Lens Mounts: DKL

WTF DKL?

Never heard of DKL? Well, you’re not alone. DKL is the classification for a family of lens mounts used in a several families of leaf shutter cameras (both SLR and rangefinder). For simplicity’s sake that family of lens mounts will be referred to simply as the DKL mount.

DKL mount specifications

Mount type: Bayonet (lens release on body)
Flange focal distance: 44,7 mm
Film format: 36mm x 24mm (‘Full frame’)
Mount communication: One lever for selected aperture (camera-to-lens); another for aperture stop-down (camera to lens).

History.

Back in the 1950’s it was yet unclear which shutter technology – leaf shutters or focal plane shutters – would ultimately rule the field of professional and prosumer cameras. While both the German and Japanese photographic industry had introduced a number of new marvels based on focal plane shutters, none of the central companies manufacturing leaf shutters were yet ready to give up without a fight.

As a result, both Gauthier (manufacturers of Prontor leaf shutters) and Deckel (manufacturers of Compur leaf shutters) designed their own interchangeable lens mounts that integrated a leaf shutter in the camera-end of the lens mount. Gauthier’s solution is today known as the SLK bayonet, and Deckel’s as the DKL bayonet (you sometimes also find it referred to as the Deckel bayonet or bayonet-compur) ¹.

Deckel approached the field of German camera manufacturers and was able to attract a number of them to adopt the DKL bayonet (the SLK did not fare as well), but although leaf shutters were a mature technology, the ‘leaf shutter integrated in mount’ took some time to settle into a workable solution (initial DKL lenses had aperture rings, later these moved to the camera-end of the mount).

Also, while the first generation of DKL cameras were rangefinders, Deckel saw that reflex cameras were on the rise and developed another implementation suitable for SLR’s ².

Problematically, what had been at one point thought of as a potential “(west) German unified mount” started fragmenting, and various users of the DKL mount started implementing their own proprietary, artificial limitations to limit the interchangeability of interchangeable lenses (pun intended). Therefore, at various times, the Schneider-Kreuznach Xenar 50 mm f/2.8 was available in five non-compatible DKL versions (Balda, Braun Paxette, Edixa, Kodak and Voigtländer Vitessa) ³.

To make matters even worse, some manufacturers even used several mutually non-interoperable versions of the DKL mount (You could not mount a Voigtländer color-skopar 50/2.8 made for the Voigtländer Vitessa on a Voigtländer Bessamatic, instead you had to use a Voigtländer color-skopar 50/2.8 made for the Bessamatic ). A 10-letter word comes to mind, and it starts with ‘cluster’.

And while one could argue that leaf shutters in interchangeable lens reflex cameras were a technological dead-end, during the relatively short lifespan (ca 1957–1963), the line of DKL cameras did produce a few industry first’s such:
• The 1959 Voigtländer Zoomar 36-82 f/2.8 (World’s first production zoom for a 35 mm camera)
• The 1962 Edixa Electronica (first interchangeable lens SLR with full exposure automation)

Today

Indeed, who cares about ancient history, and who could possibly want to use almost 70 year old optics. Well, it turns out that many do. Moreover, as most of the proprietary incompatibilities are relatively easily circumvented (oldskool lens hackers used to do this with diamond files) simply by purchasing a DKL-to-whatever adapter) adapting DKL lenses is by no means as difficult as it may seem.

Finally, there is one very big attractor than can be expressed succinctly by saying: Schneider-Kreuznach, Rodenstock, Voigtländer, Steinheil, Enna.
Because whatever technological failings may have contributed to quickening the infighting-laden demise of the DKL systems, the optics used by DKL cameras were as good as they could be in the 1950’s.

Adapting DKL lenses

Irrespective of whether you want to adapt a DKL lens to an SLR or mirrorless, there are two things to consider: Firstly, the adapter must have been designed so that it allows for controlling the lens’ aperture mechanism. Secondly as the widest lens ever made for the DKL system was a Schneider Curtagon (28mm f/4), you should either be using a full-frame camera (to not incur a crop factor) or be on a mirrorless platform that allows you to use a focal reducer. Thirdly, as the various camera manufacturer did their damnedest to make the various DKL mount incompatible, you may encounter DKL adapters that are not able to adapt all DKL lenses. If you want to make sure, contact the seller in advance and ask about your lens.

Onto SLRs

Technically the flange focal distance of the DKL mount is 44,7 mm and if you’re thinking of adapting DKL lenses to dSLRs, that does not sound promising. But as the DKL lens mount is somewhat unusual, that flange focal distance is not computed from what you would ordinarily think of as the flange (the outermost part of where the lens touches the mount) but from the back-plate of the DKL mount. See pic below:

When you further consider the rather diminutive base of DKL lenses, you’ll notice that they have no trouble fitting into (into, not onto) the mount of most post 1958 proprietary SLR mounts. It is therefore not surprising, that you can find adapters from DKL to all the most popular current SLR mounts ⁴.

Onto mILCs

As usual, and assuming your adapter allows you to control your DKL lens’ aperture, there are very few technical problems to be expected. Furthermore, if sub-full-frame is how you roll, you even have the option of daisy-chaining adapters to include a focal reducer (e.g. MFT-EF focal reducer and EF to DKL adapter with aperture control)

There is one minor detail though: While one would not expect that adapting a lens that has a flange focal distance of 44,7 mm (effectively between Canon EF and Pentax K) to lead to a big adapter, that is a misconception based on the rather unorthodox structure of the DKL mount. In reality, the DKL adapter is huge (see pic below) and can effectively dwarf the smaller DKL lenses.

Identifying the DKL mount?
See more here.

Footnotes

1. Read more here (in german)
2. Leaf shutters in SLRs are a bit of a kludge because the mirror needs to double as focal plane shutter (in the sense that the mirror may not let any light through) and the picture-taking process becomes hideously complex:
   • Photographer frames, focuses etc. (Mirror is down, leaf shutter is open)
   • Photographer pulls trigger (Leaf shutter is closed, mirror is raised)
   • The picture is taken (Leaf shutter opens, closes)
   • Return to normal (Mirror is lowered, leaf shutter opens)
   As one commentator puts it “[Camera] mechanics smilingly turn down repair requests [on such cameras], or turn, run and scream” (my translation)
3. Some details are available here.
4. At the time of writing, DKL adapters were available to at least Canon EF, M42, Nikon F, Pentax K Sony/Minolta A (as well as Leica M).