Digital imaging sensors are traditionally small, flat devices that convert images, which are focused onto the sensor by a lens of some sort, into an electronic signal that can then be processed in numerous ways. With very few exceptions, every digital sensor in use today is flat. However, in a few year's time, that may not be the case, as Sony's device manager Kazuichiro Itonaga recently showcased two new curved CMOS sensors, one a 43mm full frame sensor and the other a much smaller 11mm 2/3 size sensor. These new sensors are reportedly up to twice as sensitive as traditional CMOS sensors, and they have the potential to make our lensing systems simpler, faster, and sharper.
In order to understand why the development of curved sensors is a significant one, it's important to first understand some of the inherent limitations of flat sensors. First up is the issue of field curvature. In this excellent article from DPReview, Rishi Sanyal breaks down what field curvature is and why lenses need complicated optical corrections in order to combat field curvature when projecting onto a flat surface.
Field curvature results from the fact that the effective focal length light rays experience decreases the more off-axis light rays are from the lens' optical axis (the optical axis is defined by a line running from infinity through the center of the lens). In other words, the more off-axis a light ray is, the further in front of the focal plane (defined by focused on-axis rays) it falls.
Enter Sony's new curved sensor. Theoretically, this curved sensor would allow lens manufacturers to create simpler lenses (with fewer elements and larger maximum apertures) that work with field curvature instead of against it, since light hitting the lens from oblique angles wouldn't need to be optically corrected in order to be projected onto a flat imaging plane.
Beyond the possibility of simpler and higher performance lensing systems, curved sensors also have the potential to offer higher performance than their flat counterparts. Apparently, the manufacturing process for these sensors, which is done by a custom machine that bends flat sensors into a convex shape, actually increases the inherent performance capabilities of the sensor. In this article from IEEE Spectrum, Rachel Courtland describes how curved sensors have the potential to be more efficient.
Photodiodes at the periphery of a sensor array will be bent toward the center, which means light rays will hit them straight on instead of obliquely. What's more, the strain induced on a CMOS sensor by bending it alters the band gap of the silicon devices in the sensor region, lowering the noise created by "dark current" — the current that flows through a pixel even when it is receiving no external light.
According to Sony's engineers, the curved sensor that they debuted last week is 1.4x more sensitive at the center of the sensor and 2x as sensitive at the edges, which means that the low-light potential of these sensors is mind-blowing, especially when paired with any newly designed large aperture optics designed specifically for these curved sensors.
Of course, there are some drawbacks to curved sensors as well, chiefly that their only applications -- at least at this point -- are in fixed lens cameras, since the curvature of the sensor has to match the field curvature of the lens projecting onto it. In order for interchangeable lenses to work in an imaging system with a curved sensor, the sensor itself would also have to be easily interchangeable, something which would likely be too time-consuming for most photographers and filmmakers.
In the near future, we're not likely to see curved sensor technology make its way into the filmmaking world, largely because of the issue with interchangeable lenses described above. However, the 43mm full-frame sensor could very well find a home in cameras like Sony's RX1, and maybe even some of Sony's fixed-lens camcorders. The 11mm sensor is more likely than not going to find its way into smartphones and similarly sized imaging devices.
What do you guys think about Sony's new curved sensor? Will this technology have a significant impact in the worlds of photography or filmmaking? Let's hear your thoughts down in the comments!