© 2007 Wazari Wazir | Raptor Watch | Tanjung Tuan Malacca Lens speed refers to the maximum aperture diameter, or minimum f-number, of a photographic lens. A lens with a larger maximum aperture (that is, a smaller minimum f-number) is a fast lens because it delivers more light intensity (illuminance) to the focal plane, allowing a faster shutter speed. A smaller maximum aperture (larger minimum f-number) is “slow” because it delivers less light intensity and requires a slower shutter speed. A lens may be referred to as “fast” or “slow” depending on its maximum aperture compared to other lenses of similar focal length designed for a similar film format. Lens speed given by the minimum f-number, or alternatively maximum aperture diameter or maximum numerical aperture,…