Modern camera. Optical lenses used in cameras have variable focal lengths. When the object distance changes, it can still be obtained without changing the distance (image distance) from the lens to th

Modern camera. Optical lenses used in cameras have variable focal lengths. When the object distance changes, it can still be obtained without changing the distance (image distance) from the lens to the substrate. Under normal circumstances, if the focal length changes, the image distance will also change.

But some zoom lenses are quadruped group, objective lens group, zoom group, compensation group and rear fixed group. By moving the zoom group and compensation group, the focal length of the lens can be changed without changing the position of the image plane.

When the object distance increases, the imaging picture does not decrease and the image plane does not move, which can be realized by lengthening the focal length.