An optical system for a head-worn computer includes an upper optical module adapted to convert illumination into image light by illuminating a reflective display through a field lens, wherein the image light is transmitted back through the field lens, then through a partially reflective partially transmissive surface and into a lower optic module adapted to present the image light to an eye of a user wearing the head-worn computer and the upper optical module being positioned within a housing for the head-worn computer and having a height of less than 24 mm, as measured from the reflective display to the bottom edge of the rotationally curved partial mirror.