6. Varilux 1, the first commercial progressive lens
The key of success of the Varilux project was to link the mathematical research on progressive surfaces inseparably to the engineering of the manufacturing process. Different manufacturing methods using circles and conic sections as generating surfaces are discussed (patents US 2 869 422, US 2 915 856) . In order to get rid of the constraints of the production process based on especially shaped cams, the "point by point" manufacturing had been developped (patents US 2 982 058, US 3 041 789 ).
The calculated Varilux 1- type design in this chapter is built from an umbilical principal meridian with stabilized zones for FV and NV, together with circles as orthogonal sections. The equation for the meridian is obtained by numerical integration of its curvature. Several possibilities for a stabilized meridian are considered. The progression length is rather short with 14mm. The obtained surface is distinguished by large, clear far- and near- vision zones corresponding to the target, a progressive with optical characteristics close to a bifocal lens. In the periphery of the progression and near vision zones the design shows a rather high amount of aberrations (astigmatism and distortion).
6.1 Focus on the manufacturing process
6.2 The coordinate system
6.3 The principal meridian
6.4 Geometry and equations of the progressive surface
6.5 Analysis of design and calculations