Until now, the market has seen the introduction of many methods for using lenses from one camera system with a body from a different system. In the digital age, however, camera systems have become much more complex, and it is challenging to create a mount converter that aligns both the mechanics and software of the lens and body. Creating a converter that matches lenses for current DSLRs to bodies for mirrorless interchangeable-lens camera systems is even more challenging. Now the market demands a converter that goes beyond simply aligning the flange back distance to retaining full functionality.
Read: Full Details (on Sigma’s website)