The zoom performance of smartphone cameras has improved dramatically in the last couple of years or but still lags behind conventional cameras, despite dedicated tele lenses pretty much being the norm on high-end smartphones these days. It’s fair to say that overall, zooming on a smartphone camera is at this point still a bit of a compromise, but that could soon change, though.
Chinese camera module supplier O-Film has demonstrated a periscope-style smartphone lens that provides an optical zoom range of 85-170mm (35mm equivalent). This, in theory, should provide a more consistent image quality across the zoom range than current models.
Most tele cameras inside flagship smartphones provide magnification factors between 3x and 10x compared to the primary camera, but speaking about ‘zoom’ factors in this context is slightly misleading. In most instances, the tele camera use lenses with a fixed focal length and computational methods are used to deliver the stated zoom ratios.
At intermediate zoom settings between primary and tele cameras most models use digital zoom/cropping and other computational imaging methods that combine image data from both cameras to create an output image. This Samsung system illustrated in the video below is a good example:
In practice, this means that if you want the best possible image quality you will have to shoot at the native focal lengths of either the primary or tele camera. At intermediate settings your images will, at least under close inspection, almost certainly show a loss of detail and/or a range of fusion artifacts. For example, on some models the level of detail at the center of the frame is high because this portion of the image is captured with the tele camera. Often a lack of detail is visible towards the edges, though, as these areas of the frame are ‘filled’ with digitally zoomed image data from the primary camera.
O-Film’s solution should avoid these kind of image quality inconsistencies by providing optical zoom across the entire range of focal length from 85-170mm (35mm equivalent). The module’s aperture ranges from f/3.1 at the wide end to f/5.1 at the maximum tele setting, which is pretty much in line with the apertures on most fixed-focal-length tele cameras. At only 5.9mm the module is also impressively thin which means it should fit into the sleek form factors of most current flagship devices.
The zoom range of the O-Film module is roughly equivalent to a 3-7x zoom factor but the company claims it can also provide 3-5x, 5-8x and 3.5-9.5x variants.
Like other periscope style lenses with a fixed focal length, such as the one found in Oppo’s 5x camera module, the O-Film module uses an optically-stabilized prism to divert incoming light onto the image sensor. What’s different in O-Line’s module is a piezoelectric motor that drives a module with three lens groups to adapt the focal length. The autofocus mechanism moves with the lens elements.
If the new system works as advertised in the near future image quality on smartphones could be much more consistent across the zoom range than it is now, offering greater flexibility to mobile photographers. Unfortunately, there is no word yet on when we might see the zoom in a production smartphone.
Chinese smartphone maker Oppo previously used a periscope lens with a fixed focal length and computational processing to provide a ‘5X’ zoom, but this approach combines a wide-angle prime with a periscope lens that physically zooms. This combination means the zoom camera doesn’t need to provide wide-angle focal lengths and instead is able to provide just the telephoto range, which simplifies the optical design challenge.
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