Though Optical lens with free-form lens (FFL) can be significantly used in optical rectification, it is very difficult to manufacture it. Computer-controlled optical surfacing technology is used to fabricate it efficiently. In the stage of figuring FFL, the component is fixed with vacuum flat sucking disk, then ground by the progressive mode while the abrasion wheel is trimmed on-line. A lapping and polishing tool that conforms to the shape of FFL is used to finish the optical mirror. Because FFL has no any constraints, general interferogram technique can not be applied to its measurement and the accuracy of three-coordinate measuring machine is too low. So a high-precision measurement method based on image conversion is developed to measure the surface. Generally speaking, the precision after forming is under tens of micron. Then the error correction technology is employed to improve surface precision. Getting input controlled variables from error dot matrix involves deconvolution. Least-square filtration is used to solve deconvolution and wavelet analysis is used to filter fringe and tip. Then the surface after error correction is measured again. So a closed loop is formed. The accuracy of optical mirror in our experiment is under 4 micrometers while Ra is under 5 nm.
Free-form technology is a logical extension of Design by Prescription, pioneered by scientists at SOLA. Their free-form progressive lens design is called SOLAOne, which uses high-tech computer-aided ray tracing technology to deliver the most advanced progressive-lens technology on the market. It allows the lens manufacturers to incorporate their specific design onto a lens blank without having to compromise visual acuity, as seen with traditional progressive lens designs.
Free-form technology virtually eliminates unwanted radial astigmatic error, the most common cause of non-adaption in patients with presbyopia. Traditional progressive lenses use one base curve to cover a number of prescriptions, which will correct power errors with a specific prescription, but yields a compromise with adjacent prescriptions within a given range.
The SOLAOne design allows presbyopic patients the ability to see at various distances without residual image jump (base down prismatic effect), restrictive focal lengths, or demarcation lines. SOLAOne employs aspherical curves across the front surface of the lens (below the major reference point), while at the same time a gradual decrease in the radius of curvature is used from the distance portion to the near area. This results in a lens that has multiple centers of curvature, which allows for multiple focus points.
Exactly what is the progressive corridor? Simply put, a corridor (umbilical line), or gradual increase in plus varying conic sections (curves) from the distance portion to the near portion of a progressive lens, creates additional plus power. As the add power increases, positive radial astigmatic dioptric power (plus cylinder) is introduced in the lens. The result is skewed aberration toward the periphery of the lens.