Why the Bubbles in the Lens Glass?
Modern glass making has changed a lot in modern times. It wasn’t so long ago that the bubbles in the glass were a sign the lens was of the highest possible quality. How quickly we have gotten used to photographic lenses that do not have bubbles in them. When optical glass is made all of the ingredients are mixed in a container that can take high temperatures called a crucible. The ingredients are melted at very high temperature. Even when it is melted, glass is very viscous and thick. When the melted ingredients are stirred to mix them together, the mix tends to pick up air which forms bubbles and the ingredients used in the older optical glasses tended to generate gasses as they melted. The bubbles are removed from the glass by allowing the crucible to sit in the high temperature furnace while the bubbles rise to the surface of the melted glass. Up until about 25 years ago the materials of which crucibles for optical glass making were made could not withstand the effects of the extrem
