A working FMOS requires both an Upper Tube and a Lower Module. Looking at the FMOS System Diagram, there is a selection of Upper Tubes (Standard or Mini), in a variety of focal lengths from 60 to 500mm. There is also a selection of Lower Modules from simple optics to coaxial illumination with internal focus and again they come in a variety of working distances from 30 to 190mm.      

The FMOS Specification Chart details the optical properties of different combinations of Upper Tubes and Lower Modules. Included are numerical aperture (N.A.), magnification at the camera sensor, depth-of-field and field-of-view. Observe that, as the working distance increases, so too does depth-of-field and field-of-view. Inversely, as the above factors increase, N.A. (resolution) and magnification decrease.  NOTE: The chart also indicates those areas where a Coaxial Illuminator Lower Module will not provide a fully illuminated field.