A macro of a freshly surfaced lens, a fine spiral toolpath catching the light.

Making and checking a lens

Freeform surfacing

Optical glossaryMaking and checking a lens

Manufacturing in which a lens surface is cut point by point by a computer-guided tool from a map calculated for one order, rather than molded. On made-to-order CLIFF lenses it is the back surface — the surfacing and the design both — on every made-to-order tier. Versatile, the stock lens, is molded, not freeform.

A semi-finished blank arrives with its front already molded. The back is cut away to the prescription, leaving the finished lens inside the outline of the blank.

Illustrative · the shape of the principle, not measured data

In more depth

A freeform generator cuts a lens surface point by point with a diamond tool, following a map calculated for one order. Because the surface can take any shape the software describes, it is not limited to the fixed curves of traditional tooling — a progressive's design can be cut directly into the back of the lens.

That freedom is what allows a design to be calculated for an individual: the prescription, and in more advanced designs the frame's tilt, wrap and vertex distance, change the surface the machine cuts. After cutting, the surface is polished without losing its shape, then coated.

Related terms

Semi-finished blankA lens with a factory-molded front surface, finished by surfacing the back to the prescription. Every CLIFF Rx lens starts as one: freeform surfacing is how its back is finished.Progressive lensA lens whose power changes gradually from distance at the top to reading at the bottom, with no visible line.Vertex distanceThe gap between the back of the lens and your eye. At strong powers, a change in this distance changes the effective prescription.Pantoscopic tiltThe forward tilt of a frame relative to the face. Individualized designs account for it; standard designs assume an average.

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