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As Xperia XZ2 Premium owners will know, this is a device that takes incredible low light imagery and video. Even in extreme low light conditions, the Motion EyeTM Dual Camera captures more than the naked eye can see.

That’s thanks to its class-leading ISO 51200 sensitivity for low light photography and ISO 12800 for low light video.

But what does ISO mean and why is it so important?

A waterfront image

Quite simply, the ISO setting is a number that tells us how sensitive the camera sensor is. It stems back to the days of film when the International Standards Organisation, or ISO, came up with a standard measurement for how sensitive different films are.

Before this, different film manufacturers around the world would all different numbers for their film sensitivity, and there would be a lot of variation, producing incorrectly exposed images. The ISO standard changed that. With the advent of digital cameras, the ISO standard remained and it is now used to measure the change in the sensors’ sensitivity.

The higher the ISO value, the greater the sensitivity of the cameras sensor – so a sensitivity of ISO 6400 is more sensitive than ISO 100.

A city skate park by night

The more sensitive the sensor is, the less light is needed to create a good image.

If you are shooting a cityscape at night, or taking images in a softly lit restaurant, you may need to use ISO 1,600, 3,200, 6,400, or even 12,800.  So you can see why the Xperia XZ2 Premium’s super high ISO makes it such a formidable device – and since the camera adjusts to its surroundings automatically you don’t need to worry about settings before you shoot.

If you took an image in dark conditions using ISO 100 you would get a very dark image as the sensor wouldn’t have been set with a high enough sensitivity to record the low levels of light, or you would get a blurred image, as to get more light the shutter would have been open for long time. Having a camera that has the ability to shoot at high sensitivities means that you will be able to capture all of those unforgettable memories that can happen at night, from the beautiful city lights on a weekend away to a friend’s birthday celebrations.

A rickety pier stretches into the river

It’s always worth checking the maximum ISO value of a smartphone camera as the higher the value, the better the chance of capturing that moment, whatever the lighting conditions may be.

To get the full lowdown on how Sony managed to pack so much amazing technology into the XZ2 Premium’s Dual Camera, we spoke to Kensuke Mashita, Head of Camera Technology Marketing, and Shuichi Goto, Senior Camera Engineer.

Shuichi Goto and Kensuke Mashita
Shuichi Goto and Kensuke Mashita

What is the Xperia XZ2 Premium’s Motion Eye Dual Camera and what are its new features?
It’s our most advanced camera to date. It’s equipped with an even lower lens aperture than our normal Motion Eye camera, and it’s supported by a secondary black and white camera sensor.

It also includes an in-house developed ISP chipset, AubeTM, that can “fuse” images from both sensors in real time, resulting in impressive ultra low light photography and videography.

In low light the XZ2 Premium camera combines the images from both sensors and blends them together. The monochrome sensor’s low lens aperture combined with a large pixel pitch enables it to record more details in low light than a normal colour sensor.

What is the ‘Fusion Image Signal Processor’ technology?
The Fusion technology is one of the unique core technologies in Sony’s Xperia XZ2 Premium. We combine the highly sensitive monochrome luminance signal with the RGB colour signal to get up to four times better low light sensitivity than a conventional smartphone. The AUBE chipset is what makes this possible in real-time, even when filming in ultra low light.

How have you managed to prevent the image noise that usually comes along with high ISO values?
Higher ISO settings cause more noise on both photos and in videos. To reduce noise, various suppression methods have to be applied. However, suppressing noise also reduces image quality and causes loss of detail.

Our Motion Eye Dual Camera is equipped with both a colour sensor and a black and white sensor. The Black and White sensor has no colour filter that blocks light from reaching the sensor. It is also designed with a higher pixel pitch and lower aperture lens.

A cafe sign is illuminated against the night sky

These features together enable the sensor to achieve very good low light performance with low noise. On top of this, we also applied some noise suppressing algorithms to make the final result as clean and detailed as possible.

A city bridge in lowlight

Who else at Sony worked on this project?
Inside Sony group we have several imaging technology departments. During the development, the Sony Mobile camera team collaborated closely with professional engineers in each technology area to be able to realise the Dual Camera sensor and its advanced fusion technology.

Smartphone cameras seem to be developing at such a fast pace; what developments could we see in the near future?
We believe mobile cameras will gradually become more and more like DSLR cameras with advanced features. However, due to the physical limitations with camera modules fitted inside a small mobile phone, we have to find new ways of compensating for a lack of changeable lenses using AI technology, sensing and computational camera technology.

In the further future we also speculate that 5G technologies will open the door for a new type of real-time app supported by more advanced and powerful server-side image processing.

Cyclists take a break outside a theatre

In which situations will people notice the biggest difference between the Xperia XZ2 Premium camera and other smartphones?
Xperia XZ2 Premium is designed to be a very competent camera in any situation. However, with its unique fusion technology, the most impressive difference can be seen when shooting photos or videos in low light. We believe the video ISO 12800 is currently the best on the market.

A lamp post shines in the dark

Finally, we asked Mashita-san and Goto-san for their top tips when it comes to shooting still imagery and video on the XZ2 Premium.

1) For optimal image quality, it is important to keep the camera perfectly still. Use a tripod or steady the camera against a stable object such as a table or a wall.

2) Use the self-timer to avoid camera shake when pressing the shutter button or screen.

3) If you are shooting in ultra-high sensitivity mode, keep a distance of one metre or more from the object you’re shooting.

Let us know how you get on shooting low light stills and video on the XZ2 Premium by sharing your best work with the hashtag #Xperia on Twitter!

For some video inspiration, take a look at this video of low light capture from the team at Sony: