The invention provides a newly designed head mounted virtual image display that is dramatically less in weight than is known in the art by virtue of a unique beam folding design, making possible wearable computer systems of significantly greater convenience and acceptability to a wide range of users. The unit may be used comfortably in conjunction with eyeglasses. Optical systems according to the invention are provided that are advantageous for use with emissive, transmissive and reflective microdisplays, and which provide high optical performance, compact design and clear see-through properties. Also, the invention provides an improved method of illumination for reflection liquid crystal microdisplays. This makes possible optical systems for virtual image displays of improved field of view, compactness, and shorter image path combined with good efficiency.