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.While subjects remain in sharp focus, out-of-focus backgrounds or foregrounds are blurred smoothly and evenly with gradation that thickens toward the edges of the frame for a pleasing aesthetic effect.