It has become one of the essential features of smartphones: the ability of the telephoto lens to get closer to the subject being photographed. However, be careful not to confuse optical zoom and digital zoom.
Have you ever seen a 120mm telephoto lens? I took one to measure: more than 15 cm long. How do smartphone manufacturers manage to fit such a telephoto lens into the thickness of a cell phone: less than 1 cm?
Let’s stick with this example of 120mm, since this is precisely the maximum focal length offered by the iPhone 15 Pro Max, released this Friday, September 22, 2023. 120 mm instead of 77 mm on the 14 Pro series. This leap is made possible by the integration of what the manufacturer calls a “tetra prism”. Result: an optical zoom that goes from x3 to x5, which corresponds to a 120mm zoom. And it’s very bright since the aperture opens at f/2.8.
A periscope like in a submarine
The idea is that of a submarine-like periscope: a set of lenses coupled with one or more prisms, small mirrors that deflect the light so that it is no longer restricted by the subtlety of the phone. By rotating it 90°, the light can pass through more lenses, this time across the entire width of the smartphone, where there is much more space. That’s exactly what Apple is doing with its “tetra prism” in the iPhone 15 Pro Max, but by deflecting the light rays fourfold to benefit from a greater distance between the lenses and the sensor that captures the image.
OPPO was the very first manufacturer to introduce this type of lens with its 5X in 2017. In 2019 we found it at Huawei on the P30 with – already – an x5 optical zoom. In fact, it has become standard in the Android world since we find a periscope lens on the Google Pixel 7 Pro and on the Samsung Galaxy S23 Ultra: in both cases a low-light optic (f/4.9), but which has an x10 -Optics offers zoom, in the case of Samsung.
OPPO, the forerunner
The holy grail is actually this optical zoom, because smartphones are also equipped with a digital zoom, but this only artificially enlarges the pixels, which in turn leads to a rapid and clearly visible deterioration in image quality. Don’t be fooled by the specs that promise spectacular magnifications like 30x or more: if it doesn’t say it’s an optical zoom, probably optimized by a periscope lens, you risk being taken by the result will be disappointed.