I loved my Smith Buzzsaw shades with interchangeable lenses, but they were phased out some time ago. Enter their replacement, the Smith Factor series, which improve on the Buzzsaws with a nice frameless design.
The Factor comes in three configurations, all with the same frame but progressively larger lenses: the Factor, Factor Max and Factor D-Max. I picked up the D-Max for glacier and alpine use, figuring more is better. It’s a great system, coming standard with four lenses: clear mirror (for biology lab or birth control), yellow (for high contrast Bourne activities: think driving and shooting), RC30 (rose-copper 30% light transmission: preferred for contrast on snow) and polarized brown (for the general cool look).
All in all it’s a great value from Smith. The shades even come with a nice zippered stiffie nylon case, with removable storage for the extra lenses. The only thing they don’t include is a cleaning cloth, so pick one up to protect your investment. Check out prescription lenses too.