Free-form is a manufacturing technology that allows cutting and polishing arbitrary surfaces
Numerically controlled generator and polisher
The surface does no longer need any symmetry
Surface defined in a sag file
Only limited by surface curvature: ~15 D
Characteristics of free-form lenses
Is free-form more precise?
- What is claimed: 0.01 D
- Very difficult to achieve in plastic
- Well tuned process with tools, soft pads and slurries not worn out, guarantees better precision than standard milling and polishing methods.
Has a free-form lens better optical quality?
- Not necessarily.
- Free-form is a manufacturing process, not a design method, neither an optical design software.
- But free-form technology will allow you to get better optics, as far as you use good optical design tools.
Why there is so much expectation around free-form lenses?
- The great thing around free-form is that ophthalmic industry is no longer tied to base-curve restrictions.
- With standard base curves, a sophisticated lens must be made with a few complex surfaces (semi-finished blanks) and spheres or torus.
- With free-form, each sophisticated lens may have its own sophisticated surface.
Why a different surface for each lens is better?
- In Optics, asphericity is the way to correct for aberrations when you cannot use many lens elements.
- In ophthalmic optics, compensation must be made by just one lens per eye.
- Each prescription, each lens position, each object position, requires a particular asphericity to get the best possible correction.
- Standard lenses uses the same asphericity for thousands of different situations: asphericity becomes useless.
- A different surface for each lens will allow a different asphericity for each lens: optimum compensation of side effects (aberrations).