The Sigma 50mm F1.4 has arrived to undoubted excitement and anticipation; as the first new, reasonably affordable fast 50mm lens for many years, it has the potential to redefine the quality obtainable in this popular class of lens through the use of modern optical design and manufacturing techniques. But it also currently commands a hefty price premium; the Sigma is considerably more expensive than any of the camera manufacturers' own 50mm F1.4 primes. So the obvious question is whether the optical quality can justify that additional outlay of your hard-earned cash; let's find out.