The searchlight lens does not imitate (u = f) why can we use, how can we control the distance and distance
And u = f (that is, the lamp is in the focal position)
But the light emitted by the bulb is irradiated to the target area to be irradiated through the lens.
The purpose of the searchlight is not imaging,
Light emitted by the light after the lens refraction, just parallel light,
Can increase the brightness of light, easy to observe.
