Explainer: why your smartphone now comes with a dual lens

Cameras in smartphones are getting better every year, especially given the increasing power of the portable computers they're attached to, but they're limited by the physical size of the phones they're in. 

Some of the tricks phone manufacturers have employed to overcome this limitation — which has generally meant a limited sensor size a fixed lens with a fixed focal length and no optical zoom — have been successful (including software solutions like high dynamic range), while others have failed (like the zoom lens attachments made by Samsung, Sony, LG and Motorola).

The Huawei P9's dual 12MP setup. 

The latest trick is employing multiple lenses.

HTC were first to debut a dual lens camera back in 2014's One M8. The main lens was a traditional 4MP shooter, with a second lens that captured only the depth information of the scene. The information provided by the depth sensor was used to separate a foreground subject from the background, allowing you to refocus or recolour either part of the image.

iPhone 7 Plus (and iPhone 8 Plus) features one standard wide-angle lens and one telephoto. Photo: Bloomberg

The results were hit and miss. The image separation worked in only the best conditions, with a well lit subject and and a dead still arm, and the added depth to images couldn't paper over the M8 camera's other noticeable flaws.

The first dual lens system that really caught the market's attention came as part of Huawei's P9. Here, Huawei use a monochrome lens to quickly capture an image with as much detail as possible, with the second lens used to capture colour. Both cameras have different focal lengths, and the P9 included a dedicated "depth processor" that calculated depth based on the difference between the lenses. Finally, colour was matched to the black and white image. All of this happened in the time it took to click the shutter.

Apple joined the dual lens market with the iPhone 7 Plus. Apple used a similar methodology, comparing the image produced from two different focal length lenses, only here they are comparing a wide-angle to a telephoto lens. This gives the added bonus of an optional two-times optical zoom, allowing for close ups.

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The Note8 is Samsung's first foray into dual lens cameras, and like Apple it's using a telephoto and wide-angle lens to pull this off. Unlike Apple, Samsung gives users the ability to "pull focus" in real time while taking the image, or to edit after the fact.

The Note8 features optical image stabilisation on both lenses. Photo: AP

The Note8 is currently the only dual lens system with optical image stabilisation in both lenses, which allows the portrait mode to work in less forgiving conditions, handy for capturing fast moving toddlers, or portraits in low light. The iPhone X will match this feature when it ships in November, and thanks to the array of sensors powering Face ID on the iPhone X, Apple can bring portrait mode to the front-facing "selfie cam" as well.

Today, you can find similar dual lens cameras in phones from Nokia, Oppo, OnePlus and Asus. LG and Motorola are the outliers. In the LG G6 and Moto X4, the dual lens systems are two independent cameras, there's no fancy cross image calculations happening here. Instead, the two phones simply switch between a standard wide angle lens, and a super-wide angle.

Smartphone image sensors are continuing to improve, but the real breakthroughs are coming from manipulating the images coming off those tiny sensors with the processing power and software of today's flagship phones. Google's upcoming Pixel 2, for example, sticks with one camera lens but is apparently able to sense depth by comparing the minuscule difference in perspective between adjacent pixels.

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