-04-30 | 1987-04-30 | Optical low pass filter |
Country Status (1)
| Country | Link |
|---|---|
| JP (1) | JP2539424B2 (en) |
Cited By (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| JP2008046162A (en) * | 2006-08-10 | 2008-02-28 | Canon Inc | Reflecting optical element and imaging device |
-
1987
- 1987-04-30 JP JP62107174A patent/JP2539424B2/en not_active Expired - Lifetime
Cited By (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| JP2008046162A (en) * | 2006-08-10 | 2008-02-28 | Canon Inc | Reflecting optical element and imaging device |
Also Published As
| Publication number | Publication date |
|---|---|
| JP2539424B2 (en) | 1996-10-02 |
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