The 135mm f/2.8 Smooth Transition Focus Lens from Sony is a
manual focus prime lens that uses Sony's Smooth Trans Focus (STF)
technology for a very unique effect on defocused light sources, changing
the way defocused areas appear depending on how it is adjusted. The
lens is constructed of 8 elements in 6 groups which all help to deliver
sharp, clear photos. It has a minimum focusing distance of 2.9' and a
front-end filter diameter of 72mm.The advanced SAL-135F28 STF (Smooth Transition Focus) telephoto lens incorporates an apodization optical element that distributes light rays to create smooth, aesthetically pleasing out-of-focus backgrounds and foregrounds that make sharp-focus subjects stand out more vividly. Mounted on your Sony A (alpha) DSLR camera, this lens provides a 200mm focal length (35mm equivalent).