The aperture of the lens controls the amount of light that passes through on its way to the camera's sensor or film plane. A camera's aperture is also commonly called its f-stop, though 'f-stop' technically refers to the diameter of the opening created by internal adjustable blades, rather than the entire mechanism.
Zoom lenses have become increasingly popular over the years for a number of reasons, including convenience (less lost time swapping lenses and in turn less chance of getting dust on the camera sensor and/or missing the shot altogether), weight (one slightlier heavier zoom can replace two or three slightly lighter but collectively heavier lenses) and slimmer camera bags (have you flown with carry-on baggage lately?).
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