在使用或选购手电筒时，有时须旋转手电筒的头帽，使聚光集中或检验聚光能否集中．其中的奥密是什么呢？从凹镜焦点发出的光被凹镜反射以后，将成为平行光．手电筒的回光碗相当于凹镜．旋转手电筒的头帽时，回光磁随着移动，从而改变电珠（灯泡）在回光碗前的位置．兰灯丝恰好 When using or selecting a flashlight, it is sometimes necessary to rotate the headlight of the flashlight to focus the concentration or focus the inspection. Which is the Omi? After the light from the concave mirror is reflected by the concave mirror, it will become parallel light. The flashlight bowl is equivalent to a concave mirror. When rotating the headlamp of the flashlight, the return magnetism moves, thereby changing the position of the electric ball (light bulb) before the return light bowl. Lan Lan is exactly