Technical Lenses
Q. Can we tint plastic photochromics ?
A. Generally plastic photochromics are adversely affected by the heat of the tint bath, we have however managed to get up to 75% LTF into Sunsensor material. Please also see NXT photochromics available in Copper 40% - 12% LTF and Amber 77% - 18% LTF.
Q. What indices can be slabbed off in plastic material ?
A. 1.5 - 1.67 index.
Q. What is the highest index currently available with a sunglass tint ?
A. We can supply up to 1.74 index with a tint from Seiko; here in the UK 1.67 is the highest material.
Q. What options have I for a high add in a bifocal in mid or high index?
A. Options to include 1.6 CU28 Adds to 4.50 (O L C page 57) CHU8 1.67 C28 Adds to 4.50 (O.L.C page 69) lens code CHU8
Q. What options do I have for -20.00 and over in any index or material?
A. Options include Super-lenti 1.8 index up to -48 lens code WSL8 and in Glass (OLC pages 92).
Also 70mm Lentic 1.7 index up to -33.5 Glass 30mm bowl lens code HL30 (O L C page 90). Also custom made lenti colours in either CR39 or glass are available.
Q. What are my options for prism control in the vertical meridian?
A. Options include slabbing off prism imbalance in the reading portion of a bifocal, available in CR39 D28, CR39 D28 Transitions, Resin 1.60 D28, Norville can custom slab off from 1.5D to 6.0D of imbalance. Other options include Franklin Split where four separate lenses are made incorporating the Prism requirement, cut in half and then distance and reading are bonded together.
Q.What are my options for prism controls in the horizontal meridian?
A. Options include Glass round 30 prism control 1.5 Index (OLC page 84) lens code 30PC and code 30PC PE 1.5 index photogrey extra (OLC page 84). Or of course a Franklin Split in CR39.
Q. What are my options for upside down bi-focals?
A. Options include Glass round 38 upside down bi-focal (OLC page 84) lens code GRUP. Norville can of course custom make most bi-focals turning them around on their axis so the bi-focal can be placed at the top during glazing.
Q.What are my options for high cylinders and prisms?
A. Generally most mid and high resins can be used for this purpose particularly thick blanks are available in 1.60 and 1.67 resin material which allows us to get up to 20.00D for either cyl or prism in single vision. We would suggest that this is reduced to a maximum of 15.00D for bi-focals in these indices.
Q. What does the phrase integral coating process” mean?
The overall coating system on a plastic ophthalmic lens, of course, has three components, each performing its own function:
1) The hard coating, directly on the substrate (often with an intermediate coating to improve adhesion), which is intended to impart the desired surface hardness to the product.
2) The anti-reflection coatings to enhance transmission. These also produce the characteristic reflection colours. They are applied on top of the hard coating.
3) The protective coating, a hydrophobic material that repels water and dirt and blocks air from the lens.
“Integral coating process” is the new term for a process in which these three components are applied in a single production step. Such processes are nothing new in the treatment of ophthalmic lenses; they have been on the market for years and most of them deliver very high quality.
Q. What advantages does a hydrophobic or “clean” coating offer?
A. As the outermost layer and hence the one in closest contact with the air, such a coating acts to reduce friction and to keep water and dirt from the surface. The word “hydrophobic” indeed means water-repelling. Hydrophobic coatings are widely used today in all aspects of lens coating.
Q. Can I get a bifocal in Ultra high index 1.74?
A. Yes available in C 28 from Norville. (OLC page 79)
Q. Can I get a high index bifocal in Transitions?
A. Yes, available in AtLast in both Polycarbonate 1.59 and Resin 1.67 Brown and Grey. (see our lens information pages)
Q. Can Norville glaze 8 base wrap frames which are semi-rimless?
A.Yes, Norville have recently installed the new Mei 641 - 5 axis edging equipment here in Gloucester. The Mei copes with all specialist wrap and rimless frame designs using either Trivex,NXT or Polycarbonate lens materials for the best finished results |
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