For brevity within this text, we will also use an abbreviated CLI nomenclature when describing a design. For example, instead of referring to "the third surface in the system," we will use S3. And the "radius of curvature of the second surface of the lens" (RDY S2 in CLI) will be abbreviated as R2. Distances between two surfaces (written in CLI as THI Sk, where "k" is the number of the surface) will be referred to as Tk. And the glass of the second medium will be abbreviated as G2. Design references will be distinguished from CLI commands, which are displayed in a sans serif typeface with a shaded background.
How to Put a Lens in a Computer