When it comes to smartphone cameras, the only number that has mattered for the past decade is how many megapixels they have. Now an innovation is arriving that makes the smartphone calculation even simpler: does it have one camera on the back or two?

A dual-lens system can bring all sorts of advantages to a smartphone that hitherto have been the preserve of standalone cameras. It can make autofocus faster and improve low-light photography. One of the pair can add extra zoom without compromising picture quality or adding bulk. The extra camera can also allow a wider angle for better landscapes and selfies. When combined with the right image-processing software it can add effects associated with expensive single lens reflex cameras, like a bokeh background or shallow depth of field, without needing to attach extra lenses.

The next iPhone is expected to come with a dual-lens camera when it is released in September but Apple will not be the first to introduce this technology. Earlier this year, LG’s G5 phone added a wide-angle lens alongside its main camera while Huawei’s flagship, the P9, comes with a Leica-branded twin-lens system that boasts image enhancements.