In photographic terms, ‘aperture’ typically refers to the size of the opening in the lens (which allows the transfer of light to the sensor/film). In general use, ‘aperture’ is just a fancy word for ‘opening’ or ‘hole’.

A lens’ aperture is one of the most central choices a photographer makes, as the size of the aperture (also referred to as f-stop) has sweeping consequences for the resulting shot:

  • A bigger aperture (lower f-number or f-stop) lets more light pass through the lens, thus allowing for faster shutter speeds (allowing the stopping of motion) or lower sensitivity (leading to lower noise).
  • A bigger aperture makes the depth-of-field narrower, thus allowing for stronger subject separation.

Furthermore, either extremes of a lens’ aperture range typically cause negative effects on image quality: when the aperture is at its largest, this typically causes a loss of sharpness and contrast and light fall-off in frame corners (a.k.a vignetting), as well as accentuation of various aberrations; on the other hand, when the aperture is at its smallest (typically, past f/11), this increases the loss of sharpness and contrast due to diffraction. Hence, when considering only a lens’ ability to resolve detail, most lenses have a ‘sweet spot’ between the extremes of the lens’ aperture range.

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