Specifically designed for compatibility with the Lensbaby Optic Swap system, this .42x is lighter and sharper than any other product on the market. Specs Compatible with all Lensbaby optics except Fisheye, Sweet 35 and Edge 80 Optics. Converts Lensbaby SLR lens optics from 50mm to 21mm focal length. Macro capability allows focus as close as 2.75" (7cm) from the front of the lens. Lighter, more compact, and featuring a wider angle of view than standard 0.42x wide angle accessory lenses. Measures 2" W x 1.75" H (5.1cm x 4.4cm) Weighs 2.4oz (68g) (50% less than typical 0.42x super wide angle conversion lenses) Eliminates diffusion that occurs when standard super wide angle conversion lenses are used with Lensbaby SLR lenses. Significantly reduces vignetting. Unlike standard super wide angle lenses, the Lensbaby 0.42x Super Wide Lens minimizes vignetting on crop sensor cameras. On full frame cameras, will vignette only when tilted, not when pointed straight ahead (most standard 0.42x super wide angle accessory lenses vignette on full frame cameras with the Lensbaby pointed straight ahead). In contrast with the Lensbaby 0.6x wide angle lens, the Sweet Spot of focus shrinks in size with enhanced blurring and prismatic color shifts on the edges of the photo. Attaches via 37mm screw thread onto the front of your Lensbaby optic. Front threads are 52mm to accept 52mm filters and step up rings.