The Attack MTB ChromaPop Sunglasses from Smith are some trail-ready shades that use photochromic technology to automatically adjust the tint from clear to grey depending on light conditions. It's Smith's most versatile lens and it shifts to allow anywhere from 20 to 85 percent of visible light transmission to enter when exposed to sunlight, so you can comfortably wear your sunglasses in a variety of lighting environments from exposed slick rock trails to Pacific Northwest loam.These MTB's also ship with an extra ChromaPop low light amber lens that's super easy to sub in with Smith's MAG lens interchange system. Coverage is rated as large with a medium fit and for fog-free performance, the Attack MTB features a ventilation channel in the brow. Durable materials like the TR90 frames with auto-lock hinges ensure these sunglasses are in it for the long haul. You also get a secure fit with the two-position, hydrophilic nose pad and megol temples and the glasses come with a performance case and microfiber bag.