9. Progressiv R, the "refraction-correct" progressive lens
In patent US 4 315 673 Günther Guilino and Rudolf Barth represent a progressive surface in a curvilinear cylinder coordinate system by a Fourier series of degree one. The obtained surfaces are called surfaces with variable periodicity. The main meridian is an umbilic with stabilized power zones, the periodicity k(z) of the orthogonal section changes as a function of the intersection point with the principal meridian. Based on the formulas and the figures of the patent for the auxiliary coordinate system and the variable periodicity, the design examples of the patent are reconstructed. These designs are different from the design plots published for the marketed Progressif R product. The parameters of the formulas for the main meridian and orthogonal sections are modified to obtain the market product. Progressif R is characterized by an excellent far vision quality, a relatively broad near vision part and a maximum of the peripheral astigmatism little above the add power. The reasons for the choice of the auxiliary curvilinear cylinder cordinate system and the variable periodicity are discussed.
9.1 The coordinate system
9.2 Description of the progressive surface
9.3 The patent
9.4 Progressiv R, the commercial product
9.5 The structure of the progressive surface with variable periodicity