The diameter of a sphere is four times the focal length of a concave mirror cut from it.
凹面镜如果是从圆球上切下来的，圆球的直径会是凹面镜焦距的四倍。
2
The calculating results showed that the optimized geometry of soldering fillet is a concave shape in which the extruding length of the soldering fillet is a little more than the gap height.