Why Sony's A7 V Has a Third-Party Lens Problem

If you're running third-party E-mount glass on a new A7 V, that compatibility isn't guaranteed — and here's the structural reason why: Sony protects its autofocus protocols as trade secrets rather than patents, so lens makers never get the full picture when Sony updates the communication spec. Every other major mount maker files hundreds of AF patents, which at least puts the protocol details on public record. Sony files almost none, meaning sigma and Tamron are essentially reverse-engineering a moving target. Worth knowing before you invest in adapted or third-party glass for your A7 V kit.