Optical: systems and elements – Having significant infrared or ultraviolet property – Lens – lens system or component
Reexamination Certificate
2001-08-14
2004-07-27
Chang, Audrey (Department: 2872)
Optical: systems and elements
Having significant infrared or ultraviolet property
Lens, lens system or component
C359S212100, C359S580000, C359S581000, C359S582000, C359S584000, C359S586000, C359S588000, C359S589000, C359S590000, C427S164000, C427S165000, C428S421000, C428S422000
Reexamination Certificate
active
06768581
ABSTRACT:
The present invention relates to optical articles bearing a coating which displays superior uniformity of reflection.
The optical articles according to the present invention are preferably employed in the preparation of articles such as optical lenses, including spectacle lenses, including sunglass lenses, visors, shields, glass sheets, protective screens, and the like.
Anti-reflection coatings are commonly deposited on ophthalmic and sunglass lenses in order to minimise spurious reflections, which both detract from the wearer's vision and are also cosmetically unpleasing. These coatings commonly consist of multilayer, dielectric films of thicknesses chosen so that interference effects cause destructive cancellation of reflections over most of the visible spectrum.
A coating that is not anti-reflective and that changes the reflectance of the lens can be described as a “mirror” coating. Such mirror coatings are often used in the manufacture of sunglass lenses, to produce fashionable lens colours.
When mirror and anti-reflection coatings are deposited on curved substrates (such as ophthalmic lenses), regardless of the deposition method used (e.g. evaporative, sputtered, etc.) geometrical factors result in the coating thickness being non-uniform and varying systematically over the surface of the lens. The coating thickness is typically greatest where the surface of the substrate is most normal to the incident flux of particles, and thinner where the surface faces the flux at an angle. For ophthalmic lenses, which are normally mounted with their centres facing the particle source, this means a coating that is thickest in the centre and that becomes thinner towards the edge of the lens element. This effect becomes more pronounced as the lens becomes more highly curved.
The coating thickness variations manifest themselves as visible variations in the reflectance from the coated lens. The colour (specified by “lightness”, “hue” and “chroma”) of the residual reflection changes from the centre to the edge of the lens, an effect referred to as “colour rolloff.” For lenses of normal curvature, the colour rolloff is barely noticeable and cosmetically, the lenses are considered to be acceptable. However, for very highly curved lenses, the colour rolloff is particularly noticeable and is generally considered to be unsatisfactory.
One method proposed in the prior art to reduce colour rolloff is to mount the substrate on a “planetary rotation” stage, which spins the lens about its own axis at the same time that it rotates about another central axis. The result of the complex substrate motion in the deposition chamber is that the flux of coating material is more evenly distributed over the surface of the lens, resulting in a coating that is more uniform over the substrate than would otherwise be the case. Planetary rotation is not the only option—any substrate motion at all will tend to reduce coating thickness non-uniformities. Unfortunately, implementing such substrate movement in the deposition chamber necessary involves mechanical complexity and a likely decrease in the total number of substrates that can be coated simultaneously in the apparatus, which is a severe disadvantage in a commercial production process.
It would accordingly be a significant advance in the art if ophthalmic lenses could be provided with a coating or coatings of general applicability which could reduce the phenomenon of “colour rolloff”, but without the need for “planetary rotation” apparatus.
Accordingly, it is an object of the present invention to overcome, or at least alleviate, one or more of the difficulties or deficiencies related to the prior art.
Accordingly, in a first aspect of the present invention there is provided a coated optical lens including
a lens element; and
a coating on a surface of the lens element exhibiting a substantially balanced reflectance from the centre to a radius proximate the edge of the lens element.
The lens element may preferably include a surface of high curvature, upon which the balanced reflectance coating is deposited. By the term “surface of high curvature”, we mean a surface having a base curve approximately 6 Dioptres (D) or greater, preferably 6 D to 20 D, more preferably approximately 8 D to 16 D.
The lens element may be either optically clear or tinted (light absorbing), such as a sunglass lens, ophthalmic lens element, visor or the like.
By the term “ophthalmic lens element”, as used herein, we mean all forms of individual refractive optical bodies employed in the ophthalmic arts, including, but not limited to, lenses, lens wafers and semi-finished lens blanks requiring further finishing to a particular patient's prescription.
The visual appearance of the coated optical lens in reflected light-can be quantified by measuring its reflectance spectrum in a spectrophotometer. It is well known that the reflectance of thin film coatings tends to vary with the angle of the incident light. When we speak of the reflectance from the lens we imply the reflectance of light incident at angles of 0 to approximately 30 degrees to the normal to the surface of the lens, as would typically be the case for the reflected light seen by an observer standing directly in front of a person wearing the coated lenses as spectacles. This spectral information may be reduced to three colour coordinates—a “lightness” corresponding primarily to the luminous intensity of the reflected light, and two chromatic attributes, “hue” and “chroma”, corresponding to the general colour (e.g. “red, “blue”, “green” etc.) and its vividness. (“The Measurement of Appearance”, 2
nd
ed., R. S. Hunter and R. W. Harold, Wiley, New York, 1987).
By the term “substantially balanced reflectance” we mean that where the thickness of the coating varies across the surface of the lens, the lightness, hue and chroma of the reflectance vary in a balanced manner such that variations in visual appearance are either imperceptible or generally acceptable to an observer. For example, variations in chromatic attributes, such as hue, from the centre to the edge of the lens may be balanced by a reduction in lightness from the centre to the edge.
Perceived variations in appearance may be quantified by calculating “CMC colour differences,” as developed by the Colour Measurement Committee of the Society of Dyers and Colourists. A CMC colour variation of &Dgr;E
CMC(2:1)
=1 is the limit of acceptability for textiles. Applicants have found that this is too stringent a tolerance for anti-reflection or mirror coated lenses in the ophthalmic industry. Variations between anti-reflection coated lenses of approximately 3 or less are acceptable and Applicants have observed that colour differences of up to 3-11 may exist across a lens that has an acceptably uniform appearance. Variations of up to 20 may exist in lenses that are visibly non-uniform in colour, yet that are still acceptable in appearance.
The normal incidence reflectance spectrum of a highly curved (16 dioptre) lens coated with a typical commercial anti-reflection coating is shown in FIG.
1
.
The reflectance of light of essentially normal incidence measured at the centre of the tens element is low in the visible spectrum (roughly 380-780 nm), but is significantly greater for longer wavelengths. Toward the edge of the lens element (e.g. at a radius of 20 mm from the centre), the total coating thickness may be reduced to 80% of the thickness at the centre of the lens. This is due to the curvature of the lens and the geometry of the deposition system as described above. As shown in the figure, the spectrum shifts to the left relative to the spectrum from the centre of the lens. This is a well-known phenomenon to those familiar with the art and theory of thin films. As a consequence, the higher reflectance “red tail” seen in
FIG. 1
moves further into the region of spectral sensitivity of the human eye and causes the appearance of the lens to redden toward the edges. The CMC colour difference (for CIE illuminant C) between the centre of the lens and at the radius of 20 mm
Adams Brian Douglas
Begley Paraic
Yip Brandon
Burns Doane Swecker & Mathis L.L.P.
Chang Audrey
Curtis Craig
Sola International Holdings Ltd.
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