The adjustable opening or f-stop of a lens determines how much light passes through the lens on its way to the film plane, or nowadays, to the surface of the camera's imaging sensor. Faster lenses have wider apertures, which in turn allow for faster shutter speeds.
This is the opening in your lens that allows light through. It’s also known as f-stops. A maximum aperture (widest) might be f/1.4 or f/2.8. And the minimum aperture (smallest opening) might be f/22.
Aperture directly influences depth of field. This means that f/2.8 gives you a shallow depth of field (least amount of the scene in focus). And f/22 gives you a deep depth of field (everything is in focus).
The wider the aperture is set, the shallower the depth of field will be in the resulting image. Wider apertures allow for selective focus, the ability to isolate your subject from background and foreground elements within the frame. Conversely, if you stop the lens aperture down to its smallest openings, you increase the depth of field, or the amount of focus from foreground to background. Generally speaking, most lenses display the highest level of resolving power when set to about three stops down from the widest aperture. The term "highest level of resolving power" does not mean the greatest level of depth of field. It just means what is in focus cannot be rendered any sharper by that particular lens, regardless of the image's depth of field.
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