Light that enters the camera through a NIKKOR lens is converted to an electrical signal by photodiodes embedded in the imaging sensor. When this happens, two major factors directly influence the quality of the final image, particularly in terms of dynamic range and ISO sensitivity — how efficiently light can be converted into an electrical signal, and how much light can be stored as an electrical charge in each pixel.
For the D3, with its large pixel size of 8.45 x 8.45µm, we worked relentlessly to develop an optimal sensor structure that would collect the maximum amount of light. With both Nikon FX and DX format imaging sensors, closely related methods are applied to concentrate and combine the light to improve image quality. The D3’s Nikon FX format imaging sensor offers a particularly wide ISO sensitivity range of ISO 200 to ISO 6400 at normal settings for unprecedented image quality with very little noise, plus rich tonal gradation and color reproduction. When needed, the ISO sensitivity range can be expanded to an equivalent of ISO100 to ISO 25600, for even greater freedom in exposure control, maximizing the potential of any light available at the time of shooting.
The Nikon FX format imaging sensor is 36.0 x 23.9mm, with each pixel measuring 8.45 x 8.45µm — approximately 2.4 times larger than those used in the D2x. This means that each D3 pixel is able to collect much more light. As a result, the Nikon FX-format imaging sensor provides higher ISO sensitivity and receives more light from low-lit subjects. This, in turn reduces noise at high ISO settings. And because each pixel carries more electrical charge, it provides a wider dynamic range.
The photodiodes on the sensor are surrounded by miniature electrical connections. Even if a photodiode is large, this advantage is cancelled out if it is surrounded by excessive circuitry. Therefore, it’s essential to minimize the circuitry in order to secure a larger light-sensitive area so that each photodiode obtains more light. Nikon designed and manufactured the ultra-microscopic circuitry around the photodiodes in such a way as to maximize this light-sensitive area and achieve the extra capacity needed for a larger pixel size. Because electrical amplification of received light is maintained at a minimum, the deterioration of signal-to-noise ratio caused by amplification can also be minimized, which has a major beneficial impact on image quality.
The Nikon D3’s image sensor incorporates various mechanisms for collecting light efficiently and channeling it to the photodiodes. One such mechanism is the newly adopted gapless on-chip microlens, which features less space between lens elements and minimizes light loss. Furthermore, the structure of the on-chip lens maximizes the performance of NIKKOR lenses so that incoming light reaches the photodiodes without unnecessary loss. The light-receiving ratio is also enhanced by the reduced size of the circuitry layer (signal transmission path) and its slim design, shortening the distance between the circuitry layer and each photodiode.
In addition to the aforementioned mechanisms for improving the light-receiving ratio, a variety of simulation tests were conducted repeatedly to optimize the on-chip lens. The imaging sensor contains several elements other than photodiodes, including a circuitry layer, and if these internal elements are not configured properly, vignetting may occur. Since the incident angle of light differs with each lens, Nikon came up with methods to evaluate individual NIKKOR lenses in order to further optimize the on-chip microlens.
With its larger pixel size, mechanisms to increase the light-receiving ratio and the efficiency of the noise-reduction amplifier, the D3 has achieved an unprecedented signal-to-noise ratio. Factors that contribute to noise in the image sensor manufacturing process have also been reduced.
