In addition to focusing the camera, pressing the shutter button half way down also...

• A. Focuses the camera
• B. Zooms the lens
• C. Changes white balance
• D. Measures the light

Answer: (D)

When you press the shutter button halfway, the camera starts preparing for the shot by doing two things: it engages autofocus so the scene can be sharply focused, and it activates exposure metering to evaluate the brightness of the scene. That metering is how the camera determines the proper exposure settings (like shutter speed and aperture) to avoid under- or overexposure. Zooming the lens isn’t triggered by a half-press—that’s done by separate lens controls or camera zoom motors. White balance adjustments also aren’t moved by a half-press; WB is set in the camera’s settings or can be adjusted separately. So, the half-press primarily measures the light to help set the right exposure.