High Index Lenses
Previously, the only materials available to use for lenses were glass and a hard resin called CR-39. But recently, high index lenses have become available. High index materials are named because they have a higher index of light refraction. Basically, they can do the same job that glass or CR-39 does, but high index lenses are thinner and lighter. With high index lenses, you can avoid having "soda bottle" lenses.