A key role of the design total optical thickness in the synthesis process is demonstrated by practical examples and confirmed by rigorous theoretical results. A special development of the needle optimization procedure called the synthesis by gradual evolution is proposed. This synthesis process does not require any starting design. It automatically constructs a set of designs with various combinations of three major design parameters: merit function value, number of design layers, design total optical thickness. This provides the optical coating engineer with additional opportunities in choosing the most practical design.© (2004) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.