Abstract: An apparatus and method of mounting a lens block on an optical lens blank having predetermined optical and mechanical centers so that the lens block is centered on the blank with respect to the optical center and is provided with recesses aligned on a line through the mechanical center of the lens blank. The apparatus includes a lens blank holder, an optical center alignment device and a lens block forming apparatus having recess-forming projections. The lens blank is placed on the holder and the optical center aligned on the alignment device. The holder is then placed on the lens block forming apparatus such that the recess will be formed along a line through the mechanical center of the blank. Liquid lens block material is then introduced into the forming apparatus and allowed to harden.