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Smartphones with optical zoom: this is the trick behind them

Smartphones with optical zoomSmartphones with optical zoom work with a simple trick. What it should not be used for though, is unlimited zoom. Here, we tell you why.

Anyone who has even some understanding of digital photography knows that only optical zooms are good zooms. The digital zoom is the “baddie” because it worsens the image quality. For some time there has also been smartphones with optical zoom – that is what the manufacturers advertise, at least. But how does it work exactly if there is no focus ring?

Optical zoom now on smartphones thanks to two lenses

The answer is simple: with a trick. Current smartphones with optical zoom always have at least two lenses built in, meaning that they use a dual-camera, a triple camera or even more lenses. The manufacturers simply build in lenses with different focal lengths.

Smartphones with optical zoomGalaxy Note 9 Dual-Camera with 2x Optical Zoom

When you turn on the camera, you generally see the normal image angle of the 1st lens (often 26mm focal length). Usually there is a 2x or 3x button in the camera app that you can use to zoom in. The camera then does nothing but switch to the second lens with a larger focal length (usually 52mm).

Focal lengths and lenses in photography

The focal length of a lens is derived from the angle of view and the sensor size of a camera. Photographers speak of standard lenses, telephoto lenses and wide-angle lenses. The decisive factors are the angle of view and the focal length:

  • Regular lens, with an around 50mm focal length on a 35mm camera. The image section most closely matches the human field of vision.
  • Wide-angle lenses: about 8 to 50mm focal length, catch more than the human field of view can see.
  • Telephoto lenses, about 50 to 600mm focal length (scale is upwards but basically open). Reduce the angle of view, thus bringing distant objects visually closer.

Of course, there are other subcategories here, such as ultra-wide-angle lenses with a particularly short focal length (and, conversely, a very wide field of view). For photo beginners most popular are telephoto zoom lenses or so-called Street-zoom lenses. With them you can adjust the focal length. In most cases, the image angles of all three lens types are covered a bit.

Whether a lens with 50mm focal length is a normal lens, by the way, depends on the camera type used. Only with full format cameras are 50mm the normal focal length. For cameras with smaller sensors (including smartphones), the normal focal length is below, and 50mm are already considered as a light telephoto.

Zooming: yes, but not stepless!

In digital cameras, turning the lens wheel changes the position of the lenses inside a telephoto zoom lens. This is not the case with the stationary lenses of a smartphone. And that’s why you should not zoom in on a smartphone. If you zoom in on a subject about 1.6 times, here is still the first camera lens active. It can not change the focal length and angle of view, so it can only zoom in with the worse digital zoom.

Smartphones with optical zoom

Smartphones with optical zoomIn any case, use the offered zoom levels of the camera app!

Important to know: The different lenses of a camera do not work together. It’s an either-or situation. In the case of smartphones with optical zoom, you can definitely use the zoom levels: 1x, 2x or – where available – 3x.

Examples of smartphones with optical zoom

iPhone XS

Smartphones with optical zoomThe current iPhone XS uses a dual-camera (just as with its sister model, the iPhone XS Max and former iPhone X, iPhone 8 Plus and iPhone 7 Plus). Both lenses of this camera have various focal lengths.

  • iPhone XS: 1st camera lens: 26mm focal length (wide angle), aperture f/1.8, 1/2.55-inch sensor, pixel size: 1.4µm
  • iPhone XS: 2nd camera lens 52mm focal length (tele), aperture f/2.4, 1/3.4-inch sensor, pixel size 1.0µm

As you can see, the 2nd camera lens has a 52mm focal length, making it double as much (2x) as the first one. As such, optical zooming can be done just by turning it on. As an example, we have also listed the other features of the camera, and they are not unimportant:

The 2nd camera lens on the iPhone XS has a smaller aperture (less light output), a smaller sensor (less detail) and smaller pixels (also less light reception). That means that the 2nd camera lens in the iPhone XS is somewhat worse than the first, and consequently their photos also. Optical zoom is linked with a loss of quality, even if it does not look as tragic as it would with a digital zoom.

Huawei Mate 20 Pro

Smartphones with optical zoomHuawei has even built a triple-camera into their new Mate 20. Triple does not yet mean that you automatically have three times optical zoom. It depends on the functions of the camera. The optical zoom on the Mate 20 camera should even have five times optical zoom. But that is also just a trick calculation, even if it is a clever one:

  • Huawei Mate 20 Pro: 1st camera lens: 27mm focal length (wide angle), aperture f/1.8, 1/1.8-inch sensor
  • Huawei Mate 20 Pro: 2nd camera lens: 16mm focal length (ultra-wide angle), aperture f/2.2, 1/2.7-inch sensor
  • Huawei Mate 20 Pro: 3rd camera lens: 80mm focal length (tele), aperture f/2.4, 1/4-inch sensor.

The five-times optical zoom in the tele lens of the Mate 20 Pro is only relevant to the built-in ultra-wide angle (5x16mm=80mm). In comparison to the regular lens, the zoom would “only” be triple. Here too, the telephoto lens has the worse properties in terms of light and detail yield.

Samsung Galaxy S9+

Smartphones with optical zoomSamsung advertised its new Galaxy S9 as having a dual-aperture, which surpassed that of the naked human eye. That does not have any impact on the optical zoom, by the way; I also only had the larger Galaxy S9+ given to me (2x). This one also only has two camera lenses:

  • Samsung Galaxy S9+: 1st camera lens: 26mm focal length (wide angle), aperture f/1.5-2.4, 1/2.55-inch sensor, pixel size 1.4µm
  • Samsung Galaxy S9+: 2nd camera lens: 52mm focal length (tele), aperture f/2.4, 1/3.6-inch sensor, pixel size 1.0µm

Smartphones with optical zoom: what a sham!

The 2nd camera lens in the iPhone XS and the Samsung Galaxy S9+ has a 52mm focal length. Now just imagine: a smartphone manufacturer can only build in one camera with 52mm focal length. With it you cannot actually zoom, but you have the same tele-effect. Most providers opt for a wide angle for their main camera, because that is where the most light will be received.

To summarise:
  • Optical zoom in smartphones can only be realised with dual or multiple-lens cameras.
  • The inverse argument that every dual or multiple-lens camera has an automatic optic zoom is wrong! Sometimes various lenses have other functions, such as for split monochromes and colour photography.
  • Optical zoom in smartphones works between cameras with different focal lengths by toggling the phone.
  • The zoom factor of the 2nd lens is relative to 1. If the first one has a particularly large wide angle, the zoom factor of the tele camera goes higher accordingly. A five-time-zoom comes closer to the object than a triple-zoom.
  • The lenses do not work together. You can zoom limitlessly, but once you hit, for example, 1.8-times, the worse digital zoom replaces it. Use the offered zoom steps from the camera app, as it does this for you
  • Tele-recordings blur out faster. The tele camera should then also, ideally, have optical image stabilisation.

Conclusion

The optical zoom on smartphones is not comparable to the tele-zoom lenses in digital cameras. Because it switches between different lenses and focal lengths, zooming is not completely hassle-free. Furthermore, because the tele cameras are always less well equipped than the main camera, zoomed pictures are also a bit worse, so again connected with a loss of image quality.

Nonetheless: smartphones with optical zoom do have some advantages. Because single-lens cameras generally only use wide angle, you can get closer to the motive. And in this way, it is also better in quality than a digital zoom.

This could give someone the idea to keep their heavy mirror reflex camera with a tele zoom lens in a drawer. But the fact that you can take many detail-rich photos with the latter should be clear to everyone.

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