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Exposure Metering

Control of light is critical to heightening photography's expressive power. Nikon's light metering technologies are valued for their superior precision throughout the spectrum of lighting conditions. An engineer who has been developing these innovations for years offers insight into these technologies.

MURAMATSU, Masaru
Junior Executive Staff, Advanced Digital Imaging Laboratory,
Imaging Company, Nikon Corporation
PROFILE:
Joined Nikon Corporation in 1982 and assigned to the Camera Development Division. Involved since then with basic technologies for metering, AF, anti-vibration and other functions. Enjoys shooting with D100, FM2 and COOLPIX4200 cameras, especially to shoot friends and landscapes he encounters when indulging his passion for mountaineering.

Toward higher-precision exposure control.
Nikon technological innovation keeps leading the way.

Nikon metering technologies have a reputation for establishing standards of outstanding precision. Before going into details, can you give us a very brief history of these advances?

MURAMATSU, Masaru:

Our first metering system was an exposure meter using external sensors, for the Nikon F. In those days, other camera makers made external sensors link only with the shutter speed. But to optimize utility, Nikon devised a system of external sensors linked with both aperture and shutter speed. After mainstream metering technology moved to TTL (through the lens) systems, Nikon developed its “Center-weighted Metering” system, concentrating sensitivity in center frame, so images would not be overly influenced by the sky's condition, for example. Most cameras followed in featuring this system, which became a standard among TTL metering systems for a while. Nikon continued to use this system up to the introduction of the F3.
Then, for even greater precision, the company developed a five-segment matrix metering system, in which the frame was separated into five segments for measuring light intensity and a microcomputer in the camera calculated optimal exposure value. This feature, called “Automatic Multi-Pattern” metering for the Nikon FA, was the first of its kind. Then, for the F90, we advanced this system to use eight segment patterns. We're still on a never-ending quest to improve this metering system continually. For the F5, we developed a system using a CCD image sensor capable of capturing images by itself, as a metering sensor does. In our current camera lineup, we still feature the “3D-Color Matrix Metering” system using a “1,005-pixel RGB Sensor.”

Among the many exclusive technologies, the “1,005-pixel RGB Sensor” which you referred to seems particularly great. It has been the core element of the Nikon metering system for a while, from the introduction of the F5 up to the present, and is included in many film and digital SLR cameras. What advantages does it offer? What makes it a unique feature exclusive to Nikon?

The “1,005-pixel RGB sensor” features exclusive Nikon technologies and outstanding precision.

First of all, since it is an RGB sensor, it can measure color information as well as light intensity. Exposure should change according to color conditions, even when brightness remains constant. For example, reddish evening light and cloudy daylight could have the same brightness. So if the camera calculates exposure only by measuring light intensity, optimal exposure for both situations will be identical. The RGB sensor distinguishes scenes according to their colors, so true optimal exposure can be calculated for each situation. Among all film cameras, only Nikon film cameras have used this technology. A second advantage is the number of pixels, 1,005, which is far more pixels than any other camera maker's camera offers. The more pixels, the more detailed the subject information is for the camera to take advantage of. As a result, Nikon offers more precise exposure control.

I see. So the “1,005-pixel RGB sensor” achieves such high precision by measuring as many elements as possible, including information on colors and detail.

Exactly. But to handle this larger volume of information, a camera must have larger CPU capacity, so we always have to consider that balance. Increasing information for exposure control could mean sacrificing other information, so ultimately, we cannot simply use more and more pixels to create better images. Considering the need to balance camera functions overall, I can say that a 1,005-pixel count is ideal for the metering sensor.

Optimal exposure is a matter of personal preference.
In shooting, the highest priority should be to reproduce an impression faithfully.

Nikon reportedly uses a gigantic collection of shooting data to design an algorithm for metering. Could you give us details about this development process?

Superior Nikon camera precision relies on a gigantic collection of shooting data for realizing optimal exposure under all shooting conditions.

After we consider the various types of scenes that various customers shoot, we go ahead and take pictures of such scenes ourselves. Then, we set the exposure value that is optimal for each situation using the shooting data. Specifically, at this stage, we select the best images among pictures shot using various exposure values. In repeating this process for approximate scenes shot, we collect a lot of data for building a database that could serve as a basis for metering algorithm design. Then we devise a trial system, install it on the camera, and take pictures again. The team examines these pictures from the perspective of approximating overall camera performance, considering aspects of marketing such as which shooting situations should be emphasized, as fine tuning continues. We certainly put a great deal of emphasis on actual shooting data throughout this process of development.

How many pictures are included in your database?

We continually update the database, which has more than scores of thousands of pictures. But normally, in the development process, we use information regarding important shooting situations, depending on camera concept, so we cannot specify how many pictures go into development. As another reference, we repeated trial shooting for two years in developing our 1,005-pixel RGB sensor, in order to accommodate as many prospective shooting situations as possible. The angle of the sun's rays differs from region to region, so, to build up our database, we have to go to various regions, from north to south, to take pictures. We also try to include situations featuring as much variety as possible, referring to information from Nikon offices around the world. This requires shooting under harsh conditions, such as those on snow-covered mountains, so it takes physical strength to complete our assignments.

I see.

But at the same time, we have to recognize that it is impossible to account for all the shooting situations that our many customers are interested in shooting. Furthermore, impressions or preferences of brightness differ from person to person, so if we were to stick too closely to particular exposure values that we think are perfect for specific situations, situations would arise in which such rigid exposure values provided by the camera would produce disappointing results. In developing the Matrix Metering System, we repeatedly discussed whether the exposure settings should be for images to “look attractive” or to be “faithful to a photographer's impressions upon shooting.” Finally, in order to minimize the likelihood of producing disappointing results, we decided that exposure should produce images that are “faithful to a photographer's impressions upon shooting.”

The choice to emphasize images that are “faithful to a photographer's impressions upon shooting” seems characteristic of Nikon's approach to photography.

I agree. Also, an advantage of this concept is that it makes it easier for customers to make adjustments which they prefer. A user gains the capability to add a unique touch of brightness, for instance. We aim to give photographers more flexibility to shoot without extreme exposure compensation, so that they can capture the backlight of a bright scene or the shadowiness of a dark scene in images, just as they like.