There is a pattern of Olympic rings at the bottom of the swimming pool. People standing on the shore use ordinary cameras to shoot objects at the bottom of the pool to get clear images.

Judging from your description, the camera mentioned in the title should be a leather camera. The black box part of the camera is similar to the bellows of the accordion, which can not only expand and contract, but also have a certain range of "deformation"-focusing and changing the perspective effect of imaging. (The length of the black box is the focal length f)

For example, a general camera (the optical axis is perpendicular to the "plane" where the lens and negative film are located and passes through its center) will get a trapezoidal effect when shooting a tall building at a low viewpoint, while a leather cavity camera can correct the image into a rectangle by adjusting the relative position of the lens and negative film.

As for a, b, c and d, do you still follow the convex lens imaging formula: 1/u? +? 1/v？ =? 1/f (where u is the object distance, v is the image distance, and f is the focal length), and judge the result according to this.