This is a glass photochromic copper lens base.
The G3SX is the gold standard for freshwater fishing. The copper lens colour is excellent at separating fish from rocky and sandy freshwater streams. This makes it an exceptional sight fishing lens. With a high light transmitting nature, the G3SX is also excellent in brown or muddy streams. It is suitable in all light conditions when sight fishing.
This lens is also an excellent snow and hazy condition option. The lens cuts down on haze exceptionally well, delivering a clearer image than what you would see with the naked eye. Being a deep copper, highly reflective white snow is also clearer to look at through this lens due to its ability to enhance detail in flat light.