 | |
| Introduced in |
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|---|---|
| Author | Alvan Graham Clark,Paul Rudolph, andHorace William Lee |
| Construction | 4–6 elements in 4+ groups |
Thedouble Gauss lens is acompound lens used mostly incamera lenses that reducesoptical aberrations over a largefocal plane.
The earliest double Gauss lens, patented byAlvan Graham Clark in 1888, consists of two symmetrically-arrangedGauss lenses. Each Gauss lens is a two-elementachromatic lens with a positivemeniscus lens on the object side and a negative meniscus lens on the image side. In Clark's symmetric arrangement, this makes four elements in four groups: two positive meniscus lenses on the outside with two negative meniscus lenses inside them. The symmetry of the system and the splitting of the optical power into many elements reduces theoptical aberrations within the system.
There are many variations of the design. Sometimes extra lens elements are added. The basic lens type is one of the most developed and used photographic lenses. The design forms the basis for many camera lenses in use today, especially the wide-aperturestandard lenses used with 35 mm and other small-format cameras. It can offer good results up tof/1.4 with a widefield of view, usually with seven elements for extra aberration control. Modern super wide aperture models off/1.0 can have eight or more elements, while more moderate aperturef/2.8 versions can be simplified to five elements.
The Double Gauss was likely the most intensively studiedlens formula of the twentieth century,[1]: 245 producing dozens of major variants, scores of minor variants, hundreds of marketed lenses and tens of millions of unit sales.[1]: 444–452 [2]: 123–128 It has few flaws, most notably a small amount of obliquespherical aberration, which could lower peripheral contrast.[1]: 245–248 Double Gauss/Planar tweaks formed the basis for most normal and near-normalprime lens designs with wide apertures for sixty years.
The original two elementGauss was a telescopeobjective lens consisting of closely spaced positive and negative menisci, invented in 1817 byCarl Friedrich Gauss as an improvement to theFraunhoferAchromatic telescopeobjective lens by adding ameniscus lens to its singleconvex andconcave lens design.[2]: 117–118 Alvan Graham Clark andBausch & Lomb further refined the design in 1888 by taking two of these lenses and placing them back to back, making a "double Gauss" design,[3] albeit with indifferent photographic results.[2]: 118
Current double Gauss lenses can be traced back to an 1895 improved design, whenPaul Rudolph ofCarl Zeiss Jena thickened the interior negative menisci and converted to them to cementeddoublets of two elements of equal refraction but differing dispersion for theZeiss Planar design of 1896[4] to correct forchromatic aberration. It was the original six element symmetricf/4.5 double Gauss lens.[2]: 121–122 Horace William Lee added a slight asymmetry to the Planar in 1920, and created theTaylor, Taylor & Hobson Series 0 (also called theLee Opic, UK)f/2 lens.[2]: 122 It was commercially unsuccessful, but its asymmetry is the foundation of the modern double Gauss, including the ZeissBiotar.[1]: 243–245
Later the design was developed with additional glasses to give high-performance lenses of wide aperture. The main development was due toTaylor Hobson in the 1920s, resulting in thef/2.0Opic and later theSpeed Panchro designs, which were licensed to various other manufacturers. In 1927, Lee modified the Opic design and increase the maximum aperture up tof/1.4, which was named theUltra Panchro lens. Further improvement was done by Lee in 1930, theSuper Speed Panchro.[5] It was af/1.5 fast design with seven elements in five groups, which influenced later fast speed lens designs, being cited by many lens manufacturers until the 1960s.
TheBiotar is another competitor of BritishPanchro series. In the same year of 1927, Zeiss designed theBiotar 50mmf/1.4[6] for cinematography. Its still photography version, the ZeissBiotar 58mmf/2 (Germany) appeared on the Ihagee Kine Exakta (1936, Germany), the first widely available35mmsingle-lens reflex cameras, in 1939. It was also the standard lens on theVEB Zeiss Ikon (Dresden) Contax S (1949, East Germany), the first pentaprism eye-level viewing 35mm SLR.[7] TheBiotar, originally designed in 1927, had a six element asymmetric double Gauss formula. Post-World War II Zeiss (Oberkochen, West Germany) no longer uses theBiotar name; instead lumping all double Gauss variants under thePlanar name. The Soviet 58mmf/2Helios-44 lens of theZenit camera was the most common version/clone of theBiotar,[8] making an excellent value-for-money accessory today for any digital camera with APS-C and Full-Frame sized sensor, though an appropriate M42 adaptor is required for this particular lens.
Several contemporaneous competing, but less famous lenses, were similar to the Biotar, such asAlbrecht Tronnier'sXenon forSchneider Kreuznach (1925, Germany).[2]: 122–123 [9] For example, three asymmetric Double Gauss lenses were produced in 1934 for Ihagee VP Exakta (1933, Germany) the type127 roll filmSLR camera: 8 cmf/2 versions of both theBiotar andXenon, as well as the DallmeyerSuper Six 3 inchf/1.9 (UK).[10]
Other early Double Gauss variants for 35mm cameras included the KodakEktar 45mmf/2[11] on the Kodak Bantam Special (1936, USA), the KodakEktar 50mmf/1.9[12] for the Kodak Ektra (1941, USA), the VoigtländerUltron 50mmf/2[13] on the Voigtländer Vitessa (1951, West Germany) and the LeitzSummicron 50mmf/2[2]: 125 for theLeica M3 (1953, West Germany). A notable, but largely-forgotten, use of the Double-Gauss formula was in the Canon 28mmf/3.5 (1951, Japan)[14] in M39 mount for Rangefinder cameras. By enlarging the rear group significantly (compared to a Double-Gauss type of more traditional focal length), the field of view was increased while keeping the aperture relatively large- making it, for a time, the fastest 28mm lens available for 35mm cameras by a large margin.[15]
In 1966,Asahi Pentax combined theSuper Speed Panchro type and theXenon type, developing the seven-element, six-groupSuper Takumar 50mmf/1.4 (v2).[16] During the 1960s to early 80s every optical house hadSuper Panchro type orSuper Takumar type double Gauss normal lenses jockeying for sales. For example, compare the Tokyo OpticalRE Auto-Topcor 5.8 cmf/1.4[17] for the Topcon RE Super/Super D (1963), OlympusG. Zuiko Auto-S 40mmf/1.4[18] for the Olympus Pen F (lens 1964, camera 1963), YashicaAuto Yashinon DX 50mmf/1.4[19] for the Yashica TL Super (1967), Canon FL 50mmf/1.4 (v2)[20][21] for the Canon FT (lens 1968, camera 1966), Asahi OpticalSuper Takumar 50mmf/1.4 (v2)[22] for the Pentax Spotmatic (lens 1968, camera 1964), FujiFujinon 50mmf/1.4[23] for the Fujica ST701 (1971), Minolta MCRokkor-PG 50mmf/1.4[24] for the Minolta XK/XM/X-1 (1973), ZeissPlanar HFT 50mmf/1.4[25] for the Rolleiflex SL350 (1974), KonicaHexanon AR 50mmf/1.4[26] for the Konica Autoreflex T3 (lens 1974, camera 1973) and Nippon KogakuNikkor (K) 50mmf/1.4 (New)[27] for the Nikon F2 (lens 1976, camera 1971); all from Japan except the Zeiss which was designed in West Germany.
Zoom lenses have been dominant since the 1980s and so there have been few newly designed Double Gauss normal lenses, but many new prestige low production Double Gauss lenses have been released. Compare the Canon EF 50mmf/1.2L USM (2007, Japan),[28][29] NikonAF-S Nikkor 50mmf/1.4G (2008, Japan/China),[30] Sigma EX DG HSM 50mmf/1.4 (2008, Japan),[31] (Cosina) VoigtländerNokton 50mmf/1.1 (2009, Japan),[32]Leica Noctilux-M 50mm f/0.95 ASPH (2009, Germany)[33] with their antecedents, or SLR MagicHyperPrime 50mm CINE T0.95 (2012, Hong Kong, China).[34]
The design is presently used in inexpensive-but-high-quality fast lenses such as theSony FE 50mmf/1.8, theCanon EF 50mmf/1.8 and theNikon 50 mmf/1.8D AF Nikkor. It is also used as the basis for faster designs, with elements added, such as a seventh element as in both Canon[35] and Nikon's 50 mmf/1.4 offerings[36] or an aspherical seventh element in Canon's 50 mmf/1.2L.[29] The design appears in other applications where a simple fastnormal lens is required (≈53° diagonal) such as in projectors.