Samsung & Apple: Variable Aperture Cameras – A Telephoto Lens Win?

Rumors suggest Apple and Samsung are considering variable aperture technology for the main cameras of their upcoming smartphones. While this feature has appeared in phones from companies like Xiaomi and HONOR, a growing consensus among industry observers is that variable aperture is better suited for telephoto lenses than wide-angle main cameras.

What is a Variable Aperture?

Most smartphone cameras have a fixed aperture – the opening that controls the amount of light reaching the image sensor. A variable aperture, however, allows the camera to adjust the size of this opening. This is typically expressed as an f-number; a lower f-number (e.g., f/1.6) indicates a wider aperture, letting in more light and creating a shallow depth of field (blurred background). A higher f-number (e.g., f/4.0) indicates a narrower aperture, increasing the depth of field and bringing more of the scene into focus.

Phones like the HONOR Magic 7 Pro and Xiaomi 14 Ultra have already implemented variable apertures on their main cameras, often offering two distinct aperture settings. This allows for greater flexibility in different shooting conditions, optimizing for low-light performance or maximizing depth of field.

Why Telephoto Lenses Benefit More

While a variable aperture on a main camera offers benefits, the impact is significantly more pronounced on telephoto lenses. This is due to the physics of depth of field and light gathering. Depth of field decreases as focal length increases. At a typical 24mm equivalent main camera, shifting from, say, f/1.6 to f/2.8 results in a subtle change in background blur. However, at 70-120mm equivalent – the typical range for smartphone telephoto lenses – that same aperture shift produces a much larger change in subject isolation and bokeh (the aesthetic quality of the blur).

The effect is quantifiable. As explained by photography resources like Cambridge in Colour, blur disk size scales with both focal length and f-number. Longer lenses amplify this effect, meaning a variable aperture has a more noticeable impact on the aesthetic quality of the image.

Beyond aesthetics, a wider aperture on a telephoto lens significantly improves low-light performance. Consider Apple’s iPhone 15 Pro Max telephoto lens, which operates at f/2.8. In dimly lit environments, the camera relies on longer exposures and noise reduction. Opening the aperture to f/2.0 nearly doubles the light intake – a 96% increase – reducing the need for long exposures and aggressive noise reduction. Similarly, Samsung’s Galaxy S24 Ultra, with its f/3.4 5x telephoto module, would see an immediate improvement in image clarity with a wider aperture.

Conversely, stopping down the telephoto lens (increasing the f-number) can also be valuable, allowing for greater depth of field in situations where it’s desired.

The Current Landscape and Challenges

Smartphone manufacturers have been increasingly adopting larger, one-inch camera sensors. However, these sensors have often been paired with fixed, wide apertures, sometimes leading to issues with shallow depth of field and focusing challenges. The Xiaomi 14 Ultra addressed this by combining a one-inch sensor with a variable aperture, demonstrating the potential of this combination.

However, implementing a variable aperture on a telephoto lens presents a significant engineering challenge. Telephoto and periscope camera modules are already complex and space-consuming. Adding a variable aperture mechanism to these modules increases both the complexity and the physical size of the camera bump.

Despite these challenges, the benefits of a variable aperture telephoto lens are compelling. It offers improved low-light performance, greater control over depth of field, and the ability to create more aesthetically pleasing images, particularly in portrait photography. The ability to adjust the aperture allows for more natural-looking bokeh and reduces the reliance on software-based blur effects, which can sometimes produce inaccuracies.

While the engineering hurdles are substantial, the recent advancements in smartphone camera technology – including the implementation of periscope lenses, large sensors, and variable optical zoom – suggest that a variable aperture telephoto lens is not an insurmountable goal. The potential gains in image quality and creative control make it a worthwhile pursuit for manufacturers like Google, Samsung, and Xiaomi.