How useful is a variable aperture on the new iPhone anyway?

The iPhone 18 Pro boasts a distinctive feature: a variable iris on its primary camera, enabling adjustable apertures ranging from f/1.48 to f/4. Several creators have expressed skepticism regarding this capability, arguing it lacks relevance due to the camera's compact sensor. This article aims to assess the practicality of this feature by comparing it to larger format cameras.

To evaluate its impact on depth of field, we'll examine how aperture diameter, subject distance, angle of view, and disc of confusion influence the outcome. With a focal length of 7mm, the entrance pupil measures 4.73mm at f/1.48 and 1.75mm at f/4. Considering the image area of 10mm by 7.6mm, similar to a 16mm cine frame, the iPhone 18 Pro's camera delivers equivalent depth of field characteristics as a 24mm lens on full-frame or a 12mm lens on Micro Four Thirds, with aperture ranges spanning f/5-14 and f/2.5-7, respectively.

Next, we'll delve into diffraction blur, a phenomenon influenced by the f-number multiplied by the enlargement factor to the viewed image size. The iPhone must enlarge images by 3.4 times compared to full-frame cameras and 1.7 times compared to Micro Four Thirds cameras to achieve equivalent diffraction blur. Consequently, the f-number range of f/5-f/14 for full-frame and f/2.5-7 for Micro Four Thirds systems aligns with the iPhone's capabilities.

Lastly, we'll consider the potential for image noise. Read noise, unrelated to exposure, remains a concern but appears consistent across modern 48MP sensors. Photon shot noise, influenced by light energy captured, is proportional to exposure times sensor area. Given the iPhone 18 Pro's base ISO of 32, its maximum exposure corresponds to ISO 100 on Micro Four Thirds or ISO 400 on full-frame, suggesting the variable aperture feature remains equally valuable as f/5-14 on full-frame or f/2.5-7 on Micro Four Thirds cameras.