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Thanks to the dual rear cameras, smartphones can now take pictures with optical zoom, not just digital zoom
Until recently, it was an exclusive feature of cameras, whether it was an SLR or a small compact. This is due to a set of lenses and lenses that allow you to “zoom in” or “away” objects in the photo without affecting the image quality.
Now, however, optical zooms are also starting to make their way into the world of smartphones. Several manufacturers equipped their flagship models from late 2016 and early 2017 with this new feature, borrowed directly from the world of photography. At the moment, the optical zoom is limited (on the iPhone 7 Plus, one of the first models to implement it, the zoom factor is “only” 2X), but it is still functional for the purpose. Users can take detailed photos of mid-range subjects without losing image quality.
Difference between optical and digital zoom
The biggest difference between optical zoom and digital zoom is the quality of the pictures you take. In the first case, magnification is the result of the movement of the objective lenses, which “modifies” the incoming light before it touches the photo sensor (or the film in the camera, if you are using an analog camera). Thanks to this, it is possible to take pictures with a double-digit magnification factor (depending on the telephoto lens used, you can get 10- or 15x magnification) without the slightest loss to the image quality.
With digital zoom, the magnification of a subject is achieved programmatically: the camera (or smartphone) crops the unmagnified image until the user obtains the desired result. However, this comes at the expense of image quality: as the magnification increases, the crop factor for the original subject increases. To avoid getting images that are too small, the algorithms will “fill” the images with pixels similar to those that already exist, but this will make the image appear grainy. In short, be careful how you use the digital zoom: the end result may not be very satisfactory.
How optical zoom works in smartphones
Optical zoom in smartphones such as the aforementioned iPhone 7 Plus, Asus Zenfone Zen Zoom or OnePlus 5 is the result of using a dual rear camera. Both sensors have different focal lengths and allow the photography application to magnify the subject of the photo without affecting the quality. The optical zoom function is therefore quite simple: the smartphone will use one or the other sensor depending on the zoom factor required by the user. However, unlike cameras, the optical zoom on smartphones is “fixed”: you can have a zoom factor of 2x or 5x, but not in between. If you want to enlarge an object by 1.6x, for example, you will have to rely on software to manage and “merge” images taken by two sensors simultaneously.
Optical zoom is not the only zoom mode allowed by the dual rear cameras, however. If both sensors have different resolutions (for example, 20 megapixels and 12 megapixels), it is possible to use the so-called hybrid zoom: thanks to special image processing algorithms, the phone is able to obtain an enlarged image without loss of quality. All you have to do is “combine” photos taken at the same time by two lenses and you’re ready to go.
