actual l image point 实际像点
However, for the actual optical system, its point image become a speckle because of diffraction of light and aberration.
对于实际光学系统，由于光的衍射和像差，使所成的点像为一弥散斑。
In actual practice a brighter image is obtained by using a broad, rather than a point, source along with a substage condenser.
在实际工作中，不是用点光源而是用一个扩展光源加一个台下聚光镜以得到一个较亮的象。
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