Abstract: Apparatus is provided for marking a semi-finished opthalmic lens blank for a subsequent blocking operation. The marking serves to indicate the optical center, cylindrical axis, and prism axis. The apparatus has a vertically positionable head assembly having a centered set of three holders for marking pens and an outer holder for a marking pen. An illumination head, located between the pen holders and the blank, facilitates proper orientation of the blank in preparation for marking. By way of a single activation command, such as the pressing of a button, the head assembly begins its downward descent to mark the blank and the illumination head swings aside, and both components are automatically restored to their previous, resting positions.