Lens Speed Savvy

Lens speed is sometimes called an aperture or f-stop

This number indicates how much light the lens transmits. An aperture is an opening. The larger the aperture, the more light goes through it, whether we're dealing with a window or a camera lens. All things being equal, a larger opening will let you shoot at a higher shutter speed, thus stopping action and reducing camera shake. A smaller aperture will provide a greater range of sharpness (depth of field) in your photograph but require a slower shutter speed. ✓

Gulls photographed using 1.8mm lens

A lens is often referred to as being a "fast" or "slow" lens depending on its largest aperture compared to the speed of other lenses having similar focal lengths engineered for a similar format. Lens speed is provided by it's smallest f-number, or as an alternative it's maximum aperture opening or largest numerical aperture, is the way to compare analogous lenses.

Lens speed is significant when capturing images in poor light, or when using long telephoto lenses. For manipulating depth of field, particularly with portrait photography, the speed of a lens is a primary variable when combed with other variables like camera format size and focal length.

Lenses will typically be labeled as being "slower" or "faster" over another lens using this same process. A lens having a f/4.0 maximum aperture is faster than a lens having a f/6.3 aperture, although neither lens is all that fast. A lens containing an f/2.8 aperture is not as fast as a lens containing an f/1.8,aperture, although both lenses are considered fast.

The lens ranges thought to be "fast" has changed to smaller f-numbers during the past several years, because of advances in lens layout, optical construction, plus glass and optical coating quality. For instance, the Encyclopedia Britannica of 1911 reports that "...[Lenses] are also sometimes classified according to their rapidity, as expressed by their effective apertures, into extra rapid, with apertures larger than f/6; rapid, with apertures from f/6 to f/8; slow, with apertures less than f/11." (Here, interpretation of "apertures less than f/11" requires literal interpretation as aperture diameters less than focal length divided by 11, equivalent to saying "f-numbers greater than 11.")

On 35mm cameras, the fastest lens designs are most often within the "standard lens" range hovering around 50 mm. Longer telephoto lenses with wide-angle retro focus layouts having a tendency of being slower. Also, "prime" (with fixed focal lengths) lenses are typically faster than zoom design lenses.

Lens speed is most often related to the price or lens quality. This is true as lenses having maximum apertures which are larger require more effort to design, more precision to manufacture, require special coatings and better glass quality. Although this is not cast in concrete rule, however, as several fast high-quality lenses are available which are relatively reasonably priced, particularly within the normal focal length lenses.

Fast lenses

Several of the fastest camera lenses ever manufactured are:
  • Carl Zeiss 50mm f/0.7 (A lens with limited production built for the NASA space program, and used with 35mm movie cameras by Stanley Kubrick for some Barry Lyndon candlelit scenes )
  • Canon 50mm f/0.95 (Available in TV and Canon 7 Rangefinder Version)
  • Canon EF 50mm f/1.0 (for Canon autofocus SLR, no longer being produced)
  • Leica Noctilux-M 50 mm f/0.95 ASPH, released on September 15, 2008, it is the fastest Aspherical lens to have ever gone into mass production.
  • Leica Noctilux 50mm f/1.0 (Leica M mount, discontinued and replaced in 2008 with the new Noctilux listed above
  • Nikon TV-Nikkor 35mm f/0.9-Fastest Nikon lens ever built.
  • Tokyo Kogaku Toko 5cm f/0.7 (WWII) and Simlar 5cm f/0.7 (1951, only three were manufactured, of which two were used in an expidition to the South pole)
  • Rodenstock TV-Heligon 50mm f/0.75
  • Schneider Kreuznach 50mm f/0.95 'Xenon' (manufactured in a C mount)

updated article Nov 9, 2011

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