By Michael DiSanto, ABOM
Photograph by Ned Matura
Things Will Never
Look the Same Again
Major electronic retailers all over the world are announcing they are discontinuing the sale of analog televisions in favor of high-definition televisions. Another page in history has been turned. Old technology will once again yield to new technology. People will always strive to replace that which exists with something better. In the case of television “high definition” is that something better.
When it comes to reproducing the very best in clear, precise video nothing beats high-definition television. High-definition is better because it captures the smallest details of an image in order to present a truly lifelike picture. The concept we enjoy to watch on our TV has now come to the concept we use on our face to watch our TV. High-definition performance lenses are the new “something better” state-of-the-visual-art.
Digital surfacing technology, which is also known as free-form surfacing technology (the words are interchangeable but the process is the same), has broken from the limitations of traditional lens surfacing to establish a new level of excellence in lens production. Previous lenses were limited in design scope by the industries inability to reproduce the more complex surfaces necessary to address the full spectrum of the wearer’s visual needs. Traditional lens production hit the wall and stopped short when addressing key issues that diminished performance in spectacle lenses. Designers knew what they had to do to improve optical lens performance, but they were unable to translate intricate design concepts needed to accomplish improvement from the drawing board into a real lens. The industry had reached a plateau from which there was no escape until better technology could enable them to implement advanced designs. That technology is here now and it can be applied to everything from simple single vision to highly complex progressive lens designs. As with all new technology the start up cost for manufacturers is high. In an attempt to recoup their investment sooner the emphasis of the technology will be directed first at higher-end products, like progressives then, after equipment is in place, single-vision application will be added to keep capacity at its highest level.
It is important to note that digital surfacing is a process, not a design. It is the tool lens designers use to bring their optical blueprints to life. As such, all digital lenses are not created equally. A great lens must still start with a great design. Digital is simply the chisel used to create the sculpture, not the sculpture itself. Imagine 10 blocks of marble, 10 chisels and 10 different people to do the work. Of course, there will be 10 results. Some may be called art, but some may only be called a pile of gravel.
Digital: The Technology
That Frees the Design
This new approach to lens production improves the process in two key areas:
- Direct generator-to-mold precision grinding of complex designs eliminates the use of basic slumped molds that are incapable of addressing higher order lens aberrations.
- Direct generator-to-lens surface grinding that is capable of intricate, personalized and advanced aspheric corrections that far exceed the capability of lenses surfaced with classic methods.
Limitations of the Past
The primary tools in addressing the aberrations that affect human vision were the use of a corrected base curve and some limited use of aspheric surfaces.
Proper use of base curves put certain ranges of prescriptions on specific front curvatures with the idea of controlling the steepness of the ocular surface. If the ocular curve was no flatter than four diopters or steeper than seven diopters the prescription was “corrected” by moving most of the troublesome aberrations out of the center to the periphery of the lens. While not a perfect solution this method opened a comfortable viewing zone in the primary, central area of the lens.
Manufacturers were eventually able to introduce lens blanks that were uniformly aspheric on the front side of the lens. Even though this asphericity was not perfectly matched to the cylindrical powers of most prescriptions this technique served to widen existing viewing fields.
The use of corrected base curves along with manufacturer front side aspherics marked the highest extent that traditional processing could do the job. More was needed to address limitations in aberration control and contrast enhancement, but the technology of lens processing had reached its upper limit. A new process was needed in order to break the traditional boundaries of lens processing.
Leads the Way
Digital surfacing is the evolution our industry needed. Though still in its infancy, this new approach to lens surfacing will revolutionize lens processing. With it, lenses will achieve a higher level of performance and the traditional methods of lens production will be relegated to the history books.
The new technology will break the designer’s bonds by making it possible to actually produce working lenses, which in the past could only be imagined.
Innovations in Design
Made Possible With
the New Process
The future now seems limitless, and the evolution will continue, but here are a few of the major advancements digital surfacing can make possible. (Again keep in mind that the lenses ability to achieve these benefits depends on the design. All lenses that use the digital process are not equal and will not deliver benefits universally.)
- It is no longer necessary to start each job from a predetermined front side mold, but in practice molding will continue to be used as it enables manufacturers to provide a high level of production. The major step forward is that digital surfacing can now produce those molds by directly surfacing them. This eliminates the need for “slumped molds,” which while state-of-the art in the past, could only reproduce simple designs that lacked the ability to correct for higher-level aberrations like coma. By grinding a digitally direct mold the scope of the ground surface can now address a wider range of correction with greater accuracy and a higher level of consistent reproducibility.
- Digital surfacing allows certain designs to introduce coma control into the surface of a lens. When this happens, the contrast sensitivity of that wearer can be improved. Since contrast sensitivity is a critical part of human vision this innovation paves the way to a much higher performance in spectacle lenses.
- With digital surfacing the manufacturer has the ability to calculate and grind each surface directly so that lenses are personalized to the wearer’s particular needs. Because we no longer have to begin with a cookie cutter choice from a limited number of blanks predetermined by bases and adds, each lens can be tailored to maximize the performance for each unique prescription.
- New calculation engines evaluate in both type and intensity the aberrations that will result from combining a unique prescription with a particular lens design. After viewing the resulting trouble spots the digital surfacing process can correct for these errors and restore the resulting lens to the parameters of the original intended design.
- Progressive lenses have always struggled to limit unwanted cylinder. In addition to its intensity the cylinders bordering on either side of the corridor have opposing axis’ resulting in swim. Now this problem can be corrected by to aligning the opposing axis’ so that they are equalized and vertical. This eliminates swim and delivers a perception of wider useable intermediate and reading areas.
Looking at the world through digitally surfaced lenses can now be as clear as watching your favorite team in high definition. (If you’re like me, you’ll see that the green stuff they are playing on is actually grass, not carpet.)
Digital surfacing technology will continue to move ahead, but for now it is safe to say that the revolution has begun and the lenses of the future are available right now.
Michael DiSanto is an independent industry trainer based in Cleveland.