Are glass spectacles with hot coatings effectively unavailable?

Discussion in 'Glasses' started by Salmon Egg, Mar 24, 2008.

  1. Salmon Egg

    Salmon Egg Guest

    I just ordered a new pair of glasses. I would have preferred glass
    lenses with hot deposited (really hard and tough) AR coatings but
    settled for plastic. The optician called around a bit and said that his
    few sources are even fewer now. I settled for plastic.

    Salmon Egg, Mar 24, 2008
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  2. Salmon Egg

    SQ Guest

    Are glass lenses heavier than plastic? If so, that might explain why
    plastic is so popular.
    SQ, Apr 17, 2008
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  3. Salmon Egg

    Salmon Egg Guest

    Glass usually is denser than plastic although the difference in weight
    is often exaggerated. As a rule of thumb, high density glass has higher
    refractive index than low density glass. This leads to thinner lenses.

    One time when I was more involved with selecting glass, many of the
    higher density glass lenses could weigh less than the equivalent in low
    index. This is especially true of large diameter lenses for myopia.
    Negative lenses are thicker at the edge. If you neglect the thickness of
    the lens in the center, the weight will go up approximately as the
    fourth power of the diameter.

    In my case, I have had cataract surgery on both eyes. The implants
    reduced the (negative) power required from external lenses. Thus, The
    weight of my spectacle lenses are muchlower than what they would be
    without surgery.

    Salmon Egg, Apr 18, 2008
  4. Salmon Egg

    The Real Bev Guest

    Considerably. They used to be cheaper than plastic, too. Hard to find
    and expensive now.
    The Real Bev, Apr 18, 2008
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