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Dr. Nazetaro’s Lesson ”Basics of Optical Glass”

How to make Aspheric Lenses

  • Matt
    Doctor, so why aspheric lenses had not been released for a long time?
  • Naze Taro
    Well, there was a disadvantage of creating aspheric lenses.
  • Matt
    What is it?
  • Naze Taro
    Do you remember that aspheric lens has complex surface curvature?
  • Matt
    Yes, I do.
  • Naze Taro
    Spheric surfaces, which has relatively simple curvature, had been made by polishing optical glass block.
  • Matt
    Really? Made by polishing?
  • Naze Taro
    Yes, with the high level of polishing skill that had developled in manufacturing spheric lenses, it was very hard to polish the complex surface curvature of aspherical lenses.
  • Matt
    So how did you make aspheric lenses?
  • Naze Taro
    The other method is pressing glass into shape with molds.
  • Matt
    Press with molds?
  • Naze Taro
    Yes. Prepare a mold die for shaping aspheric lens. Set a preformed glass, which shape is close to the final product, in the mold die, heat them together and when the glass gets soft, press them in a crucible. During the molding process, the preform is shaped into its final geometry. Then, cool the glass, that’s how aspheric lenses are made.
  • Matt
    Set preformed glass into mold. That seems easy to me.
  • Naze Taro
    Well, actually it is not that easy. As I explained in the 4th lesson, glass is melt in a very high temperature. Mold die needs to withstand the heat, but the heat resistant materials used for mold die are very expensive.
  • Matt
    I see. But I guess you can use the mold die over and over, right?
  • Naze Taro
    Yes, but mold die can be damaged easily because of repetition of heating and cooling. In addition, since mold die is made of very rigid material, it’s hard to manufacture mold die.
  • Matt
    Umm, that’s why aspheric lenses had not been popular for a long time.
  • Naze Taro
    That’s right. Since it was not easy to manufacture aspheric lenses, they had been expensive, and not capable of mass production. But because these restrictions were overcome, aspheric lenses became popular. Let’s learn about it next time.
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