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.
Aperture Range: f/2.9-31
With a maximum aperture of f/2.8 and minimum of f/31, this lens' high speed means you can capture images in darker conditions using faster shutter speeds and lower ISO sensitivity.
Smooth Trans Focus (STF)
Smooth Trans Focus (STF) employs a special "apodization" element that controls the parts of the image that are not in focus. This does not affect the focused part of the image, only what is out of focus, and is set independently from the camera's focus and aperture via the STF ring.
Manual Focus Only
Due to the unique characteristics of the STF technology, focusing with this lens is achieved manually rather than using the camera's auto focus system.
9x Circular Aperture Blades
The circular aperture blades of this lens aid in producing smooth backgrounds. Because the aperture blades form a near circle at the wide openings used for low-light shots, spot-light sources have a pleasing circular defocused effect.