Steve Cushing Impresionist Fine Art Photography

Steve Cushing Impresionist Fine Art Photography

Embracing imperfection, recording emotions, one impression at a time…

Carl Zeiss CZ Flektogon 20 f4.

Stacks Image 55
Stacks Image 57

The Lens details of a series of images taken by Steve Cushing on mirrorless camera.

This History

The Flektogon and its brother the Angénieux retrofocus are the grandfathers of all modern wide-angle lenses, and prior to their invention in 1949, wide-angle lenses for 35mm SLR cameras simply didn’t exist. Their birth can be traced back to the days just after the end of World War II when the very first single-lens Reflex (SLR) pentaprism cameras, such as the Rectaflex and Contax S, hit the market. While SLR cameras would go on to revolutionise photography and become the dominant form of 35mm camera, in the early 1950s their invention created problems for lens designers.

With his invention of the Biogon 35mm f/2.8 lens for the Contax camera in 1934 (reviewed on this site) Ludwig Bertele had shown that lenses with an angle wider than 60 degrees were possible on a 35mm camera. However this type of lens was unsuitable for SLR cameras because they required a much longer flange focal distance (the distance between the lens mounting flange and the film plane). For example, the flange focal distance of a Leica rangefinder of the time was 27.8mm, whereas the flange distance on the Contax S camera was 44.4mm. Wide-angle lenses for SLR cameras required additional space for the internal reflex mirror, and the existing lens designs of the pre-SLR days could potentially hit the SLR’s mirrors, a problem that still exists to this day.

The solution to both problems was solved by two companies at almost the same time, independently from each other, on separate sides of what was then the Iron Curtain. These were the team of Harry Zöllner and Rudolf Solisch at VEB Carl Zeiss Jena in what was then East Germany, and Pierre Angénieux at his own company in Paris. By 1950 they had both applied for patents for 35mm wide-angle lenses for 35mm SLR cameras.

For years lens makers had tried to produce a 35-mm wide-angle for the Exakta but had been stumped by one basic handicap. A lens of conventional design would require a long rear element that would have to penetrate deeply into the camera body, an impossibility with the Exakta because of the mirror. Etablissements Angenieux de Paris solved the problem with a startling idea-inverting the optical system of a telephoto lens so the lens does not penetrate deeply yet provides a short focal length. This idea produced the remarkable 35-mm Retrofocus with a 64° angle of view.” – Angénieux brochure 1952.

While they both solved this dilemma, their methods were quite different. Except for the front meniscus element, Pierre Angénieux’s Retrofocus type R1 35mm f/2.5 was a five element Tessar in three groups, which was pretty standard for the time. Zöllner and Solisch’s solution was a more complicated Biometar type configuration, again increased by the added front element of considerable diameter with a large air distance from the rear elements.

Neither Angénieux, Zöllner nor Solisch cannot be regarded as the inventors of the retro-focus lens, as they based their designs on the principle of the inverted telephoto lens which had been invented in 1931 for cine cameras by Horace W. Lee at Taylor, Taylor & Hobson (GB Patent 355,452 and US Patent 1,955,590). However, they were both simultaneously the first to have created wide-angle lenses for 24×36mm format on 35mm SLR cameras. Because of the limitation of glass technology, coatings, angle of view and the oblique incident rays of light desired, creating wide-angle lenses has always been challenging. Credit must go to these men who achieved their solutions at a time before computer-aided design.

This Lens

The Carl Zeiss Flektogon 20mm 4 followed and the Carl Zeiss Jena 20mm 2.8 was the later successor of this 20mm Flektogon 4.

Why is this lens marked AUS? The Zeiss company was divided between East and West Germany after WWII. The East German plant, located in Jena, could not sell lenses in Western Europe or the U.S. under the Zeiss name, since it was trademarked by the West German division of the company.
The 20mm f4 Flektogon is a wide-angle lens manufactured by Carl Zeiss Jena in East Germany.

Type: wide-angle
Name: Carl Zeiss Jena Flektogon 4/20mm
Coating: Single-coated glass
Focal lenght: 20mm
Maximum aperture: f/4
Minimum aperture: f/22
Quantity of ap. blades: 6
Lens scheme: 7 elements in 6 groups
Closest focusing distance: 0.19m
Filter/attachment size: 77mm


  • Minimal distortion
  • Built quality
  • Ergonomics
  • Lot’s of character

The 20mm 4 Flektogon is famed for the lack of distortion. Architecture and landscape photographers love this lens because lines turn out very straight. I totally agree, the lack of distortion is remarkable – hats of to the engineers at Carl Zeiss Jena for pulling that off. You will not spend time in post production to straighten lines.

Contrast is good and colours are faithful. This Flektogon is also very sharp in the center of the image. The bokeh is also rather interesting and swirly. When you combine these factors and add the lack of sharpness in the corners and the vignetting you can take rather unusual looking pictures which look almost as if you are shooting through an old looking glass. Obviously this is not to everyone’s taste but if you are on the experimental side you will have a lot of fun with the old Carl Zeiss Jena Flektogon.


  • Vignetting
  • Soft in the corner
  • Chromatic aberration

Two major drawbacks (that most super wide angle lenses will have to a certain extent) is vignetting and softness in the corner. Unfortunately the Flektogon 20mm 4 has some major issues here to the point that it can be distracting. The sharpness in the corners is much worse than in the center in the image. In many situations the image does not look harmonious. This even happens when you do not shoot the lens wide open – so it is rather difficult to control it.

On top of the lack of sharpness in the corners, the lens also generates a lot of vignetting. Corners turn out noticeably darker than they should be.

Chromatic aberration is also a slight issue of this lens. Bright lights and reflections are not a favourite of this 20mm lens.


The 20mm Flektogon is still regarded highly for the minimal distortion it produces. It is much appreciated by architecture photographers. Another remarkable feature is the minimum focusing distance of 16 cm, which really allows you to get very close to your subject.

For images using this lens click HERE

For general information on lens design and lens elements go to the homepage HERE


Stacks Image 164

Images with

Site Search

Stacks Image 80
Stacks Image 77

Steve Cushing Photography