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The Nikon D300s has three metering pattern options that will be familiar if you have used a Nikon AF camera before: Matrix, center-weighted, and spot. To select a metering mode, rotate the metering mode dial, which is set around the AE-L/AF-L button to the right of the viewfinder eyepiece. The appropriate icon will be displayed in the control panel display.

Matrix metering: The pattern for this mode covers virtually the entire frame area with each of the 1005 segments on the RGB metering sensor (located in the viewfinder head of the camera), acting as a sampling point. This long-established sensor (first used in the Nikon F5 camera) has been enhanced by the addition of a small diffraction grating placed immediately in front of it. This separates the light falling on the sensor into its component colors to improve the efficiency and accuracy with which it assesses both the nature and the color of the light from the scene being photographed; it is the core of the Scene Recognition System that assesses the distribution of color within the frame and uses this information to improve metering accuracy, especially for skin tones.

To derive the most from the Matrix metering capabilities of the D300s, it is necessary to use a D- or G-type Nikkor lens, since these provide additional focus distance information that assists the camera in estimating the distance from camera to subject. The metering system also knows which AF point is selected and uses this information to estimate the position of the subject within the frame. Nikon calls this system 3D Color Matrix metering II. If an AF Nikkor lens that does not communicate distance information to the camera is used, the system simply defaults to standard Color Matrix metering II (i.e., the distance information is not integrated in the exposure computations). This also applies to the use of a non-CPU type lens, provided the focal length and maximum aperture value are specified using the Non-CPU lens data item in the Setup menu.

In the three automated exposure modes, the Matrix metering (and i-TTL flash control) also benefits from the enhanced analysis of highlights within the frame performed by the Scene Recognition System feature. By assessing color as well as brightness and contrast, then comparing the results against a database of over 60,000 sample images that cover an enormous range of lighting conditions, the D300s offers the most advanced TTL metering available in a Nikon camera to date. Matrix metering uses four principal factors when calculating an exposure value:

• The overall brightness level in the scene

• The ratio of brightness between the 1005 segments

• The focused distance, provided by the lens (D- or G-type only)

• The location of the active AF point

Center-weighted metering: The center-weighted metering pattern harks back to the TTL metering systems used by early Nikon SLR film cameras. In these cameras the frame area was usually divided in a 60:40 ratio with the bias placed on the central portion of the frame. The D300s uses a higher ratio of 75:25, with 75% of the exposure reading based on the central circular area of the frame and the remaining 25% based on the outer area (it is also possible to select an option that averages the entire frame area, via CS-b5). Unlike Matrix metering, no color information is assessed when the center-weighted pattern is selected, so metering is performed using a grayscale.

Spot metering: Spot metering is extremely useful for metering from a highly specific area of a scene. For example, faced with a subject against a virtually black background, which might cause the Matrix metering system to overexpose the subject, the spot meter allows you to take a reading from the subject without it being influenced by the background. The sensing area for the spot-metering pattern is a circle, approximately 0.12 inch (3 mm) in diameter, which represents about 2% of the total frame area. This circle is centered on the active AF point, unless Auto-area AF is selected or a non-CPU lens is used, in which case, the central AF point is the only area to perform metering. Again, as with the center-weighted pattern, no color information is assessed when the spot-metering pattern is selected, so metering is performed using a grayscale.