Zeiss Distagon 2.8-15  copy

A Comprehensive Guide to Camera Lens Design and Zeiss Nomenclature

The German optical systems manufacturer, Carl Zeiss, has had a 168 year legacy in creating some of the world’s best lenses. In 2011, H.H. Nasse wrote a series of technical papers for Carl Zeiss detailing their modern lens history and genealogy. In his three part series, he discussed 5 lens designed that changed the world. They are the Planar, the Tessar, the Biogon, the Distagon, and the Hologon (click on these links to download the original PDF files).

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Zeiss Planar 100mm f/2 (left); Zeiss Planar 85mm f/1.4 (center); Zeiss CP.2 25mm f/2.9 Cine Lens (right)

While very detailed and technical, it is a difficult read for your average Joe. That’s why, we have repackaged the information in a more reader friendly format and filled in some holes with our cited research (such as adding the missing Sonnar lens). That being said, I still recommend you read Nasse’s original papers after you read this article. They are filled with interesting tidbits about optics and engineering.


Zeiss Normal and Telephoto Designs

A normal/standard lens means its focal length is about the diagonal length of the image capturing area. For 35mm film and Full Frame cameras, that translates to 24x36mm with a diagonal of 43.3mm. This means, lenses with focal lengths near 43.3mm can be considered normal lenses. We usually consider lenses between 35mm – 60mm as normal lenses.

Planar (1896)
Planar_1896
The symmetrical design places the aperture (represented by the vertical line) between the two groups of elements, allowing for wider apertures than other designs. The 8 air-to-glass surfaces, unless effectively coated, reduce contrast and introduce flaring and ghosting.

This legendary Zeiss design trademarked Planar (also known as Biotar or Biometar in E. Germany’s Carl Zeiss Jena) is derived from, and suggests, a “plane/flat” field curvature. Most of the world’s fastest lenses today are derivatives of the Planar design, including:

  1. The $11,000 Leica 50mm f/0.95 Noctilux
  2. The ultramodern Zeiss Otus 85mm f/1.4
  3. The fastest lens in the world, the Zeiss 50mm f/0.7 Stanley Kubrick used in the movie Barry Lyndon for its candlelit dinner table scene and NASA’s Apollo Program used to photograph the dark side of the moon.

In fact, every 50mm prime ever made by any manufacturer are essentially modified Planar designs.

nikon f2 cutaway
A cutaway of the Nikon F2 film SLR sporting a Nikkor 50mm f/1.4 in classic Planar design.

Advantages

  1. The symmetrical grouping allows for large aperture designs (f/2 or larger).
  2. A very flat field curvature which leads to sharpness across the entire image plane.
  3. Well controlled chromatic aberrations

Disadvantages

  1. More expensive to produce and heavier than Tessar designs
  2. The many air-to-glass surfaces require effective lens coatings to reduce flaring, ghosting, and to improve contrast.
  3. Prone to astigmatisms.
Tessar (1902)
Tessar
Only 4 elements in 3 groups make up the asymmetrical design.

Etymologically, the word Tessar is from the Greek word “tessares,” meaning “four,” which denotes the number of elements in its design. Derived from the older Protar and Unar designs, Tessar’s simplicity and compactness has made it extremely popular to the point that it is commonly found in today’s camera phones.

In fact, subsequent lenses designs such as the Leitz Elmars, Zeiss Sonnars, Kodak Ektars, Schneider Xenars, Voigltander Heliostigmats and Skopars, and the Nikon 50mm f/1.8D
are all modified Tessars. However, a lot of the Vario-Tessar zoom lenses you see on Sony compact cameras have nothing to do with the Tessar design.

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Advantages

  1. Smaller and less expensive to manufacturer
  2. Fewer air-to-glass surfaces means contrast is retained and flaring is avoided with less of a need for advanced coatings
  3. Anastigmatic (non-astigmatic) design naturally corrects for distortion, coma, and lateral chromatic aberration.

Disadvantages

  1. Subject to spherical aberrations, field curvature, and astigmatisms even at moderate apertures.
  2. Correcting for the above aberrations require additional elements which adds complexity and expense.
  3. Impractical for larger aperture designs.
Sonnar (1932) 
Sonnar
Asymmetrical design derived from the Tessar

The trademark Sonnar is derived from the German word “sonne,” which means “sun.” An adaptation of the Tessar design, the Sonnar’s characteristics brings out the best from the Planar and the Tessar designs. However, Sonnar lenses are incompatible with DSLR systems as the rear element would protrude into the mirror box. Thus, only rangefinders, mirrorless cameras, and some medium format cameras can enjoy the Sonnar design.

Sony-FE-55mm-f1.8-ZA-Carl-Zeiss-Sonnar-T-Lens-Construction copy
One of the best modern day lenses, the Zeiss Sonnar T* FE 55mm f/1.8

Advantages

  1. Compared to the Tessar, Sonnar designs can facilitate larger apertures while chromatic aberrations are reduced.
  2. Compared to the Planar, Sonnar designs have less air-to-glass surfaces such that contrast is improved and flaring is reduced.

Disadvantages

  1. Incompatible with SLRs and DSLRs
  2. Compared to the Planar, Sonnar naturally exhibits more aberrations and requires additional correction elements which adds complexity and expense.

Zeiss Wide Angle Designs

Zeiss wide angle lenses all share the common “-gon ending, which is derived from the Greek word “gonia” meaning “angle.” Wide-angle lenses also share at least two design challenges. First is the obliqueness of angle the light rays hit the focal plane. Second is the necessity of a retrofocus design.

Biogon (1936)
Biogon21
Nearly symmetrical wide angle

Back in the 1930s, the “Bio-”  in Biogon didn’t refer to biology as it would commonly today. It made reference to Biotar (another name for Planar as mentioned above), which was associated with dynamism and photographic quality.

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The size difference of a Biogon (left) and a Distagon (right) with the same focal length and aperture size.

Advantages

  1. Extremely compact compared to Distagon wide-angles.
  2. Excellent contrast and definition across the image plane.
  3. Very well controlled distortions and ghosting.

Disadvantages

  1. Light rays hit the corners of digital sensors at uncompensated oblique angles, causing color shifts and other anomalies.
  2. Vignetting is worse than Distagon even after stopping down.
  3. The thickness of integrated anti-aliasing and other filters in front of digital sensors significantly affect image corner quality if not calculated for. (Ed: Images shot with the Loxia 35mm f/2 will probably look different on the A7R versus the A7 or A7II).
  4. Incompatible with every SLR and DSLR design because the rear element protrudes into camera body.
Distagon (1953) 
Distagon
Asymmetrical wide angle

The “Dista” in Distagon is derived from the word “distance.” Combined with the previously mentioned “-gon” meaning angle, a Distagon is a wide-angle lens with a large distance to the image. A majority of modern Zeiss wide angles are Distagons, including some normal-wides in the 35mm range.

zeissZF
A cutaway of a Zeiss Distagon 21mm f/2.8

Advantages

  1. Compatible with all SLR and DSLR cameras.
  2. Better suited for digital sensors than Biogon designs.
  3. Allows larger apertures.
  4. Minimal spherical aberration and vignetting when stopped down.

Disadvantages

  1. Large in size and heavy in weight
  2. A curved field curvature
  3. Distortions are very difficult to correct and require complex elements
  4. Ultra wide angles have severe coma, chromatic aberration, and distortion.
Hologon (1966)

Hologon

The “Holo-” in Hologon refers to the Greek word “holos” which means “everything” or “complete.” Literally, this is a complete angle extreme wide angle design. Built with only 2 or 3 elements of highly curved and extremely difficult to make glass, Hologon designs are incompatible with today’s flat digital sensors because of an extreme image degradation in the corners.

LS_hologon_linhof-d


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