Telephoto type

Japanese: telephoto type(英語表記)telephototype
Telephoto type

...The value obtained by dividing the back focus by the focal length is called the retro ratio, or inverse telephoto ratio, and the shorter the focal length of the wide-angle lens, the larger the value. (5)Telephoto type This is a method used to shorten the overall length of a lens relative to its focal length. If a convex lens system is placed in the front group and a concave lens system is placed a considerable distance away, the rear principal point will protrude further forward into the air than the front lens group. This results in a lens system with a longer focal length compared to the overall length of the lens.

*Some of the terminology that refers to "telephoto type" is listed below.

Source | Heibonsha World Encyclopedia 2nd Edition | Information

Japanese:

…バックフォーカスを焦点距離で割った値をレトロ比,あるいは逆望遠比と呼び,焦点距離の短い広角レンズほど大きな数値となる。(5)テレフォトタイプtelephoto type 焦点距離に対し,レンズの全長を短くするために用いられる方式であって,前群に凸レンズ系を置き,かなり距離を隔てて凹レンズ系を置くと,後側主点が前群レンズよりさらに前方の空中に飛び出す。こうしてレンズ全長に比べて焦点距離の長いレンズ系が得られる。…

※「telephoto type」について言及している用語解説の一部を掲載しています。

出典|株式会社平凡社世界大百科事典 第2版について | 情報

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