Originally produced by Minolta, and currently produced by Sony, the STF 135mm f/2.8 [T4.5] is a photographic lens compatible with cameras using the Minolta AF and Sony α A-mount. STF stands for Smooth Trans Focus, in reference to its special optical system, which is intended to smooth the transition between the plane of focus and out-of-focus areas in the image. This is accomplished by the use of an apodization filter that provides the high-quality bokeh effect. The lens is not a soft-focus lens.