Data sheet: Carl Zeiss Jena Prakticar (Flektogon) 20 mm f/2.8

Pekka Buttler, 09/2022


The table below summarizes the lens’ key specifications (measurements based on pictured sample):

Brand:Carl Zeiss JenaLens namePrakticar 1:2.8 f=20mm MC
Focal length(s)120 mmAngle-of-view294 °
Maximum Aperturef/2.8In Production1978–1991
Lens mountsPraktica BSubfamily (if applicable)––
Length347,6 mmDiameter471,4 mm
Filter ring diameter67 mmWeight329 grams
Lens element count9Lens group count8
Aperture blades (S/R/C)56 SFocus throw270 °
Minimum focusing distance19 cmsMaximum magnification1:7,4
Has manual aperture ringYESHas Manual focus ringYES

Further notes:
• Prakticar is the name given to all Carl Zeiss Jena and Pentacon (and many other) lenses designed for the Praktica B mount. Hence, while the lens’ name ring says Prakticar, the lens is a member of the Flektogon family and is optically identical to the 20 mm f/2.8 Flektogon in M42 mount.
• Alike all Praktica B mount lenses, this lens has three electronic contacts that it uses to communicate selected aperture to the camera body and a physical aperture stop-down lever.
• The 20/2.8 Prakticar(Flektogon) is the last new development that Carl Zeiss Jena offered in the Flektogon family. While it is by no means an especially bulky lens, it still has the overall – broadening towards the front – design of early ultra-wide angles.

History of Carl Zeiss Jena

There are few names in camera optics more illustrious than that of Carl Zeiss. The company was founded in the German town of Jena in 1846 by Carl Zeiß (hence: ‘Carl Zeiss Jena‘). During 1846–1945 there are few major developments in lens optics that the company was not involved in. Names that are even today well-known in optics – such as Planar (1896), Tessar (1902), Sonnar (1929), and Biotar (1939) (as well as many names that only optics-buffs know) – were the product of Zeiss’ first century of technological innovation.

After the Second World War Germany was divided into a Soviet zone (subsequently: East Germany) and the west-allied zones (subsequently: West Germany). While the Zeiss works resided in Jena (optics and glasses) and Dresden (cameras), which were in the Soviet sector, a contingent of Zeiss managers decided to move west and ended up setiting up shop in the small town of Oberkochen in the American sector under the name of Opton Optische Werke Oberkochen GmbH. As the relations between the former allied deteriorated and the split into East and West Germany became all the more real, the Oberkochen works changed their name first to Zeiss-Opton and later to Carl Zeiss.

What ensued was a lengthy international trademark dispute with both Zeiss’ (Jena and Oberkochen) laying claim to the name ‘Carl Zeiss’. The resulting stalemate – emblematic of the Cold War in its entirety – resulted in that Carl Zeiss Opton was allowed to use the name Carl Zeiss in the West, but had to use the Opton brand in the East bloc, whereas Carl Zeiss Jena was the only real Carl Zeiss as far as the east bloc was concerned, but could – mostly – not use the Carl Zeiss -name for exports to the West6. The fact remains however, that – starting in 1946 from a shared base – Jena and Oberkochen developed as two independent companies for more than 40 years. After German reunification also Zeiss East and Zeiss West were united again, and have since again been at the undoubtable forefront of lens development.

This lens harkens to the time of the cold-war and the East/West split. During the entire Cold War period, VEB Carl Zeiss Jena was seen by the country’s leadership both as a paragon of the East German technology industry and a showcase of the socialist/communist system as well as a major source of exports (and hence, western currencies). Within the centrally directed economy’s hierarchy, Carl Zeiss Jena therefore had a more prestigious role than other East German optics manufacturers (prominently Meyer-Optik Görlitz and, later, Pentacon), meaning that Carl Zeiss Jena received privileged access to tools and materiel (including the first computer in East Germany) and that its products were always considered the premium alternative.

History of the Flektogon designs

Carl Zeiss Jena was a central player in the development of a class of lenses today known as retro focus lenses (a.k.a. reversed tele focus) – a key approach to allowing the manufacture of wide-angle SLR lenses. While the jury is out on whether Angenieux (France) or Carl Zeiss Jena actually was the first company to bring the concept into production, it is evident that Carl Zeiss Jena was both genuinely innovative and prolific in this niche.

The ‘family name’ of Carl Zeiss Jena’s retro focus wide-angle lenses was ‘Flektogon’ (Carl Zeiss West called its corresponding family ‘Distagon’). The Flektogon family contained lenses with focal lengths of 20, 25 and 35 mm (for 135 film) and 50 and 65 mm (for 6×6 medium format).

• The 20 mm f/4 Flektogon (introduced 1961, manufactured 1961–1975) was on its introduction the widest angle rectilinear retro focus lens ever produced. It was mass-produced in Exakta and M42 mounts as well as in small batches for other mounts such as the Praktina
• It was replaced 1975 by the 20 mm f/2.8 Flektogon, which was only introduced for the M42 mount. This lens remained in production until the reunification of the two Germanys.
• After the 1978 introduction of the Praktica bayonet cameras, a version of the 20 mm f/2.8 Flektogon was made for Praktica B-mount and sold under the name Prakticar 20 mm f/2.8 (This lens). That lens is optically identical to the M42 version.


During the production run of this lens, no significant variants were designed.


This lens cannot be used natively on any current SLR or dSLRs. To use it in its native environment, you will need a Praktica B mount film body. Luckily there are a lot of those available, and many of them are still in perfect working order.

Thanks to being a fully manual lens (manual aperture, manual focus), the lens can be adapted to all mirrorless cameras using a suitable adapter. Moreover, Praktica B lenses are so uncomplicated that a simple ‘dumb adapter’ will do the job perfectly (The electronic contacts communicate only from the lens to the camera and do not impinge on adapting). However, due to that the Praktica B mount never was so successful, one should not expect special adapters (helicoid adapters, tilt/shift adapters) to be easily available. Alternatively, one can choose to daisy-chain adapters (e.g. Praktica B->Canon EF; Canon EF –> mirrorless) which not only opens up possibilities for special adapters, but also allows using speed boosters for those photographers that use smaller than full-frame sensors.

Using Praktica B lenses on dSLRs can also be an easy option, depending on which dSLR.
• Canon EF has the shortest flange focal distance among full-frame dSLR’s and Canon’s wide range of dSLRs are able to mount Praktica B lenses perfectly using a suitable adapter ring.
• With other dSLR mounts (Minolta/Sony A; Pentax K; Nikon F) the relationship between flange focal differences becomes an issue, leading to that adapting will necessitate an adapter that uses corrective optics to allow reaching infinity focus


1 Focal length is (unless stated otherwise) given in absolute terms, and not in Full-frame equivalent. For an understanding of whether the lens is wide/tele, see ‘Angle-of-view’.

2 Picture angle is given in degrees (based on manufacturers’ specs) and concerns the diagonal picture angle. Rule of thumb:
> 90 ° ==> Ultra-wide-angle
70–90 ° ==> Wide-angle
50–70 ° ==> Moderate wide-angle
40–50 ° ==> ‘Standard’ or ‘normal’ lens
20–40 ° ==> Short tele lens
10-20 ° ==> Tele lens
5-10 ° ==> Long tele lens
< 5 ° ==> Ultra-tele lens

3 Length is given from the mount flange to the front of lens at infinity.

4 Diameter excludes protrusions such as rabbit ears or stop-down levers.

5 S=straight; R=rounded; C=(almost)circular at all apertures.

6 Online one can find many lengthy and heated disputes stating that only Jena/Oberkochen is the true Carl Zeiss. While many of these discussions are riddled with misconceptions and a poor grasp of facts and timings, they largely also tend to be tainted by ideologies. Those discussions that focus on claims of one or the other Zeiss not really having rights to using designs developed at pre-war Zeiss are especially ludicrous because after the war practically the entire patent catalogue of pre-war German patents was given freely to everyone (the allied saw this as a form of reparations), hence also kickstarting the Japanese optics industry’s ascendancy (the Japanese optics companies were the most avid users of German optics patents).