They hide telephoto lenses worthy of professional cameras

Have you ever seen a 120mm telephoto lens? I took one to measure: it is more than 15 cm long. So 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 120mm example because that’s exactly the maximum focal length offered by the iPhone 15 Pro Max, released on Friday, September 22, 2023. 120mm instead of 77mm on the 14 Pro range. This leap was made possible thanks to the incorporation of what the manufacturer calls a “quad prism”. The result: optical zoom ranging from x3 to x5, equivalent to 120mm. It is very bright, with the diaphragm opening at f/2.8.

Periscope as on a submarine

The idea is that of a periscope as in a submarine: a set of lenses, coupled with one or more prisms, and small mirrors that deflect light, so that it is not limited by the dexterity of a phone. By rotating 90 degrees, light can pass through more lenses, this time across the width of the smartphone where there is much more space. This is exactly what Apple does with the “quad prism” in the iPhone 15 Pro Max, but by dispersing the light rays four times, to take advantage of a greater distance between the lenses and the sensor that records the image.

OPPO was the first manufacturer to offer this type of lens, with a 5X lens in 2017. In 2019, we found it at Huawei on the P30 with 5x optical zoom already. In fact, it has become a standard in the world of Android, where we find a periscope lens in Google’s Pixel 7 Pro and in the Samsung Galaxy S23 Ultra: low-light optics (f/4.9) in both cases, but offering an optical lens x10 zoom, in the case of Samsung.

OPPO, the precursor

Thus, the holy grail is this optical zoom, because smartphones are also equipped with digital zoom, but it simply artificially enlarges the pixels with, in return, a very rapid and obvious deterioration in image quality. Don’t let yourself be fooled by technical papers promising amazing magnification, such as 30x or more: if it is not specified that it is an optical zoom, perhaps enhanced thanks to the scope’s objective, you may be disappointed with the result.