The size of the focal object in the scene is important.

一个场景的中心物体的尺寸是很重要的。

youdao

There is a simple rule that you can use to ensure you get this right: the focal object should fill about 70% of the space on the canvas (Fig. 30).

你可以用一个简单的规则来确保你得到正确的结果：中心物体应该占画布空间的大约百分之七十。

youdao

If the objective lens is closer to the compact disk than the focal length of the object lens then the cylindrical lens creates an elliptical image on the photodetector array.

如果物镜与光盘之间的距离短于物镜的焦距，柱面透镜就会使在光电探测器阵列上的成像变成椭圆影像。

youdao

It works by scanning a laser beam across an object and manipulating the reflected light to produce an extremely narrow focal plane.

ECONOMIST: The Archimedes palimpsest: Eureka! | The