Light-field photography is an extension of traditional photography that enables among other effects refocusing, viewpoint change, and aperture synthesis of still images by digital post-processing. It achieves this capability by recording 4-dimensional radiance information rather than 2-dimensional integrated sensor irradiance. Consequently, optical design tools need to change in order to design these new devices. In this article, we propose an optical first-order model that abstracts the architecture of any light-field camera as an Equivalent Camera Array (ECA). This model enables a comparison between different designs and allows for a simulation of the effects of parameter modifications to a design. We present equations for optical properties such as the depth of field, the angle of view, as well as important parameters for algorithmic performance such as the triangulation baseline. We provide an experimental validation of our model by measuring the properties of a real light-field camera. We are able to extract unknown physical parameters of the system such as the focal length of the main lens.