Full Service Surfacing

Homer Optical is in an elite group of wholesale labs with in-house digital surfacing. Before we can explain what this means, let’s take a look at classic surfacing.

In the classical surfacing method currently being used in the vast majority of all labs, the process used to create a Progressive lens (PAL) starts with a molded blank with the progression on the front surface.  The blank is taped, blocked with alloy or wax, and then generated in a machine which uses milling process.The milling process creates a surface which must be refined and polished - rigid aluminum tools are used for this part of the process.  These rigid tools represent the single greatest limitation on the classical surfacing process - because they can only be used to create a spherical or cylindrical surface on the back of the lens.  Once the lens is fined and polished, the result is a finished PAL lens.

Now let’s take a look at Digital Surfacing:

In one form of digital surfacing (where the distance and progressive power is created on the back surface), the process starts out with what is essentially a semi-finished single vision blank.  Since the blank does not have the customary engravings used to identify the lens, these are added using a laser.  Once the blank is taped, these etchings are then used to block the lens.  The lens is generated in a digital surfacing generator which “turns” (vs. mills) the surface.  The milling process results in a surface which has “bumps” and surface fissures which must be fined away using a rigid tool with an applied abrasive surface.  In the turning process, the finished surface is must smoother and refined. In fact, it is similar to the surface of a classical surfaced lens that has already been fined.  All that is required to create a finished surface is a light polishing with a deformable tool (the tool must be deformable so it will not distort the progressive or distance power created by the turning).  A coating is necessary to produce a final finished surface because light scratches remain on the lens after the soft polishing.  The result is a finished progressive lens.

One caveat associated with digital surfacing is accuracy.  After all, most practitioners (or even laboratories) do not have the equipment required to verify whether the progressive design has been faithfully reproduced on the lens.  To assure accuracy, all Essilor digital surfacing lines are calibrated using a hyper-accurate auto-lensometer and a series of produced test lenses before the start of each production run.  The calibration process takes approximately 2 hours a day to complete.

In summary, Digital Surfacing is more accurate, faster, and provides a significantly better product. The primary advantage of Digital Surfacng, however, is its "flexibility."  Each individual point in a DS "shape" can be modified, or "unlocked."  This creates the potential to create an infinite number of shapes.  By contrast, real tools have "locked" points which will always produce the same shape over and over again.  This flexibility means a digital generator can produce an almost infinite number of shapes using the same cutting surface.  Also, the designer is free to change each point if she/he wants to apply customization to a progressive design.  PLUS, eliminating the rigid tools and laps are a big part of the secret because labs can now create shapes that results in aspheric and atoric surfaces – and that is what ensures the prescriptions are more accurate – down to a single micron tolerance vs. the ANSI standard of somewhere between -1.66 and -1.72 diopters of power – this gives the lens designer the ability and freedom to attempt to reduce lens aberrations even more than they were able to do with conventional lens design and lens generating techniques.