Ask a simple question! Image distance! ! Image distance!

Your second question answers your first question.

@ @ Image distance (that is, the distance from the focus to the image plane) @ @

Image distance is a distance and a length, so the length can be expressed in length units and how many yuan units can be expressed.

The schematic diagram of camera imaging is the imaging diagram of convex lens, and then simplified is the imaging of small holes, as shown in the following figure (link below)