Why Do Smartphones Have So Many Cameras?
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In cameras for shooting different plans, interchangeable lenses or optics with variable focal length are used. However, a smartphone is a compact device. Zoom lenses would significantly increase the size of the camera module, so most smartphones use optics with a fixed focal length. Multi-camera designs solve the main issue—they provide the flexibility to shoot diverse scenes, whether landscapes, portraits, or distant objects from the user. Additionally, having different sensors allows for collecting various auxiliary data—artificial intelligence algorithms improve the photo based on this data.
1. Main (rear) camera
In current-generation smartphones, the number of main camera lenses usually varies from two to four. The golden mean is a triple camera module combining a leading image sensor, an ultra-wide-angle, and a telephoto lens in one package. Such an inseparable trio is often found in flagship camera phones. Simpler models feature various configurations of "multi-eyed" cameras—their quality and purpose vary depending on the specific implementation.
1.1. Leading (standard) module
The main camera has the best characteristics among all camera modules. It is based on large image sensors, boasts high resolution (up to 200 MP, more often around 50 MP), and is equipped with bright optics (often less than f/2.0). The leading camera is usually equipped with a wide-angle lens with an equivalent focal length within the range of 25 – 35 mm—these values are optimally suited for comfortable shooting of any everyday scenes.
For instance, in this sensor aboard the Nubia Z70 Ultra model, variable aperture optics are provided.
It is in the leading sensor that advanced technological developments are implemented—variable aperture (as in smartphones Honor Magic 7 Pro or Nubia Z70 Ultra), optical or even matrix stabilization of the image, and the ability to record ultra-high-definition video (up to 8K). The remaining camera modules essentially complement the main sensor with their presence and are intended for comfortably performing auxiliary tasks.
1.2. Ultra-wide / super-wide camera
The ultra-wide camera, as you can guess from the name, is equipped with optics with a broader field of view than the leading image sensor. Enlarged angles of view are useful for shooting landscapes, architecture, room interiors, and group shots. If the main camera of a smartphone has a view angle of about 75 – 80°, then the super-wide is approximately 120 – 130°. Thus, more of the surrounding space fits into the frame.
The matrices in ultra-wide cameras are smaller than in the leading camera module, and the aperture is "darker." Also, note that the super-wide sensor distorts perspective—this is particularly noticeable when shooting at a short distance. Because of this, the super-wide camera is not the best choice for portrait photography, as it will distort the proportions of people in the frame (the camera unnaturally stretches the figure). However, distortions when shooting landscapes, architecture, and panoramas are excellently corrected by AI image enhancement algorithms (if the smartphone supports them).
1.3. Telephoto lens
The telephoto lens is a specialized long-focus camera module for shooting distant objects. Telephoto lenses are equipped with optics with a narrow field of view and an equivalent focal length of over 60 mm (the exact value depends on the implementation). In fact, the telephoto lens is used to magnify an image without losing quality. It helps shoot timid wildlife, distant portraits, architecture elements, etc.
Optical scaling of the image ensures a win in detail since digital zooming results in reduced image quality. However, true close-up is achieved only to a fixed degree (2x, 3x, 5x, rarely up to 10x). This is due to the inability to install a mobile lens assembly in the smartphone's slim body, which could change the focal length on the fly.
Because of the optical design features, telephoto cameras already take up a lot of space in the mobile device's body. In advanced camera phones, telephoto lenses are placed perpendicular to the body, and light hits their matrix by the refraction of rays through a special mirror. Such cameras are commonly referred to as periscopic.
When shooting, smartphones may use the main image sensor and the telephoto lens to capture details from multiple cameras simultaneously. The information obtained from them can be used to intelligently enhance the photograph using AI algorithms—often implementing the so-called hybrid zooming this way. More information about this is available in the article "Software, optical and hybrid zoom in smartphone cameras. What's the difference?".
1.4. Macro lens
A separate macro lens is quite a controversial solution. No, the idea is indeed good— the macro sensor allows focusing on small objects from a very close range, measured in just a few centimeters. This is potentially great for subject photography. In practice, however, the devil is in the details—macro cameras are often equipped with small matrices with resolutions ranging from 2 to 5 MP, providing mediocre photo quality.
The macro lens in the smartphone's main camera is unlikely to be used regularly, yet for some scenes, it will be very handy. For instance, the macro camera will allow taking a close-up of a small drop of dew on a blade of grass or various bugs and beetles.
1.5. Microscope camera
A modernized version of the macro lens with an impressive magnification of up to 30x or even 60x. The microscope camera serves to capture microscopic objects and textures, which are impossible to see with the bare eye. The practical purpose of this camera is small, but it still stands as a kind of unique feature in the multi-camera constructions of a smartphone.
The flaws of the microscope camera are almost the same as in regular macro sensors: low matrix resolution, lack of autofocus, and an extremely shallow depth of field. However, the microscopic sensor is often complemented by a ring flash with a constant mode of lighting.
1.6. Night vision camera
The night camera allows you to "see" in complete darkness. The night vision module is equipped exclusively in rugged smartphones, and it is used for photo and video shooting in conditions of partial or total absence of ambient light. LEDs for IR illumination are utilized to light up the scene, reaching distances of 8 – 10 meters.
Night cameras do not shine in terms of supreme image quality, and the trade-off for shooting them is a black and white image. Night vision sensors are usually supplemented with bright optics.
1.7. Thermal camera
A thermal camera is another feature found in indestructible smartphones with reliable protection against shocks and falls, dust, and water. It captures images in the infrared spectrum. Thermal cameras in smartphones have a relatively narrow specialization—such a camera is used to detect heat leaks, track the route of heating pipes in the floor, or even find a black cat in a dark room.
The thermal sensor may rely on specialized software for interpreting results and creating a thermal map of the space. Its main application area is construction and repair work. Meanwhile, a thermal camera may be beneficial in hunting or military applications.
1.8. Black-and-white (monochrome) sensor
At the dawn of multi-camera constructions in smartphones, the leading image sensor was often supplemented by a monochrome sensor. Nowadays, it almost doesn't appear, but the black-and-white camera is worth mentioning. In the conventional color matrix, each pixel consists of several subpixels responsible for its color component. In the monochrome sensor, this structural need is absent. As a result, black-and-white matrices contain larger pixels, which enhances the overall sensitivity of the sensor.
yet they were once quite widespread.
Practically speaking, a black-and-white camera provides images with less noise in low ambient light. This data is also used by the main camera to minimize noise in photos. Additionally, a monochrome sensor allows more information to be captured from highly illuminated or overly dark areas of the image, which is necessary for a correct result in HDR shooting mode. In practice, the significance of the black-and-white sensor has considerably diminished with the development of intelligent photo processing algorithms via AI—the need for a monochrome module has simply disappeared.
1.9. Depth sensor / Time-of-Flight sensor (ToF camera)
The auxiliary camera is implemented both technically and programmatically in various ways. Often, it is represented by a depth sensor or a Time-of-Flight (ToF) sensor. These cameras operate similarly to sonar, where light is used instead of sound. Photographs in the classic sense are not taken with these cameras—they serve to determine distances to objects.
Data collected from the depth sensor is used for subsequent in-camera post-processing of the photograph. Primarily, the information will be useful for separating the subject from the background with a beautiful bokeh effect (for instance, in portrait photography). In implementations with a separate LiDAR sensor, the auxiliary camera can serve for augmented reality (AR) and high-precision 3D modeling of the surrounding space. However, such systems are quite rare. They work as a special sensor that emits light in the infrared spectrum and then records the speed at which it reflects off the object, creating a 3D model.
In most cases, the auxiliary sensor is not that sophisticated and merely assists the main camera lenses in creating images with proper depth of field.
2. Front (selfie) camera
Selfie cameras in smartphones are still single. The exception to the rule is rare mobile device models with dual front cameras. One camera is wide-angle, and the other is super-wide with an extended angle of view. Why is this needed? Simply for group selfies. The secondary front camera carries no other significant purpose.
In some cases, the wide-angle lens is equipped with a depth sensor (or ToF sensor), enabling the selfie camera to capture great portraits with an impressive background blur.
In Apple smartphones, the selfie camera is accompanied by a specialized TrueDepth sensor that uses infrared scanning for the Face ID unlocking system. This is why iPhones used to have a distinctive "notch". In current generations, it is designed more elegantly, but the front camera still occupies significant space in iPhone screens.
Notable implementations of selfie cameras include the under-display (hidden) design. The selfie camera module is hidden under the matrix pixels, which turn off when the selfie camera is activated. This makes the lens on the front panel almost invisible. Such a design doesn't come cheap, so it's quite rare.
3. Conclusion
No matter how many cameras there are in a smartphone, remember—quantity doesn't directly affect photo quality. A budget phone won't shoot at the flagship level just because both have triple cameras. More important is the quality of the matrix and optics of the main sensor, and it's worth understanding which cameras you truly need.
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