  Most conventional camera calibration algorithms assume that the imaging
device has a Single Viewpoint (SVP). This is not necessarily true for special
imaging device such as fisheye lenses. As a consequence, the intrinsic camera
calibration result is not always reliable. In this paper, we propose a new
formation model that tends to relax this assumption so that a Non-Single
Viewpoint (NSVP) system is corrected to always maintain a SVP, by taking into
account the variation of the Entrance Pupil (EP) using thin lens modeling. In
addition, we present a calibration procedure for the image formation to
estimate these EP parameters using non linear optimization procedure with
bundle adjustment. From experiments, we are able to obtain slightly better
re-projection error than traditional methods, and the camera parameters are
better estimated. The proposed calibration procedure is simple and can easily
be integrated to any other thin lens image formation model.
