A 24-70mm f/2.8 lens is the workhorse of choice for a huge range of photographers, but such lenses are often quite expensive. Sigma's 28-70mm f/2.8 DG DN Contemporary comes in at about half the price of competitors, making it quite appealing for those who can live without 24mm on the wide end. This great video review takes a look at the lens and the kind of performance and image quality you can expect from it in practice.