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

What is the difference between Optical Glass and Ordinary Glass?

Matt

Doctor, tell me about the difference between optical glass and ordinary glass.
Naze Taro

Sure. Matt, guess what are the characteristics required for camera lenses?
Matt

I guess camera lens is transparent and smooth… so, I think dust, scratches and flaws are not allowed. And, my favorate glass cup has bubbles in it but I think camera lens cannot contain bubbles, am I correct?
Naze Taro

Yes. A high degree of transparency is required for optical lens.
Matt

Wait, many glass products are transparent, too. Look at the window glass over there.
Naze Taro

Right. But when you look closer at it, the window glass contains many impurities. Optic glasses are required to travel light even with its thickness of 100 meters. Ordinary glasses with that thickness cannot transmit light because of their contained impurities.
Matt

A thickness of 100 meters? Not 100 cm, but 100 meters? That’s amazing.
How do you make high-purity glass, then?
Naze Taro

Glass is made of silica sand, quartzite, and other stones or sands from mine. Those stones or sands already look like glasses when mined. But in general, sand cannot be glass’ raw material alone. Glass is made from a mixture of sands and other materials.
Matt

Glass is made of sands! Sounds interesting.
Naze Taro

Each sand has a difference in the proportion of impurities. The higher the purity of the sand, the higher the purity of the glass. Sand that contains less impurities are expensive.
Matt

Opticical glass is made of different quality of sand from other glass.
Naze Taro

That’s right. In addition to that, as you mentioned, neither bubbles nor flaws are allowed in optical glass. Ingredients are stirred carefully to uniform component ratio in every part of the glass.
Matt

Sounds like it’s not easy to make optical glass.
Naze Taro

Let’s learn more about how optical glasses are made next time.