Metering the light
The camera will try to give you a correct exposure automatically. However, some basic understanding of the light metering modes are needed. Two general modes of light metering are available on the 9000:
- Center-weighted average metering
- Spot metering
Those two modes are settable with the light metering selector, located at the far left of the camera. It has actually four modes: Average, Spot, H and S. Ignore the H and S modes for now; they are special spot meter settings, and we will look at them later in the section "Advanced concepts -- Metering the light part II".
Center-weighted average metering
This mode should be used for general photography. It looks at the whole scene through the lens and computes an average value for exposure, treating the center of the picture as the most important part. In most cases it will do an adequate job, but in some cases it will fail. Typical cases where it will underexpose the main subject are when the subject is backlit, or scenes where strong point light sources exists in the picture (e.g. the sun). Typical cases where it will where it will overexpose the main subject is when the main subject has a dark background. How to get around these cases?
Spot metering
Enter spot metering. Look through the viewfinder -- in the middle, there is one small rectangle and one larger circle surrounding it. The rectangle is the location of the autofocus sensor and does not concern exposure. Inside the circle (including the rectangle) is where the camera will take a reading when spot metering is set. You can now meter on the most important part in the scene! But what if the most important part of the scene isn't in the middle?
The AEL button
AEL means Auto Exposure Lock. With this handy little button, located right under your right thumb when you hold the camera normally, you can lock the exposure. Point the circle to the thing you want to have correctly exposed -- for example a face. Press the AEL button. While pressing, recompose and release the shutter. The camera will expose with regards to what is in the spot metering circle, and not care about anything else in the scene.
The AEL button can also be used with center-weighted average metering for locking exposure and recomposing in tricky situations.
- If you release the AEL button, the exposure will no longer be locked, and you will have to lock it again.
- If you forget to press the AEL button and lock the exposure on the main subject while in spot metering mode, the resulting exposure will be totally unpredictable, as spot metering just checks what is currently in the very center of the scene.
- Spot metering does not work with flash. Flash exposure is center-weighted average regardless of the setting of the light metering mode switch.
- The metering systems are calibrated to treat 18% gray as "normal exposure". You need to have this is mind especially when using spot metering; if you spot meter on a dark subject, the image will be overexposed, while metering a light subject will lead to underexposure. More information is in "Metering the light part II".
