Lens speed


Lens speed is the maximum aperture diameter, or minimum f-number, of a photographic lens. A lens with a larger than average maximum aperture 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 is "slow" because it delivers less light intensity and requires a slower 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, as well as for sports photography and photojournalism.
Lenses may also be referred to as being "faster" or "slower" than one another; so an 3.5 lens can be described as faster than an 5.6 despite 3.5 not generally being considered "fast" outright. What is considered fast largely depends on focal length, image diameter, and in the case of zoom lenses, zoom factor.

Tradeoffs

Attaining maximum lens speed requires engineering tradeoffs, and as such, "prime" lenses are generally faster than zoom lenses.
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 1.8 II or Nikon AF Nikkor 50mm 1.8D are very inexpensive, but quite fast and optically well-regarded. Old fast manual focus lenses, such as the Nikkor-S or Nikkor AI-S 50mm 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 1.2 lens to produce 0.74.

Fast lenses

While the fastest lenses in general production in the 2010s were 1.2 or 1.4, the 2020s have seen several 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 "... are also sometimes classified according to their rapidity, as expressed by their effective apertures, into extra rapid, with apertures larger than 6; rapid, with apertures from 6 to 8; slow, with apertures less than 11" whilst today, 6 would be deemed at the rather slow end.
Image:Canon 85mm comparison.jpg|thumb|250px|Canon 85mm 1.8 and 1.2 showing their large entrance pupils
For scale, note that 0.5, 0.7, 1.0, 1.4, and 2.0 are each 1 f-stop apart, as an f-stop corresponds to a factor of the square root of 2, about 1.4. Thus around 1.0, a change of 0.1 corresponds to about 1/4 of an f-stop : 1.0 is about 50% faster than 1.2, which is about 50% faster than 1.4.
, Canon, Nikon, Pentax and Sony all make an autofocus 50mm 1.4 lens. These are not unusual lenses and are relatively inexpensive. As of 2023, Canon also makes autofocus 50mm and 85mm 1.2 lenses, while Nikon makes a manual focus 58mm 0.95 lens and autofocus 50 and 85mm 1.2 lenses; see Canon EF 50mm lenses and Canon EF 85mm lenses for details. Pentax makes a 50mm 1.4 lens and 55mm 1.4 lens for APS-C cameras; see Pentax lenses. Sony makes several 50mm 1.4 lenses as well as a 50mm 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, 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. In 1966, in response to the trend, Carl Zeiss displayed a prop lens christened the Super-Q-Gigantar 40mm 0.33 at photokina. Made from various parts found around the factory, the claimed speed and focal lengths were purely nominal and it wasn't usable for photography.

Maximum possible speed

Theoretically, the smallest f-number is 0, corresponding to a lens with an infinite entrance pupil diameter. In practice, that cannot be reached due to mechanical constraints of the camera system. Even for systems that can be designed without significant constraints on lens size and image plane distance, the cost of going beyond a numerical aperture of 0.95 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 1.0 to 1.2, with rather strong vignetting towards the edges of the image. Flange distances are significantly smaller for rangefinder and mirrorless cameras, theoretically enabling designs down to something like f/0.7 or even faster. The chance of seeing such lenses designed for use with 35mm 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 were as follows:
  • Cosina Voigtländer Super Nokton 29mm 0.8 Micro Four Thirds mount
  • Cosina Voigtländer Nokton 10.5mm, 17.5mm, 25mm, 42.5mm, 60mm 0.95 for Micro Four Thirds mount
  • Vantage One T1.0 Cine lenses from 17.5mm to 120mm
  • SLR Magic 25mm T/0.95
  • SLR Magic 35mm T/0.95
  • Laowa 18mm, 25mm, 33mm 0.95 For Super35mm Frame sensor
  • Laowa 28mm, 35mm, 45mm 0.95 For Full Frame sensor
  • Handevision Ibelux 40mm 0.85
  • Fujinon 43mm 0.85 VRF43LMD
  • Leica Noctilux-M 50mm 0.95 ASPH.
  • Zhongyi Mitakon 50mm and 35mm 0.95 in various optical versions and mounts, of which at least the 50mm for Leica M rangefinders has been found to in fact only be 1.06!
  • Nikon Noct-Nikkor Z 58mm 0.95
The following lenses are no longer in production :
  • American Optical 81mm 3.259" 0.38 Solid Schmidt Mirror lens
  • GOI CV 20mm 0.5 Mirror lens
  • Zeiss Planar 50mm 0.7
  • Tokyo Kogaku Similar 50mm 0.7
  • Kinoptik Lynxar 60mm 0.7
  • Wray 64mm 0.71
  • LOMO 60mm 0.75
  • Aerojet Delft Rayxar 105mm 0.75 Full Frame aerial photography lens
  • Aerojet Delft Rayxar 150mm 0.75 Medium Format aerial photography lens
  • Aerojet Delft Rayxar 250mm 0.75 Large Format aerial photography lens
  • Baker-Nunn camera 500mm 0.75 twelve used for tracking satellites
  • American Optical 43mm 1.715" 0.8
  • JML Optical 64mm 0.85
  • Leica Summar 75mm 0.85 Reproduction lens, not for photography.
  • Leica Leitz-IR 150mm 0.85 Reproduction lens, not for photography.
  • Farrand Super Farron 76mm 0.87
  • Farrand Super Farron 150mm 0.87 Medium Format aerial photography lens
  • Canon 50mm 0.95
  • Kiev Рекорд-4 52mm 0.9
  • Nikon TV-Nikkor 35mm 0.9
  • Noktor 50mm 0.95
  • SLR Magic HyperPrime CINE and LM 50mm 0.92 T0.95
  • Astro Berlin 52mm 0.95
  • Leitz Perkin Elmer 4.5" 114mm 0.95 T1
  • Pacific Optical 25mm 1.0
  • Leica Noctilux-M 50mm 1.0
  • Canon EF 50mm 1.0 L USM
  • Panavision 50mm 1.0
  • Nikkor-O 50mm 1.0 Prototype lens for Nikkor-S Rangefinder camera
  • Leica ELCAN 90mm 1.0
  • Wild Heerbrugg Reconar 98mm 1.0 Medium Format aerial photography lens
  • Kollmorgen 153mm 1.0
  • Zeiss UR 250mm 1.0
  • Canon 8.5–25.5mm 1.0 zoom lens
Apart from those already mentioned, many very fast lenses exist in C-mount, including:
  • Fujinon 50mm 0.7
  • Panasonic 6mm f0.75
  • Canon 'TV-16' 25mm 0.78
  • Computar 8mm 0.8
  • VS Technology 25mm 0.85
  • VS Technology 50mm 0.85
  • Apollo 25mm 0.85
  • Ernitec 25mm 0.85
  • Fujinon 25mm 0.85
  • Tarcus 25mm 0.85
  • Kern Switar 18mm 0.9
  • Fujinon YV2.7x2.9LR4A-SA 2.9-8mm 0.95
  • Ampex 'LE610 Television Lens' 25mm 0.95
  • Angénieux 25mm 0.95 Type 'M1' and 'M2'
  • Angénieux 28mm 0.95 Type 'M1' and 'M2'
  • Angénieux 35mm 0.95
  • Angénieux 50mm 0.95 Type 'M1' and 'M2'
  • AstroScope 25mm 0.95
  • Avenir 25mm 0.95
  • Century 'Nighthawk' 25mm 0.95
  • Carl Meyer 25mm 0.95
  • Cinetar 25mm 0.95
  • Goyo Optical 17mm, 25mm, and 50mm 0.95
  • JML 25mm and 50mm 0.95
  • Navitar 25mm and 50mm 0.95
  • Navitron 25mm and 50mm 0.95
  • Schneider Kreuznach 'Xenon' 17mm, 25mm, and 50mm 0.95
  • Senko 25mm and 50mm 0.95
  • Soligor 'Super Elitar' 25mm 0.95
  • Som Berthiot 'Cinor' 25mm and 50mm 0.95
  • Tarcus 'I.T.V. Lens' 50mm 0.95
  • Precise Optics 50mm 0.95
  • Kowa 50mm 0.95
  • Yakumo 25mm and 50mm 0.95
  • Zeika 'Nominar' 25mm 0.95
  • Kaligar 'Nominar' 25mm 0.95
  • Dallmeyer 25mm 0.99
  • Astro Berlin 25mm 1.0
  • Bausch & Lomb 29mm 1.0
  • Astro Berlin 'Tachonar' 35mm and 75mm 1.0
  • Carl Meyer Videostigmat 1.5" 38mm 1.0
  • RTH Monital 130mm 1.0 made by SOPELEM in France, Super35mm cine lens
Very fast lenses in D-mount for use in 8mm film and video 8 cameras:
  • Kern Switar 13mm 0.9
  • Cinetor 'TELE-PHOTO' 37.5mm 1.0
  • Walz 'TELEPHOTO' 37.5mm 1.0
  • Amitar 'Telephoto' 38.1mm 1.0
  • Rexer 'TELE' 38mm 1.0
  • Manon 'Telephoto' 37.5mm 1.0
Very fast lenses used in X-ray machines:
  • Canon X 60mm 0.7
  • Canon X 100mm 0.7
  • Zeiss R-Biotar 100mm 0.73
  • LOMO 100mm 0.73
  • Canon 50mm and 65mm 0.75
  • Leitz 50mm and 65mm 0.75
  • Astro-Berlin Tachon 65mm 0.75
  • De Oude Delft Rayxar 50mm, 65mm and 105mm, and allegedly 150mm 0.75
  • De Oude Delft Rayxar 90mm 1.0
  • Rodenstock XR-Heligon 42mm and 50mm 0.75
  • Rodenstock XR-Heligon 68mm f/1
  • Kowa 42mm and 65mm 0.75
  • Carl Zeiss Jena 50mm 0.77
  • Kowa 55mm 0.8
  • Zeiss R-Biotar 125mm 0.8
  • Zeiss R-Biotar 55mm 0.85
  • Lenzar Optics 184.6mm 0.9
  • Kowa 33.5mm 0.95
  • Kowa 55mm 1.0
  • Rodenstock Heligon 68mm 1.0
  • Canon 65mm and 90mm 1.0
  • Fuji 90mm 1.0
  • Kowa 90mm 1.0