A fast prime (fixed focal length) lens, the Canon 50mm f/1.4 (left), and a slower zoom lens, the Canon 18–55mm f/3.5–5.6 (right); this lens is faster at 18mm than it is at 55mm.

Lens speed is the maximum aperture diameter, or minimum f-number, of a photographic lens. A lens with a larger than average maximum aperture (that is, a smaller minimum f-number) is called a "fast lens" because it can achieve the same exposure as an average lens with a faster shutter speed. Conversely, a smaller maximum aperture (larger minimum f-number) is "slow" because it delivers less light intensity and requires a slower (longer) shutter speed.

A fast lens speed is desirable in taking pictures in dim light, for stability with long telephoto lenses, and for controlling depth of field and bokeh, especially in portrait photography,[1] as well as for sports photography and photojournalism.

Lenses may also be referred to as being "faster" or "slower" than one another; so an f/3.5 lens can be described as faster than an f/5.6 despite f/3.5 not generally being considered "fast" outright. What is considered fast largely depends on focal length, image diameter (i.e. format covered, such as APS, full frame, medium format), and in the case of zoom lenses, zoom factor.

Tradeoffs

Three 50 mm prime lenses from Minolta with lens speed 3.5 (a macro photography lens, speed of less priority), 1.7 (standard), and 1.2 (large opening and high speed, typically expensive), showing the relation between entry lens diameter and lens speed.

Attaining maximum lens speed requires engineering tradeoffs, and as such, "prime" (fixed focal length) lenses are generally faster than zoom lenses.[2]

With 35mm film cameras and full-frame digital cameras, the fastest lenses are typically in the "normal lens" range near 50mm; here, there are several relatively inexpensive high-quality fast lenses available. For example, the Canon EF 50mm f/1.8 II or Nikon AF Nikkor 50mm f/1.8D are very inexpensive, but quite fast and optically well-regarded. Old fast manual focus lenses, such as the Nikkor-S(C) or Nikkor AI-S 50mm f/1.4, or Canon's FD and M39 counterparts, were historically produced abundantly, and are thus sold relatively inexpensively on the used lens market.

Especially outside of the "normal" focal length, lens speed also tends to correlate with the price and/or quality of the lens. This is because lenses with larger maximum apertures require greater care with regard to design, precision of manufacture, special coatings and quality of glass. At wide apertures, spherical aberration becomes more significant and must be corrected. Thus, faster telephoto and wide-angle retrofocus designs tend to be much more expensive.

A telecompressor, also known as a speed booster, may be used to increase the speed of a lens with a corresponding reduction to its focal length. For example, the Metabones 0.58x BMPCC speed booster may be combined with a f/1.2 lens to produce f/0.74.[3]

Fast lenses

While the fastest lenses in general production in the 2010s were f/1.2 or f/1.4, the 2020s have seen several f/0.95 lenses, see below.

What is considered "fast" has evolved to lower f-numbers over the years, due to advances in lens design, optical manufacturing, quality of glass, optical coatings, and the move toward smaller imaging formats. For example, the 1911 Encyclopædia Britannica states 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" whilst today, f/6 would be deemed at the rather slow end.

Canon 85mm f/1.8 and f/1.2 showing their large entrance pupils

For scale, note that f/0.5, f/0.7, f/1.0, f/1.4, and f/2.0 are each 1 f-stop apart (2× as fast), as an f-stop corresponds to a factor of the square root of 2, about 1.4. Thus around f/1.0, a change of 0.1 corresponds to about 1/4 of an f-stop (by linear approximation): f/1.0 is about 50% faster than f/1.2, which is about 50% faster than f/1.4.

As of 2017, Canon, Nikon, Pentax and Sony all make an autofocus 50mm f/1.4 lens. These are not unusual lenses and are relatively inexpensive. As of 2023, Canon also makes autofocus 50mm and 85mm f/1.2 lenses, while Nikon makes a manual focus 58mm f/0.95 lens and autofocus 50 and 85mm f/1.2 lenses; see Canon EF 50mm lenses and Canon EF 85mm lenses for details. Pentax makes a 50mm f/1.4 lens and 55mm f/1.4 lens for APS-C cameras; see Pentax lenses. Sony makes several 50mm f/1.4 lenses as well as a 50mm f/1.2.

The maximum exposure time for hand-held photography can be increased with an image stabilisation system. In 2014, Panasonic introduced the fastest lens with in-built stabilisation, the Leica Nocticron 42.5 mm f/1.2, which can even be operated with dual image stabilisation (Dual I.S.), provided that the camera body has an additional stabilising system at the image sensor.

In the mid 1960s, there was something of a fad for fast lenses among the major manufacturers.[4] In 1966, in response to the trend, Carl Zeiss displayed a prop lens christened the Super-Q-Gigantar 40mm f/0.33 at photokina.[4] Made from various parts found around the factory (the lenses came from a darkroom condenser enlarger), the claimed speed and focal lengths were purely nominal and it wasn't usable for photography.[4][5]

Maximum possible speed

Theoretically, the smallest f-number is 0 (or numerical aperture of 1), corresponding to a lens with an infinite entrance pupil diameter. In practice, that cannot be reached due to mechanical constraints of the camera system (shutter clearance, mount diameter). Even for systems that can be designed without significant constraints on lens size and image plane distance (e.g. microscopy and photolithography systems), the cost of going beyond a numerical aperture of 0.95 (f/0.164) is usually prohibitive.

In SLR camera systems, typical mount diameters are in the range of 44–54 mm, with flange distances around 45 mm. This limits the maximum possible f-number to f/1.0 to f/1.2, with rather strong vignetting towards the edges of the image. Flange distances are significantly smaller for rangefinder and mirrorless cameras (even below 20 mm), theoretically enabling designs down to something like f/0.7 or even faster. The chance of seeing such lenses designed for use with 35mm ("full-frame") cameras, digital or film, in practice will be slim, since their cost and weight are likely not competitive with respect to equivalent imaging solutions employing larger sensors.

List of ultrafast lenses

Some of the fastest camera lenses in production as of 2021 were as follows:

Cosina Voigtländer Super Nokton 29 mm / 0.8

The following lenses are no longer in production as of 2021:

Apart from those already mentioned, many very fast lenses exist in C-mount (as used by 16mm film cameras, CCTV, medical & scientific imaging systems), including:

Very fast lenses in D-mount for use in (Super-)8mm film and video (Hi)8 cameras:

Very fast lenses used in X-ray machines:

References

  1. ^ Waldren, Margaret (and others) Advanced Digital Photography 2004 Media Publishing
  2. ^ Long, Ben Complete Digital Photography 2004 Charles River Media
  3. ^ "F0.74 - new Metabones Speed Boosters break boundaries - EOSHD". EOSHD. 2 December 2013. Retrieved 2015-11-19.
  4. ^ a b c Maiello, Agostino (January 2000). "L'OBIETTIVO PIU' LUMINOSO DEL MONDO". Nadir.it (in Italian). Nadir Magazine. Retrieved 28 September 2013.
  5. ^ Zhang, Michael (August 6, 2013). "Carl Zeiss Super-Q-Gigantar 40mm f/0.33: The Fastest Lens Ever Made?". Petapixel. Retrieved 28 September 2013.
  6. ^ "Cosina Voigtänder - Nokton 25mm F0.95". Cosina Voigtländer. 2010-08-26. Archived from the original on 2013-12-12. Retrieved 2013-12-03.
  7. ^ "29 mm / 1:0,8 Super Nokton asphärisch | Voigtländer". www.voigtlaender.de.
  8. ^ "MFT- Mount | Voigtländer". www.voigtlaender.de.
  9. ^ "Leica offers World's fastest Aspherical lens". Leica Camera. 2008-09-15. Retrieved 2009-02-14.
  10. ^ photonstophotos.net. 8 May 2022 https://photonstophotos.net/GeneralTopics/Lenses/OpticalBench/OpticalBench.htm#Data/CN111965793_Example01P.txt,figureOpacity=0.25,AxisO,OffAxis. ((cite web)): Missing or empty |title= (help)
  11. ^ "USAF Lens Datasheets - Type 1 Aerial Reconnaissance". archive.org. Retrieved 4 October 2013.
  12. ^ "Signal Corps Engineering Laboratories 33mm f/0.6 Lens - Nov 19, 2011 | Fuller's LLC in PA".
  13. ^ "Fujinon-IDEAX 125mm f0.67 (f0.85?)". forum.mflenses.com.
  14. ^ Two Special Lenses for "Barry Lyndon", by Ed DiGiulio (President, Cinema Products Corp.), American Cinematographer
  15. ^ Volosov, David (1978). Fotograficheskaya optika.
  16. ^ "TV-Nikkor 35mm F0.9 Big First Super Light". Archived from the original on June 30, 2013. Retrieved 2016-05-14.
  17. ^ Lossau, Jürgen (2003). The Complete Catalogue Of Movie Cameras, Hamburg/Germany, atoll medien, p. 59, ISBN 3-9807235-3-4
  18. ^ Brandenberger, Arthur (1961). "The Use of Baker-Nunn Cameras for Tracking of Artificial Earth Satellites" (PDF). American Society for Photogrammetry and Remote Sensing (ASPRS). 28th Annual Meeting: 9.
  19. ^ "Science, Kern-Paillard advertisement". 165. ((cite journal)): Cite journal requires |journal= (help)
  20. ^ "Carl Meyer Videostigmat f1.0 1.5" (38mm)". forum.mflenses.com.
  21. ^ "Rodenstock XR-heligon 68mm F1.0 M42 mount".

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