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Glass
Lenses |
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There are two types of glass referred to in optics,
which are crown glass and Flint glass. Crown glass is the clearer of the two and is most commonly used. However, glass in general is the clearest material of all the mediums.
The index of crown glass is generally between 1.50 to
1.60. Where flint glass is the denser of the two ranging
between 1.57 to 1.75. In multi-focal lenses (bifocal & trifocal) both crown and flint maybe used because of the different refraction scale.
The most common composition of a glass multifocal lens
includes having a segment usually made of flint glass to be completely immersed within the other
glass, usually crown glass, giving a seamless surface
and two different prescription ranges. Crown glass is the clearest material with an Abbe Value of 59. Theoretically speaking, the higher the index of refraction the lower the Abbe Value will be. |
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Another attractive
characteristic of glass lenses is the scratch resistance
and durability factor. Glass lenses are the most
resistant to scratching of all the spectacle lens
mediums. However, it is important to note that no
spectacle lens material is scratch proof. Glass is also
the most durable to strong solvents and aggressive
solutions like acetone, paint thinner, etc. The biggest
counter to the durability and clarity of glass is the
weight of glass. Glass is the heaviest of all the
spectacle lens materials by far and must be chemically
or heat treated to pass FDA impact resistance standards.
It is important to note that coatings for plastic and
polymer lenses are getting more and more durable with
technology. |
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Pros and Cons of a
glass lens |
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Pros: |
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Cons: |
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Clearest material on Abbe
Value between 39 to 59 |
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At its natural state it is
thicker than poly and other high index lenses. |
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Most scratch resistant material |
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Heaviest material |
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Works very well with anti
reflective Coating |
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May chip or Break |
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All images and
literature above are Copy written by Solis Inc. Any use
with out the written consent
of Solis Inc. is strictly prohibited. |
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All literature on
this website is strictly for reference. Specifications
for individual needs may vary. Please consult with a
doctor or licensed Optician to accommodate individual
needs. |
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