Centering method for optical elements

A method for centering a circular optical element in a rotary, non-self-centering chuck, comprising:

• providing an optical element chuck, said chuck adapted to grip said optical element with at least two levels of grip;
• rotating said optical element in said chuck while making measurements of the lateral position of the outer rim of said optical element with a distance measurement probe;
• determining the positions of maximum and minimum run-out of said outer rim of said optical element as a function of the angular position of said optical element;
• stopping said chuck rotation at an angular position such that the maximum rim run-out is positioned at a predetermined point;
• reducing the gripping power of said chuck such that said optical element is still held but can be moved in said chuck in a lateral direction without damaging its surface;
• and
• moving said optical element in a direction connecting said predetermined point of maximum run-out and the axis of rotation of said chuck, in order to reduce said run-out of said optical element.