Reflecting telescopes

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  • Reflecting telescopes
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  • Catoptric telescopes
  • Reflector telescopes
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Abstract from DBPedia
    A reflecting telescope (also called a reflector) is a telescope that uses a single or a combination of curved mirrors that reflect light and form an image. The reflecting telescope was invented in the 17th century by Isaac Newton as an alternative to the refracting telescope which, at that time, was a design that suffered from severe chromatic aberration. Although reflecting telescopes produce other types of optical aberrations, it is a design that allows for very large diameter objectives. Almost all of the major telescopes used in astronomy research are reflectors. Many variant forms are in use and some employ extra optical elements to improve image quality or place the image in a mechanically advantageous position. Since reflecting telescopes use mirrors, the design is sometimes referred to as a catoptric telescope. From the time of Newton to the 1800s, the mirror itself was made of metal – usually speculum metal. This type included Newton's first designs and even the largest telescopes of the 19th century, the Leviathan of Parsonstown with a 1.8 meter wide metal mirror. In the 19th century a new method using a block of glass coated with very thin layer of silver began to become more popular by the turn of the century. Common telescopes which led to the Crossley and Harvard reflecting telescopes, which helped establish a better reputation for reflecting telescopes as the metal mirror designs were noted for their drawbacks. Chiefly the metal mirrors only reflected about 2⁄3 of the light and the metal would tarnish. After multiple polishings and tarnishings, the mirror could lose its precise figuring needed. Reflecting telescopes became extraordinarily popular for astronomy and many famous telescopes, such as the Hubble Space Telescope, and popular amateur models use this design. In addition, the reflection telescope principle was applied to other electromagnetic wavelengths, and for example, X-ray telescopes also use the reflection principle to make image-forming optics.

    レフ板（レフばん、英: board reflector）は、撮影の被写体に光を反射させる板。乱反射鏡の一種である。主に写真、映画、テレビの撮影で用いられる。レフは反射を表すreflexのドイツ語読み、レフレックスから。 カメラを用いた撮影を行う場合、太陽光や人工照明などの光源があり、それからの直接光以外に、その光線を反射させて間接光として利用することがある。そのためには一定の反射率を持つ素材を扱いやすい形状に加工する必要がある。 シーツのような白い布を用いたり、カポックと称される発泡スチロール板を利用することもあるが、大きくなればロケーションなどでの可搬性や機動力は乏しくなり、それに向くものが既製品のレフ板である。 反射材となる布を金属製または樹脂製の枠に張り付けたもので、分解或いは折り畳むことが可能なものが多い。円形の丸レフは枠が容易に変形し、ねじって折り畳むことが出来る。四角形のロールレフは枠が4本の中空パイプを組み立てたもので、不要の際には枠を分解して反射材であった布で巻き取って持ち運びが出来る。 布は白色、銀色、金色、青銀色などの反射率の高いものの他、薄手の白色である程度光を透過させる素材のものも用いられる。また片面ごとに色が異なるものもある。 透過素材のものは強い太陽光線を遮り、直射日光を柔らかい光に変えるために用いるディフューザの役割を果たす。或いは不透明なものを用いて被写体に影を作ることもある。 本来の用途とは異なるが、フレアやゴーストを引き起こす有害光を遮るためにカメラにかざす使用法もある。ハレ切りとも呼ばれる。 野外でのポートレイト撮影を行う際の一般的な使用方法としては、逆光の状態になるよう被写体を太陽を背にして立たせ、後方からの光線を前方で反射させて、顔及び前面を照らす。これにより順光状態で発生する強い陰影を防ぐことが出来る。更に瞳に映り込むレフ板がキャッチライトとなり、表情が活き活きとしてみえる効果もある。なおレフ板の形状がそのままキャッチライトの形となるため、それにより撮影された映像の印象が異なる。 反射面の色の選択は、光線状態や撮影意図によって行う。反射率の高い銀色系は曇天時の集光に役立つ反面、晴天時では強すぎ、映像的にはコントラストが強くなり、またモデルにとっては眩しく瞳孔が縮まってしまう。その際は反射率の低い白色系を用い、低コントラストの柔らかい光線とするのが良いとされる。森林など周りからの照り返し光の影響で緑色の色かぶりが起きることがあるが、それを打ち消すために金系を用いるテクニックもある。 同じレフレックスという言葉が語源に有る一眼レフカメラの内蔵部品、がレフ板と呼ばれるケースが有るが、誤用である。レフ板が間接光を作るものであるのに対し、はフィルムに結像する光をそのままファインダーに伝えるためのものであり、用途が全く異なる。

    (Source: http://dbpedia.org/resource/Reflecting_telescope)

    A reflecting telescope (also called a reflector) is a telescope that uses a single or a combination of curved mirrors that reflect light and form an image. The reflecting telescope was invented in the 17th century by Isaac Newton as an alternative to the refracting telescope which, at that time, was a design that suffered from severe chromatic aberration. Although reflecting telescopes produce other types of optical aberrations, it is a design that allows for very large diameter objectives. Almost all of the major telescopes used in astronomy research are reflectors. Many variant forms are in use and some employ extra optical elements to improve image quality or place the image in a mechanically advantageous position. Since reflecting telescopes use mirrors, the design is sometimes referred to as a catoptric telescope. From the time of Newton to the 1800s, the mirror itself was made of metal – usually speculum metal. This type included Newton's first designs and even the largest telescopes of the 19th century, the Leviathan of Parsonstown with a 1.8 meter wide metal mirror. In the 19th century a new method using a block of glass coated with very thin layer of silver began to become more popular by the turn of the century. Common telescopes which led to the Crossley and Harvard reflecting telescopes, which helped establish a better reputation for reflecting telescopes as the metal mirror designs were noted for their drawbacks. Chiefly the metal mirrors only reflected about 2⁄3 of the light and the metal would tarnish. After multiple polishings and tarnishings, the mirror could lose its precise figuring needed. Reflecting telescopes became extraordinarily popular for astronomy and many famous telescopes, such as the Hubble Space Telescope, and popular amateur models use this design. In addition, the reflection telescope principle was applied to other electromagnetic wavelengths, and for example, X-ray telescopes also use the reflection principle to make image-forming optics.

    反射望遠鏡（はんしゃぼうえんきょう、Reflecting telescope ）は、鏡を組み合わせた望遠鏡である。

    (Source: http://dbpedia.org/resource/Reflecting_telescope)