Dual Cameras in Smartphones: How Do They Work?

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Only recently, we did a feature on three of the most popular photography apps, for smartphones, available today. As manufacturers continue to push boundaries with the cameras on mobile phones, app developers are constantly working on unleashing the full potential of the hardware on offer. While both aspects of technology progress almost simultaneously, it might seem that the latest advancement in smartphone cameras is leading the development of professional-grade third-party apps.

An All-New Chapter in Mobile Phone Photography

And this time, we are, in fact, bringing our focus to the dual camera which is arguably the hottest trend in the smartphone industry right now. We have picked three smartphones each belonging to a different price range, but all having the much talked about two-lens setup – Apple iPhone 7 Plus, Honor 6X and Huawei P10.

But, each of these handsets executes the dual camera in their own way – not one matching the other in entirety.

The Myth

It must be understood that the existing dual cameras, in general, work just like conventional smartphone cameras that come with a single lens. What dual cameras offer is additional functionality with respect to the secondary lens which works alone in almost all cases.

Dual camera
Usually, barring few exceptions, other than a conventional primary lens, the secondary lens is a telephoto lens designed to click Portrait images


(Unless we are talking about smartphones like the Nokia 8 and Huawei P10 whose secondary monochrome lens (black/white) can be made to work with the colored primary lens to create an image. Note that in both these phones, the secondary lens captures images only in black & white)

Largely though, it is a misguided belief that both lenses operate together at the same time to capture a moment thereby producing a high quality image. It simply doesn’t work like that, not yet. However, the inclusion of a secondary lens has indeed given an interesting aspect to the mobile phone photography. Compared to a good dedicated digital or a DSLR camera, what a smartphone’s dual camera currently does is mostly gimmicky, but it is interesting nevertheless.

On to the Dual Cameras

Starting with the Apple iPhone 7 Plus – needless to say, it made dual cameras popular by starting a trend and has played a major role in making them mainstream. Even today, the iPhone 7 Plus remains the most popular, dual camera-equipped smartphone in the world. Whether or not it is the best is a separate matter.

The dual camera in iPhone 7 Plus is a pretty straightforward affair but it is effective. Both lenses are of 12 mega-pixels whereas the primary lens has an aperture of f1.8 while the secondary lens has an aperture of f2.8. Good things first – the secondary lens has a true 2x optical zoom (which basically means zoom through the lens itself resulting in completely lossless zoomed-in images).

(On the other hand, the ‘digital zoom’ is completely done by the software as it multiplies the pixels to make the subject appear closer, but it sacrifices quality)

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Secondly, the 7 Plus camera is primarily famous for the ‘Portrait’ mode which produces the much sought after ‘Bokeh’ effect. What is Bokeh? It is a picture in which the subject is kept closely in focus while the background is blurred or softened progressively – things that are farther than the camera (closer to the horizon) are more blurred than the ones closer to the camera. The Bokeh effect provides an image with fantastic depth-of-field.

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And here comes the not-so-good-stuff about the iPhone 7 Plus camera. While the secondary lens does its best to produce a good depth of field in the ‘Portrait’ mode, it is not a true Bokeh effect as it is completely handled by the software.

(This again brings our attention to the fact that to generate a genuine Bokeh effect or to capture a good Portrait image, it is the lens (hardware) which has to do the job. Clearly, the current smartphone cameras are not that capable as of now)

Also, the OIS (Optical Image Stabilization) incorporated into the iPhone 7 Plus camera only supports the primary lens, not the secondary one.

Coming back to the Portrait images, all modern phone cameras especially with the Phase Detection Autofocus work to isolate the subject-in-focus from its surroundings. This means that good smartphone cameras can actually generate pretty decent Portrait images without needing a dedicated secondary lens or a separate ‘Portrait’ mode for the same.

iphone 7 plus Dual camera
iPhone 7 Plus made dual cameras popular and companies are finding different ways to incorporate the technology


The second phone – Honor 6X. While the Apple iPhone 7 Plus is a high-end expensive smartphone, the Honor 6X lies at the much lower end of the price range. In India, it starts from INR 11,000 Rs for the 32 GB storage version. And yes, it comes with a dual camera – combination of a primary 12 mega-pixel lens and a 2 mega-pixel secondary lens. There is no Optical Image Stabilization.

Perhaps the only similarity in dual cameras between this and the one in the iPhone 7 Plus is the Phase Detection Autofocus and the Portrait mode (although it is not called so, the Portrait images can be clicked by enabling the ‘Wide aperture’ option).

Furthermore, the Honor 6X camera offers a number of conventional manual settings for its primary lens whereas for the secondary lens, there is an option (in the form of a horizontal slider) to set the level of blur effect (not in terms of intensity but how much area in the image can be blurred). This option can come in handy while trying to click Portrait images of objects of different sizes.

(Techno-tip: Aperture indicates the size or width of the sensor. The lesser the number, the larger the size. For example, an aperture of f1.8 is larger than an aperture size of f2.2)

In Honor 6X, the aperture can be taken up to f0.95 through the slider. Of course, it is only a simulation and not the actual hardware-driven depth-of-field effect. But it is still an interesting trick if implemented right. We would say that the 6X camera does an OK job at best.

Lastly, on to the third smartphone – Huawei P10. The dual camera in this one is rather interesting – you guessed it – the secondary lens is a monochrome which captures images only in black and white. And yes, in this phone, the monochrome lens can work simultaneously with the color lens to generate higher quality images.

The P10 camera is a combination of a 12 mega-pixel color lens and a 20 mega-pixel monochrome lens where both lenses have an aperture of f2.2. It also gets, what Huawei calls, 2x ‘lossless’ zoom which can go up to 10x digitally. The idea of having one lens as monochrome is to capture good contrast and when combined with the primary 12 MP lens, the result is a 20 MP colored image rather than a 12 MP one. In this case, the image processor is claimed to work intelligently so as to combine the high contrast from the Black & White image, with the details in the colored version of the image, eventually generating a high quality 20 MP colored image. Like the camera in Honor 6X, there is an option to adjust the aperture in order to generate a desirable Bokeh effect.

Smartphone Cameras on the Verge of Greatest Innovation So Far

We have had some extremely impressive mobile phone cameras for a number of years now. Suffice it to say that especially the major players – Apple, Samsung and Nokia – have all played remarkable roles in their own way to make cameras one of the biggest selling points for the smartphones today.

Last year, Apple brought the dual cameras into the mainstream and started the fastest growing trend in the history of the mobile phone industry. And from what we have seen so far, the innovation has only begun. We have a lot to see and we are particularly positive that we shall see some amazing stuff related to the phone cameras within the next one year or so.

Competition is at its most intense right now between the phone manufacturers – there are established players and then there are those looking to make a comeback (Nokia and Blackberry). With the AR and VR (Augmented Reality and Virtual Reality respectively) technologies slowly coming into the play, the cameras will be at the forefront in the future to showcase the technological prowess of a smartphone.

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