Star Image Test - Star Image Test

Japanese: 星像テスト - せいぞうテスト

As part of the optical inspection of astronomical telescopes, this test is conducted by directly viewing the star images at the telescope site. Starlight is a parallel beam of light, but with large-diameter telescopes, disturbance of the beam due to fluctuations in the Earth's atmosphere becomes a problem, so it is necessary to average out the fluctuations over a long period of time. The focused image of the star can be viewed through a high-magnification eyepiece or examined by taking a photograph, but it is more sensitive to compare images inside and outside the focus by shifting the image slightly from the focus. If there is spherical aberration, the blur will not be symmetrical between the inside and outside images. If there is astigmatism, the image will stretch by 90 degrees between the inside and outside images.

Source: Heibonsha World Encyclopedia, 2nd Edition Information

Japanese:

天体望遠鏡の光学検査のうち望遠鏡現場で直接星像を見て行うテスト。星の光は平行光束だが，大口径の望遠鏡では地球大気のゆらぎによる光束の乱れが問題になるので，長時間にわたってゆらぎを平均化することが必要である。星の焦点像を高倍率の接眼鏡で見るか，写真に撮って調べればよいわけだが，わずかに焦点からずらして焦点内外像を比べるほうが感度がよい。球面収差があるとボケが焦点内像と外像とで対称でなくなる。非点収差があると像ののび方が内外像で90度回る。

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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