Then there are the imposters. You go to a discount shop or a flea market and see vendors offering sunglasses that look exactly the same as the high-dollar brand names for a fraction of the cost. Are you really paying that much for a name or are there fundamental differences between the look-alike sunglasses and the brand-name ones?
The biggest problem with cheap sunglasses is in the way the lenses are made. Inexpensive sunglasses have lenses made of ordinary plastic with a thin tinted coating on them. While the tint color and a similar frame design may make them look like Oakley X-Metal Romeos or Ray-Ban Predators, the actual lenses are very different. You will learn exactly how different they are, and how important the differences are, in the following sections.
Keep reading for a complete description of specific technologies like polarization, photochromic lenses, anti-reflective coatings and so on.