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Carl Zeiss Lens Design 7-2-99Alexander Lee

Overview

This list is only for designs that the Carl Zeiss Foundation has some nominal claim on the origin of design.

I created this list for a few reasons.

  • First because I was interested in the design criteria that Zeiss uses when building lens of different focal lengths, or same focal lengths but different speeds or physical size. As I felt it may have an impact on optical quality, I figured it would be good to know the family traits of lens designs for when I am shopping for new lenses.
  • Second,  there have been few groundbreaking lens designs since the Biogon was developed in the 1950's.  Most modern lens are based on modified older designs, or older designs reworked with modern glass and multi-coating in mind.  The most common lens design still is the almost 100 year old tessar type.
  • Third,  I thought it was a pretty interesting field that was not very well covered.

It was hard getting the data. Apparently there are some good books out, but my local library doesn't have them, and I'm too lazy to find it in other library systems have them request it via interlibrary loan. Most of my data came from "classic" large format lens FAQ's and various Contax/Hassleblad/Rollie lens propaganda, though the propaganda really only touted the praises in vague terms, and didn't mention any potential design limitations.

Recently, I picked up Rudolf Kingslake's excellent book "A History of the Photographic Lens", ISBN 0-12-408640-3 and am in the process of revising my data.   Hopefully, I will also get Rudolf Kingslake's Modern Photographic Lens Design book as well, but I already have more material to work with than I have time to deal with it.

Misc. background on CZ lens

Bausch and Lomb was licensed to produce CZ lens in America for a while. They developed and acquired patents for several variants of CZ lens designs. Most patents back then were good for 17 years, though during the years when the USA was at war with Germany, the assets of German companies in America were put into a federal trust which managed the property, real and intellectual, until the end of the war.  During that time, the federal agency could allow American companies to use the property for the war effort, or they could lease the property out.  A notable example was the Leica New York repair facility.  The government trust originally wanted Kodak to assume control of the repair facility to produce Leica copies using the tools and dies.  Kodak wisely turned the offer down, avoiding legal problems after the war, as well as the fact that it was potentially (and actually turned out to be for the company that agreed to the offer) a money loosing proposition.

Ernst Abbe was hired by Carl Zeiss in 1866 to help Zeiss manufacture instruments in a proper scientific basis.  in 1880, he hired Otto Schott to help develop new types of glass.  They established Jena Glassworks in Jena Germany, and by 1886, they had a catalogue of 44 types of glass, many of which were new.  They manufactured the first successful high-index crown glasses.  These new glasses allowed lenses to be made that had a flat field free from astigmatism.

The Tessar design was produced in 1902, and awarded a US patent in 1903.  When the patent expired in 1920 there were many variants on the Tessar design released other companies, such as some of Kodak's Ektars and Schneider's Xenars. The famous Leica 50mm f/3.5 Elmar lens released in 1920 was a Tessar type lens.  After Leica introduced the first 35mm camera in 1925, Zeiss's camera division knew that they were behind in small format camera development responded a year later by acquiring four camera manufacturers a year later in 1926, Ica, Contessa-Nettel, Ernemann and Goertz and merging them into Zeiss Ikon AG.

After Zeiss absorbed Goertz in 1926, the American Goertz division became an independent company (Goertz American Optical Co.) and continued to make Goertz lens, as well as innovate new lenses. Goertz American Optical Co. was renamed to Goertz Optical Co. Inc. in 1964, purchased by Kollmorgen in 1971, then in turn, Kollmorgen was purchased by Schneider in 1972.

The first commercially viable lens coating process, but depositing a thin layer of low index material (originally calcium fluoride or magnesium fluoride) was developed by A. Smakula of Zeiss in 1936. Zeiss did not invent the concept and function of lens coating as the Contax website history wording would lead you believe. H. Dennis Taylor in 1896 observed that old lenses that had become tarnished by exposure (a natural bloom coating) transmitted more light than a newly polished lens.  He postulated that the layer of tarnish had a lower refractive index than the glass, and therefore reflected less light and transmitted more if it.  He was awarded the first patent for lens coating in 1903 for a chemical or acid fuming process that was highly unreliable, and the components very caustic.  Viable lens coating allowed Zeiss's (and everyone else's) more complex lens designs to be implemented with much less flare and greater contrast. Previously those designs, while very much corrected for aberration and astigmatism suffered very poor contrast. The lens coating technology was considered a national security secret during W.W.II, and did not really become available to consumers until after the war was over.   This coating though was a single layer that usually reduced the reflectivity of one wavelength of light.  Light of other wavelengths were less affected the further up or down the spectrum from the prime wavelength.  Later, plans to deposit multiple layers of coating allowed a more even reduction of reflectivity through the entire spectrum of photographical light.  Leitz was the first company to sell a regular production multicoated lens to general consumers.

After W.W.II, the Allies brought the heads of the Carl Zeiss foundation, as well as key Zeiss foundation personnel from Dresden to West Germany, because they recognized the value of the optical knowledge and research that Carl Zeiss had, as well as the cold war desire for the technology not to fall into Communist hands. The Carl Zeiss foundation was moved to Western Germany (legal paper work here, not equipment) from Dresden as well. This was important because later, it allowed the Carl Zeiss Foundation to successfully press claim to various trademarked names, such as Zeiss, Carl Zeiss, and Contax.  The Schott glassworks was slit into Jena Lenswork, in Russian hands, and Schott in Oberkochen.

The lensworks and camera factories in Dresden were destroyed in the Firebombing of Dresden February 14, 1945, but the Jena camera works continued to produce lens and cameras under the Carl Zeiss name until the trademark dispute between the East Germany company, and the West German was resolved.  Some of the existing machinery was disassembled by Russian troops for war reparations, and were re-assembled in the newly forming USSR.   The East German Carl Zeiss continued to produce cameras and lens from existing stocks of parts.  Later they released a new line of SLR cameras labeled Carl Zeiss Dresden, the Contax S and Contax D.  Eventually after the trademark dispute was settled, the eastern Contax SLR was renamed the Pentacon.  Into the 70's, the East German Carl Zeiss had lens produced in Japan for several systems labeled Under License from Carl Zeiss Jena. 

Since the re-unification of Germany, the Eastern and Western Zeiss companies have been re-united, and the headquarters is being moved back to Jena.  The massive Jena optical factory which at it's height in Eastern Germany employed over 60,000 factory workers has been broken up and parts have been sold off.  The binocular section has been sold to Dr. Optik, and Schneider has purchased part of the Glassworks.

Symmetrical lenses
Meniscus lens with a stop in front exhibits barrel distortion, if turned around with the stop behind the lens, it reversed into a pincushion.  If two were mirrored around the stop, the distortions cancel each other and leave a distortion-less system.  It also corrects for lateral color (chromatic difference of magnification) and coma.  Truly symmetrical lenses must be used at 1 to 1 magnification to totally cancel the three aberrations, and exhibit some very small amounts of transverse aberration at infinity.

Asymmetrical lenses
Asymmetrical lenses, while not totally corrected for those three aberrations, can allow larger apertures and cover wider fields than symmetrical designs.

Dialyte - Airspaced Achromatic doublet.

Lens Designs

ABBE-RUDOLPH APOCHROMATIC TRIPLET
1890
E. Abbe & P. Rudolph
Zeiss
A lens consisting of a thick cemented triplet between two symmetrical periscopic lens.  While well corrected for axial distortion, it suffered from severe astigmatism, and was never sold.
ANASTIGMAT / PROTAR
1890
Paul Rudolph
Zeiss
The Zeiss Anastigmat consisted of an old-achromat (cemented doublet made with a high-index fling glass and a low-index crown glass) front with a  new-achromat (cemented doublet made with a high-index crown glass and a low index flint glass, making a flat field lens free from astigmatism) in the rear.  This was the first lens designed specifically for photographic applications at Carl Zeiss.
There were 5 series with slightly different formulations, and two sub-variations.
The Double or Quadruple Anastigmat Series VII was a design with a cemented quadruplet lens   .It could be designed to have a "convertible" focal lengths (the rear component could be use d alone or in combination with a similar front component of the same or different focal length).
Zeiss licensed several companies to manufacture these lenses:
Bausch and Lomb, Rochester, New York
Krauss, Paris, France
Ross, London, England
Fritsch, Vienna, Austria
Koristka, Milan, Italy
Suter, Basle, Switzerland

As other companies manufactured lenses called Anastigmat, Zeiss lost the trademark to the name, so in 1900, Zeiss re-named their  lens Protar.  The performance was not as good as they wanted, and shortly other superior lens designs came onto the field.
DAGOR
1892
Emil Von Hoegh
Goerz
Designed by Emile Von Hoegh of Goertz in 1892. The design was supposedly offered to Zeiss, but they turned it down.  The design was sold go Goerz, and the design was considered so good, they offered von Hoegh a position as their principal lens designer, to succeed Carl Moser, who had recently died.  The original name was Dobel (double) Anastigmat Goerz, which was reduced to the Dagor acronym in 1904.  Within two month of the Dagor patent application, Rudolph of Zeiss applied for a practically identical patent which was never issued.  Zeiss produced the Statz Anastigmat for a while that was nearly identical to the Goerz Dagor, but they replaced it with the Anastigmat Series VII.

The design consisted of two symmetrical cemented triplets (6 elements in 2 groups) in which the two outer elements are positive, one of the inner elements was used to correct spherical aberration and the other used to flatten the field.  As there are only 4 glass to air transmission surfaces there was minimal flare and better contrast. Reputed to have good sharpness and large image circles, though there is softness at the periphery of coverage. Many Dagor designs are made so that the the circle of illumination is vignetted and the circle of good definition covers the entire film surface (with no shifts). It is more of a wide field design (+/- 30 degrees at f/6.8), rather than a wide angle design.  Some designers (Zeiss Ortho-Protar, the wide angle Schneider Angulon) reversed the triplets, in which the outer elements were negative. The reversed type is thicker than the normal Dagor, leading to the risk of excessive vignetting.  Schneider avoided the vignetting problem by making the outer surfaces much larger than the diameter of the axial beam.

Some well known variants are:

  • Zeiss: Orotho-Protar, Statz Anastigmat Series VI
  • Schneider: Angulon
PLANAR
1896
Paul Rudolph
Zeiss
Designed by Dr. Paul Rudolph in 1896 based on the double Gauss design (in 1817, C F Gauss described a telescope objective consisting of a pair of meniscus shaped elements, one positive, and one negative.) The design was 4 groups of 6 elements, and a flat field design. Symmetrical optical configuration producing low spherical aberration and astigmatism. The normal wide airspace separating the positive and negative elements in the double gauss design made a large amount of spherical aberration.  Rudolph thickened the negative elements and reduced the airspace as much as possible, which corrected the spherical aberration and the sagittal/ tangential astigmatic aberration.   Rudolph also inserted a "buried surface" into the thick negative elements of a cemented interface separating two type of glass having the same refractive index, but different dispersive powers.  Not widely used until coating processes were available, due to light loss from the large number of transmission surfaces causing very low contrast. Due to it's complexity and high number of transmission surfaces, it really did not come into it's own until coating was developed. The planar was used as a base for lens derivatives, though in asymmetric form.  Almost all the high-aperture lenses supplied on Japanese cameras are modification on the Planar.

Some well know variants of six element Double Gauss designs are:

  • Agfa: Soligon
  • Angenieux: S-type
  • Astro: Kino, Tachar
  • Bausch & Lomb: Aminar, baltar, Raytar
  • Boyer: Saphir
  • Dallmeyer: Super Six
  • Enna: Annaston
  • Isco: Westagon
  • Kinoptik: Apochromat, Fulgior
  • Kodak: Ektar, Aero Ektar
  • Leitz: Elcan, f/1.2Noktilux, Sumarrit, Summar, Summitar, Summicron, Dygon
  • Meyer: Domiron
  • Rodenstock: Heligon
  • Ross: Xtralux
  • Schneider: f/2 Xenon, Xenogon
  • Steinheil: Quinon
  • Taylor-Hobson: Amotal, Ivotal, Kinic, Opic Panchrotal, Speed Panchro
  • Wollensak: Raptar
  • Wray: Copying Lens
  • Zeiss: Biotar, Flexon
UNAR
1899
Paul Rudolph
Zeiss
Paul Rudolph replaced both cemented interfaces in his anastigmat design with narrow airspaces, producing the Unar. It was a hybrid design, in which the rear type was a Gauss type with two single meniscus elements, while the front half was a dialyte. The air spaces in the shape of a positive lens helped correct spherical aberration, and allowed designers a larger choice of glass, as they can use glasses with the same refractive index on both sides of the air space.  Using glasses of identical refractive lenses cemented together would effectively make one big useless lens..
HELIAR
1900
Hans Harting
Voigtlander
Hans Harting came up with this design while trying to create a symmetrical modification of the Cooke Triplet (in 1893 H. Dennis Taylor developed the triplet.  Taking a thin positive element and a thin negative element and putting them together would neutralize each other, and create a zero Petzval sum.  Separating the lens, the system would acquire a positive power, but the petzval sum is unchanged.   The highly asymmetrical arrangement would have poor oblique aberrations, so Taylor suggested splitting one of the elements in half, and mounting each have on opposite sides of the other element.)  Consisting of 5 elements in three groups, Harting replaced the single rear element of the Triplet with a cemented doublets, allowing him to correct for spherical, chromatic, astigmatic aberrations and the Petzval sum, leaving the symmetry of the lens to correct the three transverse aberrations.  The original patent had a heavy coma when used on distant subjects, so two years later, Hartig came out with an asymmetrical version of the lens.  In 1903, Hans Harting reversed the outer components around so the cemented interfaces were convex towards the stop instead of concave, which was slightly worse in astigmatism but otherwise better.  In 1903 as well, Hans Harting patented a hybrid design called the Oxyn in which the front element was similar to the Heliar, while the rear doublet resembled the Dynar.  At low apertures, the Dynar was an excellent lens.  In 1919, Dallmeyer produced a Dynar type  lens called the Pentac with a high aperture of f2/9.  While the field was slightly inward curving, the lens was excellent in every other respect.  After World War I, Voigtlander revived the Dynar type but felt the Heliar name was preferable.
HYPERGON
1900
????
Goerz
The Hypergon is an extreme wide angle lens (+/- 67 degrees) covering a flat field.  It is of symmetrical construction consisting of two deep meniscus elements that almost form a sphere.  The aperture was limited to f/20 due to the spherical and chromatic aberrations.  As well, there is a large amount of light falloff from the center, requiring a a cog wheel which spun by air for most of the exposure then swung out of the way in order to allow even exposure.  Currently Canham is producing these lenses, but with adjustable waterhouse stops, and a center filter instead of a cog wheel.
TESSAR
1902
Paul Rudolph
Zeiss
Designed by Dr. Paul Rudolph in 1902, utilizing the rear cemented doublet of the Anastigmat and the airspaced front component of Unar.  The front element was of very low power, like the Anastigmat design, and it's sole function was to correct the remaining aberrations of the strong g new-achromat rear component.  The cemented rear component reduces zonal spherical aberration, reduces overcorrected oblique spherical aberration, and reduces the gap between astigmatic foci at intermediate field angles.   The first design was f/6.3, but by 1917 the aperture was raised to f/4.5, and in 1930, W. Merte and E. Wandersleb raised it to f/2.8.  The 50mm f/3.5 Elmar lens fitted to the early Leica cameras was a Tessar type designed by Max Berek in 1920.   The US patent was received 1903, giving Zeiss a monopoly on the design until 1920, the end of World War I. Uses a 4 elements 3 group design, light, small, relatively high resolution, inexpensive to produce comparatively to other designs. Designed to be sharp at most apertures, but has limited coverage. It was widely copied and many variants made as it was seen as a good compromise between the Dagor and Artar designs for coverage, sharpness, and contrast.

Some more notable lens of the Tessar type have appears under the following names, though some of the names are of a product family also include other lens designs:

  • Agfa :Solinar
  • Berthiot: Flor, Ilor
  • Boyer: Saphir
  • Busch:Glyptar
  • Dallmeyer:Dalmac, Perfac, Serrac
  • Erenmann: Ernon
  • Hermagis: Hellor, Lynx
  • Ilex: Paragon
  • Kodak: Ektar
  • Laak: Dailytar
  • Leits: Elmar, Varop
  • Meyer: Primotar
  • Playbel: Anticomar
  • Rodenstock: Ysar
  • Ross: Xtralux
  • Roussel: Stylor
  • Schneider: Comparon, Xenar
  • Tayer-Hobson: Apotal, Ental
  • Voigtlander: Heliostigmat, Skopar
  • Wollensak: Raptar
  • Wray: Lustrar

Some variation were produced which allowed companies to bypass the copyright.  One   in which the lens is turned around so the cemented doublet is in front, and the airspaced element behind was made by several manufacturers.  Another was using a cemented triplet in the rear instead of a doublet.  The Voigtlander Heliar and it's variations could be considered a modified tessar, but it was produced before the announcement of the Tessar, and was a modification of the Triplet lens design.

ALETHAR
1903
W. Zschokke
Goerz
This design was a symmetrical apochromatic process lens for graphic arts.   It was a basic dialyte type, but with cemented triplets in place of the inner negative elements.  Due to the primitive glass used, it did not live up to it's billing as an apochormat, and was soon discontinued.
ARTAR
1904
W. Zschokke
Goerz
After the failure of the Alethar, Walter Zschokke and F. Urban, designed a much simpler Artar.  It is based on a 4 element air-spaced type lens called a "dialyte" (dialyte is a design by Emile Von Hoegh), so is sharp across entire field of illumination
The positive elements were a dense barium crown, and the negative elements were made of telescope flint glass.  Designed to be apochromatic for use in three color graphics arts. It has a narrower field of coverage than Tessar. This lens was the regular Goerz process lens for almost seventy years. Current modern implementations of this design are the Nikkor M series LF lens and the Schneider G-Claron's.
ERNOSTAR
1919
Ludwig Bertele
Ernemann Co.
In an attempt to raise the aperture of the Cooke Triplet, Charles C. Minor inserted a positive meniscus element into the front airspace.  Ludwig Bertele decided to also work on the Cooke triplet with Charles C. Minors modification.  His design consisted of cemented doublets for the front two elements.  It was the first f/2 lens, and the first lens with an aperture large enough for candid available light photography.  in 1920, he was able to improved his design to make the f stop size 1.8.  He also developed a simpler model with a f-stop of 2.7.
BIOTESSAR
1925
E. Wansersleb & W. Merte
Zeiss
A variation of the Tessar, consisting of a cemented doublet in the front, a single negative element, and a cemented triplet in the rear.
MAKRO PLASMAT
1926
???
Zeiss
The design was a hybrid in a f/2.9 setting.  The 6 element Gauss type had the rear three elements separated with air spaces.  It was made for many years and was a popular lens.
SONNAR
1930
Ludwig Bertele
Zeiss
Ernemann Company was taken over by the Zeiss-Ikon combine, and shortly in 1930, Ludwig Bertele started the design of the Sonnar type lens based on the second (f/1.8) Ernostar type.  It was completed in 1931, and was a f/2 Sonnar.  The sonnar negative triplet consisted of a high-index outside and a lower-index element between.  In 1932, he released a f/1.5 version with a strong cemented interface on the rear component.  This allowed correction on the higher-order spherical aberration which was needed in a lens of the high aperture.  The name Sonnar had been used previously by the Contessa Company for a camera with a Tessar type lens, but as Zeiss-Ikon absorbed Contessa, they acquired rights to the name.  The design uses less elements than Planar, so when coating tech was primitive, the lens had much less flare due to less surfaces in design. Simpler than Planar, smaller and comparatively inexpensive. Good contrast at edges at all apertures. Exhibits some softness at wide apertures. Sharp when stopped down.
MINIATURE PLASMAT
1931
Paul Rudolph
Zeiss
This was a Hybrid lens type, consisting of a front component which was a ordinary two meniscus element Gauss type, and the rear component was the rear half of a Plasmat.  It was a design of no particular strength and was not produces for long.   The lens arraignment was revived by Ludwig Bertele in his design of a f/2.7 lens for the Contax 35mm camera.  He called the design a Biogon, which was later re-used by Zeiss
R-BIOTAR
1932
Willy Merte
Zeiss
This was a high aperture narrow angle lens that was a variant of the Petzcal lens
TOPOGON
1933
Robert Richter
Zeiss
This was a double Gauss design arranged in a symmetrical design.   Due to it's wide angle coverage, and the small, though present, distortion, it, and the slightly modified form of Bauch and Lomb, called the Metrogon, became the standard aerial lens until the Wild Aviogon displaced it in 1952.  It covered a full 90 degree field at f/6.3, and in it's 6 inch size, it covered the 9"x9" format which was used in aerial photography and photogramy.  The 12 in size was also made to cover a 18"x18" format.

Some more notable lens of the Topogon type have appears under the following names, though some of the names are of a product family also include other lens designs:

  • Bauch and Lomb: Metrogon, Process Anastigmat
  • Boyer: Perle
  • Busch: omnar
  • Dallmmmeyer: Wide-Angle Anastigmat
  • Goerz: Geotar, Rectagon
  • Hermagis: Dellor Series D
  • Ilex: Anastigmat Series D
  • Kodak: Wide-field Ektar
  • Laak: Wide-angle Dialytar
  • Meyer: Aristostigmat
  • Plaubel: Wide-angle Orthar, Pecostigmat
  • Rietzschel: Dialyte
  • Rodenstock: Eurynar, Luminar, Ronar
  • Ross: Homoentric
  • Schneider: Isconar
  • SOM: Aquilor
  • Wollensak: Wide-angle Raptar
  • Wray: Wide-angle Copying Lens
  • Zeiss: Kekla, Topogon
PLEON
19?? (WWII)
????
Zeiss
Designed for wide-angle Aerial photography, this lens covered +/- 65 degrees.  It had considerable barrel distortion, which was removed by printing the negative in a special distorting printer.  The height of the Pleon followed the Fish-eye lens law, so the illumination was not uniform, but it was better than if the design was designed distortion-less.
BIOGON
second, current form
1951
Ludwig Bertele
Zeiss
Designed by Dr. Ludwig Bertele in 1951 based on a double-ended reversed-telephoto objective designed by M.M Roosinov (M.M Roosinov had that general patent in 1946 which consists of a central positive structure with one or more large negative menisci at each end making a roughly symmetrical arrangement),  for a ultra-wide angle lens for Zeiss to use on their Zeiss' Contax 35mm camera and on Hasselblad's cameras.  The design was physically large, being two focal lengths in length and one focal length in diameter. Zeiss's Biogon had two menisci at the front, and a single strong meniscus element at the rear.  The rear element is close to film plane for low distortion and better contrast, but interferes with mirror for SLR.  Because a master patent could not be obtained for the lens design, other companies used this excellent design, such as Schneider's Super Angulon, with one menisci at each end.  The design is similar to the Aviogon lens that Dr. Bertele designed in 1952 for Aerial photography for the Wild Company of Heerbrugg in Switzerland with two menisci at each end.  The Wild Aviogon was first produced in a 115mm focal length to cover a 18cm square, and with distortion of less than 10 microns at any point in the field, quickly became the standard lens for aerial photography and photogrammetry.  Bertele patented a variant on the design with three meniscus elements on each end which covered about 120 degrees of total field.

Some more notable design variants

  • Schneider: Super Angulon
  • Wild: Aviogon
  • Zeiss: Hologon
HOLOGON
1966
Erhard Glatzel
Zeiss
Designed by Dr. Erhard Glatzel in 1966, it is really a modification of the Biogon lens design. 5 elements in 3 groups. The rear element is close to film plane for better contrast, but interferes with mirror for SLR. There is significant light falloff at edges, so it is frequently used with ND center graduated filters. Current implementations are a 15.5mm and 16mm f8 fixed aperture lens.  I believe that the 16mm is really the 15.5mm rounded off.  At f/8 the lens covers a flat field of +/- 55 degrees without distortion.
DISTAGON
????
????
Zeiss
This is a reversed telephoto lens, consisting of a large negative lens in front of an ordinary lens.  This allows it to obtain a short overall focal length with elements of a larger and more manageable size, helps design a system that is favorable for both high relative aperture and wild-angular field, and increased the back focal distance beyond it's usual magnitude, which give space for the mirror of a SLR. The downsides are that is must be physically large, and of complex construction to correct all the aberrations, making the lens more expensive to produce.    Reversed telephoto designs are rarely over 2 inches in focal length, and then it is only used for specific applications.  Compared to the Biogon, it has a larger circle of illumination full aperture, though softer when wide open, though it is sharper when stopped down. Rear element does not interfere with mirrors in SLR's

Some definitions of terms I use in the list

  • Aberrations - Aberrations are image defects that result from limitations in the way lenses can be designed. Better lenses have smaller aberrations,but aberrations can never be completely eliminated, just reduced. The classic aberrations are:
    • Spherical aberration. Light passing through the edge of the lens is focused at a different distance (closer in simple lenses) than light striking the lens near the center.
    • Coma. Off axis points are rendered with tails, reminiscent of comets, hence the name. It can be shown that coma must occur if the image formed by rays passing near the edge of the lens has a different magnification than the image formed by rays passing near the center of the lens.
    • Astigmatism. Off-axis points are blurred in their the radial or tangential direction, and focusing can reduce one at the expense of the other, but cannot bring both into focus at the same time. Think of it as the focal length as varying around the circumference of the lens. (Optometrists apply the word "astigmatism" to a defect in the human eye that causes *on-axis* points to be similarly blurred. That astigmatism is not quite the same as astigmatism in photographic lenses.)
    • Curvature of field. Points in a plane get focused sharply on a curved surface, rather than a plane (the film). Or equivalently, the set of points in the object space that are brought to sharp focus on the film plane form a curved surface rather than a plane. With a plane subject or a subject at infinite distance the net effect is that when the center is in focus the edges are out of focus, and if the edges are in focus the center is out of focus.* Distortion (pincushion and barrel). The image of a square object has sides that curve in or out. (This should not be confused with the natural perspective effects that become particularly noticeable with wide angle lenses.) This happens because the magnification is not a constant, but rather varies with the angle from the axis.
    • Chromatic aberration. The position (forward and back) of sharp focus varies with the wavelength.
    • Lateral color. The magnification varies with wavelength.
  • APO or Apochromatic - The distance behind the lens at which monochromatic light (light of a single wavelength) comes to focus varies as a smooth function of the wavelength. If this function has a zero derivative in the visible range, and hence if there are two wavelengths at which the light comes to focus in the same plane, the lens is called achromatic. If there is a higher order correction, usually with the result that 3 or more visible wavelengths come to focus at the same distance, the lens is called apochromatic. Some authorities add more conditions. Apochromatic lenses often contain special low-dispersion glasses. APO is an abbreviation for apochromatic.
  • Asymmetrical - Front and rear lens groups of lens are not the same.
  • Cells - Sets of lens groups designed to function as a unit
  • Circle of good definition - Effective circumference of coverage that is usably sharp.
  • Circle of illumination - Effective circumference of coverage that has useable/recordable light
  • Coating - Before coating, each transmission surface resulted in about a 4% to 8% loss of light to reflection depending on the refractive index of the glass. So an uncoated Dagor or Protar with four transmission surfaces looses 15% to 29% of the light to flare. An uncoated Tessar looses 22% to 40% of the light to flare. An uncoated Planar with eight surfaces looses 28% to 49% of light to flare. The flare would exhibit itself on the film as unfocused non-image forming light which reduced the contrast of the picture.
    • Single Coating - After single coating, this dropped to about 2% to 4% loss of light per transmission surface. Applying the coating at quarter wavelength thickness could greatly increase the effectiveness of the coat, but it could completely block some wavelengths of light and partially block others. Typically blue-green wavelengths were suppressed with an amber coat, or green wavelengths with a purple coat.
    • Multi-coating - Multicoating was first done as two separate coats at different wavelength thickness on different transmission surfaces to balance the color of the light transmitted to the film. Later, multi-coating as we know it, one coat stacked on another (first used on a production lens by Leitz) reduced the light lost to diffraction further to about 1/2% to 1% per transmission surface. The classic second coat was bismuth oxide again applied at quarter wavelength thickness for a different wavelength, typically orange-yellow for the second coat and green-blue for the first coat giving a faint green reflection. A multi-coated Planar could now only loose about 4% to 8% of the light to flare, quite a difference.

    Coating and multicoating allowed designers to use more complex designs with more air spaces which allowed easier design for correction of spherical aberrations. The difference between uncoated lenses and coated lenses are great, the difference between single coating and multi-coating is visible, but not nearly as great as the first leap from uncoated to coated. Coating and multicoating opened the way for many otherwise unfeasible modern lens designs, such as complex wide-angle lenses, big multi-element zooms, and lots of marketing hype. Coating still won't save you from nasty flare in certain lighting conditions, such as shooting into the sun, so make sure to use those lens shades!

  • Convertible Lens - A set cells that can be combined together in different pairs or singly to produce different effective focal lengths. Each cell must be able to correct and focus the image properly on the film alone. If a cell is used singly, it is mounted behind the shutter.
  • Elements - individual lens
  • Groups - single lenses or groups of lenses cemented together
  • Symmetrical - Front section of lens is identical mirror image of rear section. Because of this, aberrations and astigmatisms are minimized. Inherently optimized for 1:1.
  • Transmission surfaces - Lens element to air surface.

Source information

Classic vs. Modern Lens

  • Basic lens questions, by John Sparks
  • Importance of corrections for color vs. B&W Richard Knoppow
  • Untitled by Timothy Takahashi
  • Untitled by Barry Sherman
  • Untitled by Alan Heldman
  • Untitled by Thor Lancelot Simon
  • Untitled by Pete Bergstrom
  • Untitled by Mark
  • Untitled by Eric Volpe
  • Untitled by Edward M. Lukacs
  • Untitled by Richard Knoppow

Contax USA Website

More on Classic lenses

  • Untitled by Richard Knoppow
  • Untitled by Larry Whatley

Lens FAQ by David Jacobson

View Camera (unknown vol. and issue, will add the info when I dig up the magazine)

A History of the Photographic Lens by Rudolf Kingslake, copyright 1989, Academic Press Inc. ISBN 0-12-408640-3