Calculation of the number of cameras required to capture the scene is an essential problem in a practical light field based free viewpoint video (FVV) system. Existing methods calculate the Nyquist rate by assuming a band-limited signal and perfect reconstruction of an arbitrary view using linear interpolation, which often results in an impractically high number of cameras. This paper proposes a new method based on the concept of effective sampling density (ESD). It is demonstrated that there is a trade-off between the depth information accuracy, the required number of cameras, and the desired rendering quality, which could be exploited to minimize the number of cameras for a given objective. Theoretical and numerical results show that the resulting number of cameras is significantly lower than what was reported in other studies with only a few percent reduction in the output PSNR. Moreover, it is shown that the methods proposed in those studies are special cases of the one presented in this paper.