Augmented reality system eye relief adjustment mechanism

A head mounted display (HMD) may comprise an adjustable crown band, a crown band circumference adjusting mechanism coupled to the adjustable crown band and configured to adjust a crown band circumference to releasably secure the crown band to the user's crown, an armature including left and right arms, each of the left and right arms mounted at a respective proximal end to corresponding left and right HMD attachment structures, a display mounted at left and right sides to respective distal ends of the left and right arms, and an eye relief distance adjustment mechanism configured to move the left and right arms in a timed manner toward and away from the crown band along a substantially linear path, to thereby adjust an eye relief distance from the display to an eye of a the user when the crown band is fitted on the crown of the user.