Sony's first full-frame mirrorless camera, the body that launched the E-mount revolution.
The Sony A7 was launched in 2013 as the world's first full-frame mirrorless camera with an interchangeable lens mount. By putting a 24.3MP full-frame sensor in a body the size of an APS-C mirrorless camera, it proved that full-frame did not require a DSLR-sized body. It launched the full-frame mirrorless revolution.
The 24.3MP sensor delivers excellent image quality with good dynamic range. The body is remarkably compact for full-frame. However, the first-generation AF with 117 phase-detect and 25 contrast-detect points is slow and unreliable by modern standards. There is no IBIS. Battery life is poor at approximately 340 shots.
The A7 is historically significant as the camera that proved full-frame mirrorless was viable. It was followed by the A7 II with IBIS, A7 III with improved AF, and A7 IV with AI AF. Each generation dramatically improved on the original.
Very cheap used as it is three generations old. The A7 II with IBIS is a much better camera for a modest premium. The original A7 is primarily of interest at very low prices or for adapted vintage lens use where AF is not needed.