Praktina IIA

KW Praktina IIA with T 2.8/50 Jena (Tessar)

Interchangeable prism viewfinder with exposure meter

 

Legendary, very advanced camera from the 1950ties, often called the first "system camera", and that's certainly true. The camera is like an open system, you can change lenses, viewers, viewerscreens, you can mount motor drives for the film advance, long film magazines and loupes for the prism finders. And the prototype, just called "Praktina", was introduced at the Photokina in Cologne already in 1952! Serial production started in 1953 with the Praktina FX, in 1958 it was replaced by the Praktina IIA, which was even more advanced.

 

It is hard to describe all the progress, that camera brought. For example, you have a shutter speed dial for fast and slow shutter speeds combined, you can turn it in any direction without stop, with the shutter tensioned or not. The shutter speeds are equidistant on the dial, and when the shutter runs, there are no rotating parts outside the camera - sensational.

 

So I picked out two technical highlights:

Since 1954 the camera was equipped with an automatic aperture. It worked like the one on the Contax SLR with M42 mount: the aperture is open for viewing, but when the shutter button is pressed, the camera pushes a pin into the lens and the diaphragm will close to the value selected on the f-stop ring. With the introduction of the Praktina IIA there was change: the new camera pressed the pin permanently into the lens to keep the diaphragm open for viewing. When the shutter button was pressed, the camera *releases* the pin, the aperture was closed by a spring force in the lens. This concept was used at first in the medium format camera "Praktisix" (later Pentacon Six), and since both cameras Praktisix and Praktina were developed very close to each other, the Praktina was the first 35 mm SLR with that design. Nearly every great manufacturer of 35 mm SLR used it, until Canon introduced the EF mount and the the diaphragm was operated electronically.

Perhaps you've noticed, that I'm presenting the IIA with an unmounted lens, and furthermore, that there are some springs and levers too much in the mirror box. The reason for that device is to keep compatibility with the - let me call them - FX-lenses. IIA-lenses are mounted commonly with the indexes on top, using the kerf on top of the camera mount (under the "IIA"). FX-lenses are mounted turned, they must use the kerf beside the self-timer. About 3,000 to 4,000 IIA-cameras were modified that way by the manufacturer itself.

 

The second highlight is the shutter introduced with the IIA. When thinking of the movement of a horizontally traveling shutter with curtains made of cloth, you certainly imagine a slot with a constant width traveling in front of the film (at fast shutter speeds). That's not the entire truth: the curtains are moving accelerated, so the first curtain is *earlier faster*. As a result the width of the slot increases during the exposure. Now you might expect an uneven exposure along the frame, but the effect can compensate itself. A slowly traveling narrow slot can produce the same outcome like a fast traveling broad one, but an exact compensation was certainly random. I don't know if early camera designers knew about that effect, but after WWII there were new technical instruments you could examine it very precisely. So, the designer of the Praktina, Siegfried Böhm, was the first one who could control that effect, the increasing width of the slot was exactly compensated by the speed of the shutter curtains. He used rolls for the curtains with a specified diameter, thus the shutter movement was also less dependent from the spring force of that rolls.

 

Unfortunately the production of the Praktina was ceased in 1960, it was a directive of "decision makers". A pretext could have been, that two lens mounts were sufficient (M42 and Exakta), and it was too expensive to produce lenses in three versions.

 

See excellent articles on zeissikonveb.de and dresdner-kameras.de (in German)

Done