Process for the design of free form reflectors which accounts for manufacturing tolerances

Apparatus for designing an optical element to accommodate manufacturing errors comprising:

• means for receiving input data representing the optical power of at least one optically effective part of said optical element,
• means for calculating the optical output of said at least one optically effective part,
• means for simulating errors in the manufacture of said optically effective part by modifying said input data in accordance with expected manufacturing errors to provide modified input data representing said optically effective part after manufacture, and
• means receiving said modified input data for calculating the optical output of said optically effective part after manufacture.

An optical element manufactured by the process comprising:

• specifying a desired optical output for said element,
• providing input data representing the optical power of at least one optically effective part of said optical element to means for calculating the optical output of said at least one optically effective part of said optical element,
• determining data representing the optimum optical power of said at least one optically effective part of said optical element by comparing said optical output with said desired optical output to provide data representing the optimum optical power of said at least one optically effective part that will produce said desired optical output;
• simulating errors in the manufacture of said optically effective part by modifying said data representing the optimum optical power of said optically effective part in accordance with expected manufacturing errors to obtain modified data;
• ascertaining the modified optical output of said optically effective part defined by said modified data;
• comparing said modified optical output with said desired optical output and determining whether said modified optical output is acceptable, and
• manufacturing said optical element in accordance with said modified data.