Originally produced by Minolta
, and currently produced by Sony
, the STF 135mm f/2.8 *
, is a photographic lens
compatible with cameras using the Minolta AF
and Sony α lens mounts
. STF stands for Smooth Transition Focus
, in reference to its aperture system, which is intended to smooth the transition between the plane of focus and out-of-focus areas in the image.
The STF is a manual focus
-only lens, due to use of an apodization
filter that provides the high-quality bokeh
effect. This filter is incompatible with the autofocus
system used in Minolta and Sony SLRs, and so this lens is the only Minolta/Sony A-mount lens produced without autofocus capability. It is also the sole such lens having a manual aperture ring.
The apodization filter is a neutral gray tinted lens element, placed so it affects the light distribution of the circle of confusion
.Apodization (cutting off the feet!) is a process in spatial signal processing which can enhance resolution by reducing the secondary maxima in the diffraction pattern of the lens aperture. In this lens it is also deemed to improve the "bokeh" of the lens,that is the character of the image in the out of focus areas.
in this lens refers to the effective aperture opening and determines the depth-of-field produced by its use. The T-number
refers to the amount of light which passes through the lens and is collected on the film or sensor in relation to a lens without an apodization element.
The lens, unusually, offers two... Read More