Sony E-Mount (FE / E)
Direct Answer
The Sony E-Mount (introduced in 2010 for NEX mirrorless and expanded in 2013 to 35mm full frame as FE) is a 3-tab bayonet lens mount featuring a 18.0 mm Flange Focal Distance (FFD), a 46.1 mm throat diameter, and a 10-pin high-speed electronic interface. It is the most widely adopted open third-party full-frame mirrorless mount in the photographic industry.
Source: Sony Corporation Basic Specification Disclosure Standards / CIPA
Specs
| Flange Focal Distance (FFD) | 18.00 mm (0.709 in — distance from lens mount mating surface to sensor plane) |
| Inner Throat Diameter | 46.1 mm (1.815 in) |
| Bayonet Tabs | 3 asymmetrical locking tabs with clockwise twist lock |
| Electronic Interface | 10 gold-plated leaf contact pins (supports real-time eye-AF tracking, OSS, active lens breathing compensation) |
| Full-Frame vs APS-C | FE lenses cover 36×24 mm full frame; E lenses cover APS-C (auto-crops on full-frame bodies) |
| Third-Party Protocol License | Open disclosure to lens manufacturers (Sigma, Tamron, Zeiss, Samyang, Voigtländer) |
| Camera Systems | Sony A7 / A9 / A1 series, FX3 / FX6 cinema lines, A6000-series APS-C bodies |
Short Flange Adaptability
Because Sony E-mount's 18.0 mm FFD is significantly shorter than SLR mounts (Canon EF: $44.0\text{ mm}$, Nikon F: $46.5\text{ mm}$, M42: $45.5\text{ mm}$), passive or electronic smart adapters (such as Sigma MC-11 or Metabones) easily bridge the physical distance, allowing virtually every vintage SLR lens ever produced to achieve infinity focus on Sony mirrorless bodies.