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Nikon FX-Format CMOS Sensor

A design that incorporates everything that is possible—as the image sensor for our flagship camera

A major feature of this image sensor seems to be that it has been developed in-house. Are there any particular design advantages or difficulties associated with this?

Only after Tekeishi and his fellow engineers in charge of the camera body and lens had conducted numerous studies was the D3 completed.

Takeishi:

Nikon had already developed the LBCAST sensor in-house. However, developing a CMOS sensor represented a new challenge, and one troublesome aspect was the long and repetitive process of trial and error needed to achieve the target capabilities. However, we took advantage of the fact that the sensor was being developed in-house to investigate how best to match the CMOS sensor with the capabilities of the NIKKOR lens, and were thus able to bring out the full capabilities of the photographic lens. In this way we succeeded in obtaining a high level of image quality. Further, with the sensor being fitted to our flagship camera model, we have been able to incorporate functions and technologies that are effective for producing a high level of image quality without any compromise. Since top priority had been given to realizing high-performance and high-sensitivity features, we took all possible measures to improve performance-without regard to cost.

Were there any measures that you abandoned, or ones that were introduced in mid-stream?

Takeishi:

There were none that was discarded. Instead, there were supplementary measures that were added at the trial production stage. In particular, many improvements were made in order to enhance the sensor's high-sensitivity capabilities. The electronic signals had to be significantly amplified in order to increase the sensitivity; however, this also served to amplify unwanted noise, so we made numerous prototypes to improve performance and suppress this noise.

Which specific technologies led to high-sensitivity capability?

Takeishi:

The three main types would be light condensing, storage and low-noise technologies. The first of these-condensing-has been discussed earlier. This included increasing the pixel size and modifying the micro-lens. Light was now collected without loss. The second of these consisted of enlarging the photodiode and storing larger amounts of light in the form of electronic signals. This proved effective in increasing the dynamic range and achieving smooth gradations. The third was noise reduction. This was crucial, as the noise component has a major effect on image quality. The best way to improve the S/N ratio is to amplify at the signal source. However, we did this by putting an amplifier inside the sensor.

It is said that a proprietary method was also developed for reading out the amplified electronic signals.

Takeishi:

Yes, that's right. We adopted a 12-channel read-out with the aim of achieving higher speed and reducing noise. This would be like 12 people working in parallel. Even if they took their time individually, overall the work would progress quickly. Since electronic circuits operating at high speed have a tendency to generate a lot of noise, one person acting slowly to reduce noise would be effective. We didn't cut any corners on the subsequent signal transmission either. In order to remove noise that gets mixed in during transmission, we split the signal into two parts and transmitted them separately. Moreover, we used a coaxial cable to transmit the signals despite its higher cost. A coaxial cable consists of a line, which transmits the signal, surrounded by a conductor, and this serves to prevent external noise from contaminating the signal.

How much of a performance improvement does this represent over what existed before.

Takeishi:

In terms of ISO sensitivity, the performance achieved is two grades better than Nikon has ever managed before. The overall performance improvement of this CMOS sensor has been achieved by means of new image-processing technology as well as improved condensing and noise reduction.

Knowing what the user wants led to a great leap forward in sensor technology

How did the market react to the FX format when the D3 first came out?

Encouraged by positive feedback from
D3 users, Takeishi now looks to the
next challenge.

Takeishi:

Before the launch, there were rumors going around that Nikon had been unable to manufacture a full-size sensor. Against this backdrop, the announcement of an FX-format model caused astonishment in the market in that, in a positive way, it seemed to confound expectations. There was also a strong reaction to the fact that we had achieved a level of sensitivity as high as ISO 6400, which had never been attained before. Moreover, since the D3 is equipped with a number of new functions for enhancing image quality, such as Active D-Lighting and Lateral Chromatic Aberration Correction, it was hailed as a camera likely to satisfy high-end users.

What are the advantages of high sensitivity to the user, and how have actual users responded?

Takeishi:

Since telephoto lenses are frequently used in sports and news photography, we have received many requests from users who want higher shutter speeds, and we have been able to respond to this. Many have told us that they can now take more natural-looking shots, since the range of photography possible without the use of a tripod or a strobe (including city shots and night scenes) has widened.

Is the same CMOS sensor used on both the D3 and the D700? I would imagine that users might have concerns about this.

Takeishi:

The sensors used are completely identical. Since the D700 has a smaller body than the D3, there are differences in design due to the fact that the peripheral circuitry had to be smaller; however, the two cameras boast the same image quality.

Has there been any unexpected feedback?

Takeishi:

The HI 2 sensitivity setting is strictly for increasing sensitivity, and has generated little discussion in the past in regard to image quality. However, some photo magazines have pointed out that the image quality with this setting is as good as ISO 25600. This praise was most unexpected.

In what direction would you like to take sensor development in the future?

Takeishi:

I feel we did everything we could in this project. However, around the world, technological progress never ceases. Accordingly, I aim to respond to the diversifying requirements of our customers and develop products that go one step further. I want to keep pursuing ever more high-performance technologies.

Thank you very much for this interview.