Cassegrain focus - Cassegrain focus

…Newtonian focus is a focus where a diagonal mirror inclined at 45 degrees to the optical axis is placed in front of the principal focus to guide the image to the side. A convex mirror is placed in front of the principal focus to extend the composite focal length and form a star image behind the primary mirror through a hole in the center of the primary mirror, which is called a Cassegrain focus. A 45-degree diagonal mirror is placed midway between the two and forms an image on the declination or horizontal axis of the telescope, which is called a Nasmyth focus. Furthermore, a Coude focus is a focus where several plane mirrors are used to guide the starlight outside the telescope through the polar or vertical axis and form an image on a fixed point. …

*Some of the terminology explanations that mention "Cassegrain focus" are listed below.

Source | Heibonsha World Encyclopedia 2nd Edition | Information

…ニュートン焦点は主焦点の手前に光軸に対し45度傾いた斜鏡を置いて像面を側方に導いたものである。主焦点の手前に凸面鏡を置いて合成焦点距離を延長し，主鏡中心の穴を通して主鏡の後に星像を結ばせるのをカセグレン焦点，その途中に45度の斜鏡を置き，望遠鏡の赤緯軸または水平軸上に結像させるのをナスミス焦点という。さらに数枚の平面鏡を使って極軸または垂直軸を通して星の光を望遠鏡外に導き，固定点に結像させるのをクーデ焦点という。…

※「カセグレン焦点」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