The trend over the last couple of years has been to add a second camera to the back of high-end and – in some cases – mid-range phones. But why would you want a second camera?

We’ll explain the benefits and the differences between the various systems on offer from Apple, Huawei, LG, Motorola, Nokia and why you might not need a dual camera at all.

The zoom lens

On Apple’s ‘Plus’ models, the second camera has a telephoto lens. This lets you zoom in and get a close-up but, unlike simply cropping a standard photo, you get a lot more detail.

That’s because the lens on that second camera has a lens that’s twice the focal length of the main camera.

Should I buy a dual camera phone?

You’ll find a similar system on the OnePlus 5 and other phones, but the drawback with all of them is that the telephoto  lens has a smaller aperture than the main lens. That means it lets in less light and isn’t much use in the dark.

In fact, if you try to use it in the dark on an iPhone, you’ll actually get a photo from the main camera zoomed in digitally, so it’s not as good. Here are two photos from the iPhone 7 Plus that illustrate the difference between the two cameras:

Should I buy a dual camera phone?

Should I buy a dual camera phone?

Also, the resolution of the second camera can be lower on some phones and more often than not, the telephoto camera doesn’t offer optical stabilisation so video isn’t as smooth and photos are more likely to be blurry.

That’s not the case with the iPhone 8 Plus and X which do have OIS on the telephoto camera, but they’re the exceptions at the moment.

The telephoto lens tends to be used for portrait photos, and the main camera’s duty is to supply the depth information. This is used to work out what’s in the background so it can be artfully blurred to mimic the effect you get with a DSLR. It tends to work pretty well, too.

Overall, though, it’s a decent benefit over having just one camera.

The wide-angle lens

LG was first to pop a wide-angle lens on the G5. It was fun, but the distortion made it look as though you’d used a GoPro, such were the curved lines which should have been straight.

However, things have improved in the last couple of years and the latest phones, such as the V30, Moto X4 and Asus’ ZenFone 4, can shoot video and photos with much less distortion.

Should I buy a dual camera smartphone?

However, watch out for lower-resolution sensors for this secondary lens. For example, the Zenfone 4 has an 8Mp wide-angle camera rather than 12Mp for the main one.

Here's how the cameras on the Zenfone 4 compare, with the wide-angle below the standard view:

Should I buy a dual camera phone? Standard

Should I buy a dual camera phone? Wide-angle

The LG V30 has a 16Mp main camera and 13Mp wide-angle one, so the difference isn’t too noticeable.

The disadvantage is that we’ve yet to see a phone with this setup offering a portrait mode, so if that’s a priority for you, it’s probably best to go for one of the other types of dual camera.

The colour + monochrome combo

Huawei first put two cameras on the back of a phone with the P9, teaming up with Leica to do so. Recently Nokia has adopted a similar system for the Nokia 8.

It’s the only dual setup which uses two identical lenses: the main difference is that the second camera has no colour filter and can therefore only record in monochrome.

The Mate 10 Pro - below - has this setup with a 12Mp sensor for the colour camera and - unusually - a higher 20Mp resolution for the mono camera.

Should I buy a dual camera phone?

The system has a couple of advantages. First, the two cameras allow depth information to be discerned, which allows you to get faux bokeh which makes for great portrait shots. Here's an example:

Should I buy a dual camera phone?

Second, and much less of a tangible benefit, is that the monochrome camera can capture more light which in theory means slightly more detailed black-and-white photos with less noise. In practice, though, it’s hard to see these improvements and you’ve got to love taking mono photos.

The disadvantage is that you can't take wide-angle photos, or get the optical zoom of a telephoto lens.

The single camera (aka Google Pixel)

You don’t need two cameras to get blurry backgrounds. Google’s Pixel phones (both generations) have offered this feature and with the Pixel 2, you don’t even need to raise the camera after taking a photo to grab the depth information.

Should I buy a dual camera phone?

Essentially Google uses its vast ‘computational photography’ processing power to analyse a photo and figure out what’s the subject and what’s not.

Obviously you don’t get the benefit of a wide-angle or telephoto lens, but again, Google reckons with better image processing, the Pixel 2 shoots great telephoto shots which match or beat the iPhone in certain circumstances.

Check out our in-depth comparison of the best phone cameras.