Smith Optics have got around the problem of how to swap lenses on a frameless design with their clever Pivlock V90 model. To change tints, simply rotate the earpieces 45 degrees, pull them off and then transfer them and the nosepiece to your preferred lens.
It's as simple and fast as it sounds, it doesn't require you to touch any lens surfaces, and thus far it's survived nine months of regular changing without developing any slop in the joint.
Lens swapping aside, the Pivlock V90 is an excellent pair of sunglasses in its own right. The tapering thickness, one-piece shield-type lens shows only minimal distortion (unlike many bargain makes and models out there), the field of view is broad and expansive with no frame to obscure your vision, and the three-point fit with hydrophilic nose- and earpieces is comfortable and secure.
It's also very light at just 25g, the rim-free design has good airflow to prevent fogging and your eyes are well protected from wind even at high speed. The moderate 13cm lens width (not including earpieces) makes for a good fit on small- to medium-sized faces, too.
In addition to a semi-rigid case and soft carrying bag, you also get three lenses included in the US$139 asking price (UK RRP TBC), including Smith's superb rose-coloured Ignitor tint – long one of our favourites for its uncanny ability to cut down the harshness of full sunlight while also remaining useful in dimmer conditions, all while simultaneously increasing contrast and improving colour definition.
Downsides are pretty minor. Unlike some of its competition, the Pivlock V90's temples and nosepiece aren't adjustable and nor is there an alternate-fit nosepiece to better accommodate different face shapes. To be fair though, the stock shape fits most faces. Also, the hydrophilic lens coating that's intended to shrug off sweat and debris doesn't work quite as well as we'd hoped but it's still more effective than no coating at all.