1. A camera system, comprising: an imaging optical system that has an aperture, and focuses the light from a subject; an imaging unit for converting the light from said imaging optical system into an electrical signal to obtain an image taken; an image display unit that comprises a display region including a first display region and a second display region, and displays an image taken that is obtained at said imaging unit on said display region; and an aperture setting unit that adjusts said aperture and sets the aperture value of said imaging optical system; wherein, said image display unit displays a first image taken that is obtained by said imaging unit on said first display region in the case that said aperture value is set to be a first aperture value by said aperture setting unit, and displays a second image taken that is obtained by said imaging unit on said second display region in the case that said aperture value is set in a second aperture value by said aperture setting unit, and by doing so, displays both said first image taken and said second image taken on said display region.