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Lens Speed

Lens speed (f), indicates how much light the lens is capable of shooting to render the subject. It is the ratio of the diameter of the aperture input and focal length.

The following apply when setting the lens speed:

  • Brighter lens luminosity, produces better quality rendering of the resulting images.
  • Higher f-numbers indicate smaller apertures, shorter exposure times, and a lower risk of blurred images.
  • When increasing the focal length, decrease the lens speed.
  • Lowering the lens speed and exposure time under good light conditions, achieves less depth of field.

Methods of expressing luminosity

  • F-number: f4 or ranges in Zoom Lenses: F4.0-5.6
  • Evaluative number: f1/4 or ranges in Zoom Lenses: f1/4.0-5.6

Quality maximum aperture lenses

  • f1.4 for lenses with fixed focal lengths
  • f2.8 for zoom lenses with variable focal lengths

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