Understanding the Function of a Periscope Lens in Your Smartphone: Explained

Ever since the first camera was put in a mobile phone, manufacturers have been in a perpetual arms race to include the best camera system on their devices. This has been great for consumers when almost every phone available today can take decent photos (especially compared to the 1MP cameras we had in the early days). The cutting edge of mobile photography mostly lies on the computational side of things, but one hardware advance, in particular, is changing what we can do with our smartphone camera and how we use it: the periscope camera. Let’s explore what this camera is all about.

To understand what a periscope camera does and the problem it solves, we have to know a little bit about how cameras work. At the most basic level, lenses focus light onto a camera sensor (or film in some cases), which converts that light into an image. Most smartphones come with a camera that has a wide field of view because, in general, people want to capture as much as possible in their photos. Still, the physical limitation of the depth of the phone limits its camera’s maximum focal length (and by extension its zoom and field of view).

To achieve a greater zoom, a camera needs to have a longer focal length. This is why the zoom lenses you see on full-body cameras tend to be longer than their wide-angle counterparts. Some phone makers tried to overcome limited focal lengths by integrating an optical zoom lens directly into phones. Samsung gave this a go with its Galaxy Zoom, which had a telescopic lens that could achieve 10x zoom. For whatever reason, camera/phone hybrids never caught on, and they faded away into the footnotes of smartphone history.

Although the first mainstream foray into mobile zoom photography fell flat, the dream lived on in a concept known as folded optics. As anyone who’s stared at a mirror will know, light doesn’t necessarily travel in a straight line; its path can be bent, warped, or diverted depending on the objects it encounters. Modern smartphones take advantage of this by taking a note from periscope design.

The idea behind periscope cameras is simple. Whereas previous mobile zoom lenses extended out from the phone body, a periscope camera’s zoom lens extends through the length or width of the phone’s interior and uses a prism to bend the light in a manner similar to a submarine’s periscope to align the aperture (where the light comes in) with the other camera sensors.

Even though Samsung was trying to make telescoping zoom lenses a thing in 2013, the periscope mobile camera had already been released and quietly forgotten 9 years prior. In 2004 Sharp debuted its 902 flip phone. It retailed for $200, had a whopping 2MP camera (which was actually quite large for the time), and had the first periscope camera in a mobile phone. Sharp didn’t manage the 902’s distribution and marketing very well, so its 2x zoom barely left a ripple in the pond of smartphone history. The 2015 Asus Zenfone Zoom was the next phone to include a periscope camera, which had a 2x zoom, 13MP sensor, and the latest in autofocus and image stabilization technology. Despite favorable reviews, the ZenFone Zoom did not move the market nor drive widespread implementation of periscope cameras.

The sea change for periscope cameras came in 2019 when the Huawei P30 Pro dropped with 5x zoom and a top-of-the-line image processing pipeline. The P30 Pro changed the conversation overnight, forcing competing OEMs to follow its trail. Today, you can find periscope cameras on top-tier smartphones like the Galaxy S23 Ultra and the Pixel 7. And Apple is finally getting in the periscope camera game with its iPhone 15 Pro Max.

Periscope camera modules still have some significant hurdles to overcome. First of all, they’re expensive, not just in terms of how much they cost, but also in terms of how much space they take up. Periscope cameras cost more than standard camera modules with similar sensors because they have more parts and are made with more precise engineering. They also take up more space in the phone, meaning phones either have to be made thicker and heavier or sacrifice other hardware features like headphone jacks or storage.

Despite having a larger hardware footprint within the phone’s body, periscope cameras actually have less room for their camera sensors. Traditional camera modules place the image sensor flat against the rest of the phone’s components, with lots of room for larger sensors. But, because of the way periscope cameras reflect light into the phone, their sensor must be rotated so that it’s perpendicular to the phone’s components, and thus, limited by the depth of the phone. This puts a hard limit on the pixel density of the sensor and therefore how much light it can collect (significantly impacting its low-light performance).

Another problem inherent to zoom photography in general is image stabilization — the more you zoom in on an object, the more ambient motion becomes apparent. Our bodies are never still, and even though this minuscule motion is virtually invisible in a wide-angle shot, it will turn zoomed-in shots into a blurry mess if the exposure is too long.

As folded cameras grow increasingly commonplace, one feature that will become more standard is the ability to bend the path of the light more than once to allow the periscope image sensor to be placed in the same orientation as other sensors, offering increased zoom capability and better image quality. This feature will raise the cost of production, but it will allow for a larger sensor. It’s the approach Apple is taking with the iPhone 15 Pro Max, what Apple calls a “tetraprism,” which essentially bends the light four times between the aperture and the image sensor.

Another trend to look for in mobile zoom technology is continuous optical zoom. Most smartphone camera modules have a fixed focus, so when you zoom in or out, your phone’s actually using image processing tricks to make the transition between your wide-angle camera and your zoom camera appear smooth. Future periscope camera modules will feature moving elements to achieve a range of continuous zoom. You can get a taste of this tech now with the Sony Xperia 1 V. Sony’s monopoly on the continuous optical zoom niche won’t last for long, though, because in December 2022, LG Innotek (one of the big camera module makers) announced its new periscope camera module will be able to achieve optical zoom between 4 and 9x.

Even though periscope cameras have had a moment over the past few years, they haven’t entirely cemented their place as a must-have item for smartphone enthusiasts. In the near term, these camera systems will probably remain exclusively on high-end phones, but as more are produced, and the economies of scale drive the prices down, it’s likely that these camera systems will start to appear in non-flagship phones where the market will decide if they sink or swim.