The Alpha has three different schemes for evaluating the light received by its exposure sensors. You can choose among them by pressing the Fn button and choosing Metering Mode from the screen that pops up (see Figure 4.7).
Figure 4.7 Choose a metering mode here.
Multi segment. The Alpha SLT-A77 has an advantage over many earlier models because of its unique internal structure. The translucent mirror allows light to reach the image sensor constantly, so the camera uses the entire image sensor to evaluate the exposure of your shots. So, instead of the more usual 40 or 49 metering zones, the SLT models use the whole sensor surface, which is considered to consist of 1,200 separate zones, as shown in Figure 4.8. The camera evaluates the measurements to make an educated guess about what kind of picture you’re taking, based on examination of exposure data derived from thousands of different real-world photos. For example, if the top sections of a picture are much lighter than the bottom portions, the algorithm can assume that the scene is a landscape photo with lots of sky. This mode is the best all-purpose metering method for most pictures, like the typical scene in
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