Sony produces cameras with two lens mount systems: A-mount and E-mount. A-mount is standard on Sony unique Translucent Mirror type camera bodies, while E-mount is used on mirrorless bodies.
A-mount and E-mount features
A-mount cameras with Sony Translucent Mirror Technology offer the advantages of full-time phase-detection autofocus. The short flange back distance of mirrorless E-mount models makes it possible to design compact, high-performance bodies and lenses that offer outstanding handling and mobility.
 Lens mount  Flange back distance  Translucent Mirror  Image sensor plane
 Lens mount  Flange back distance  Image sensor plane
Full-frame and APS-C formats
Both A and E mount cameras have full frame and APS-C sensors options. Among the many sensor sizes in common use, full-frame is considered to be a large format while APS-C is a medium format. Both are popular for their individual advantages.
Sony offers full-frame and APS-C lenses with image circles that cover the corresponding sensor formats. Although lenses are usually chosen to match the sensor format, different combinations can be used to vary the crop area and angle of view when wider coverage or extra telephoto reach is desired.