Why is the lens of a camera and a projection apparatus made movable?

Since the distance from the projection device to the screen can be different, then to obtain a clear image of the object on the screen, move the lens, thus changing the distance from the object to the lens. Also, a clear image on the film of the camera is achieved by changing the distance from the film to the lens.

Remember: The process of learning a person lasts a lifetime. The value of the same knowledge for different people may be different, it is determined by their individual characteristics and needs. Therefore, knowledge is always needed at any age and position.