The focal plane of the light is 200 feet above mean sea level, and in clear weather it should be seen at a distance of 23 nautical miles.
灯光的焦平面位于平均海平面以上200尺，如天气清朗，远至23海里的水域也能看见。
From the theory of light diffraction and geometrical optics, aperture diffraction near the focal plane of microscope objectives and imaging on the image plane are studied.
从光的衍射理论和几何成象理论出发，分析研究了显微物镜焦平面附近小孔光栏的衍射和象平面位置上的成象。
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