This is the first of two articles on the Extant Life Volumetric Imaging System (ELVIS) describing a combined digital holographic microscope (DHM) and a fluorescence light-field microscope (FLFM). The instrument is modular and robust enough for field use. Each mode uses its own illumination source and camera, but both microscopes share a common objective lens and sample viewing chamber. This allows correlative volumetric imaging in amplitude, quantitative phase, and fluorescence modes. A detailed schematic and parts list is presented, as well as links to open-source software packages for data acquisition and analysis that permits interested researchers to duplicate the design. Instrument performance is quantified using test targets and beads. In the second article on ELVIS, to be published in the next issue of Microscopy Today, analysis of data from field tests and images of microorganisms will be presented.