Canon Applies To Patent Double - Sided Micro Lenses Designed For Better Edge Performance

Canon applies to patent double-sided micro lenses designed for better edge performanceCanon engineers have developed a new design for the micro lenses it uses on imaging sensors that it claims will reduce vignetting and false coloration at the edges of the picture. The new designs have a bi-convex lens that uses the upper surface to collect light and the lower to channel the light more effectively to the photodiode.
The patent application shows the lower face of the micro lenses with a convex surface featuring an off-center vertex. Canon says these would be placed at the edges of the sensor to direct light approaching from a steeper angle. The idea is to direct more of the light toward the photodiode than can be achieved with standard single-micro-lens designs.

As pixels have depth it can be difficult to channel light from the camera’s lens down the ‘well’ to reach the photodiode unless it approaches straight-on. When a pixel is positioned at the edge of the sensor array it becomes more difficult because light approaches from an extreme angle and can miss the photodiode, as the refractive index of the micro lens isn’t high enough to bend it directly down the well. Since certain colors experience different refractive indices, some wavelengths of light don't make it to the photodiode either. Thus, pixels outside the central area can report less light – and false colors – compared to those in the middle of the sensor.

Canon’s new dual micro lens design aims to take more control of the light as it enters and exits the micro lens, and to channel it in a more vertical direction down the well so that less is lost. This should in theory improve both vignetting and false coloration nearer to the edges of the image.