TheSmooth Trans Focus (STF) technology inphotographic lenses uses anapodization filter to realize notably smoothbokeh with rounded out-of-focus highlights in both the foreground and background. This is accomplished by utilizing a concave neutral-gray tinted lens element next to the aperture blades as apodization filter, a technology originally invented (and patented) byMinolta in the 1980s, and first implemented in a commercially available lens in 1999. In contrast tosoft focus lenses, STF lenses render a perfectly sharp image in the focus plane.

Lenses featuringSmooth Trans Focus technology:

• Minolta STF 135mm F2.8 [T4.5] (introduced 1999)
• Sony α STF 135mm F2.8 [T4.5] (SAL-135F28) (introduced 2006)
• Sony FE 100mm F2.8 STF GM OSS (SEL-100F28GM) (introduced 2017)^[1]

• STF function (an emulation of the effect in theMinolta Maxxum 7)
• Fujinon XF 56mm F1.2 R APD (a similar lens introduced byFujifilm in 2014)
• Venus OpticsLaowa 105mm f/2 Smooth Trans Focus (a similar lens introduced by Venus Optics in 2016)
• f-stop
• T-stop

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