Patent History

PATENT HISTORY – Part One: The Rondinax 60 and Rondinax 35U

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The original patents, covering the invention of the Rondinax tanks, I traced from the British patent number on the British-manufactured version of the 35U, the Essex 35 mm. I would guess that the inventors first applied for their patents in Germany and then followed up those applications on other key countries, as is still the case.

So, I am working here entirely from the British patents but I hope that somebody reading this will contact me with information on the patent and manufacturing history in Germany.

The first patent (466276) was granted on 25 May 1937; the date of application was 25 November 1935. It is entitled, Daylight Developing Tank for Photographic Roll Films, and the first two paragraphs read:

We, Michael Lesjak, of Ob Krenz F360, Augsburg, Germany, and Wilhelm Kehr, of 8, Henrichstrasse, both German Citizens, do hereby declare the nature of this invention and in what manner the same is to be performed, to be particularly described and ascertained in and by the following statements:—

This invention relates to a daylight developing tank for photographic roll films, having protective paper strips. The construction is such that the film can be introduced into the tank in daylight or bright artificial light, unrolled by withdrawing the protecting paper, developed, fixed and washed.

I do not know if Lejak and Kehr were employees of Agfa, the manufacturers. Then, as now, the private addresses of inventors are shown on patents. Employers usually have, by right, the power of requiring the patents granted to employees be assigned to the employer. I hope somebody in Germany with knowledge of this matter can add more information.

The patent goes on to describe the key features of the Rondinax 60 (for size 20 roll films like 120 and 620):

In this invention, the film is first led into a preliminary chamber by lateral withdrawal of the protecting paper from the tank after it has been closed. This chamber can itself by made light-tight by means of a rotating shutter, and is so arranged that the developer cannot enter it. A band to which the end of the film is attached before closing the tank is fixed on the common axle of two oppositely placed spirally grooved discs. By rotating a handle operated from the outside, the film is led over a guide into the spiral grooves and so enters the developing tank, which is charged to the appropriate level with developer. In contradistinction to the known methods, the film is led into the grooves from the inner end of the spiral outwards. This method of unrolling the film has a number of advantages. The film can be led into a tank already charged with developer, thereby ensuring uniform contact with the fluid, and absence of air bubbles and flecks. After unrolling, while the film is being developed, it can be continually rotated, so that a uniform development free from flecks is produced. The coated side of the film is is not brought into contact with edges or angles which might scratch it, during the unrolling or developing. The unrolling itself proceeds steadily and without encountering any obstacle. Relatively little developer is required since owing to the vertical arrangement of the spirally-groove discs the tank need only be about half full. The tank is relatively small and compact, and is adapted for travelling. The tank is preferably made of pressed material, for example the artificial resin known as “Bakelite”, or the like.

The accompanying diagram, shown below, shows the operation of the Rondinax 60.

There were, therefore, three key elements to the invention. The first was the separation of the film and backing paper as the latter was pulled through a slit, together with the enclosure of the separated film in a light-tight chamber that could be opened and closed. This elegant solution depends on the fact that the film and backing paper are only stuck together at one end – the beginning of the film – and at the end of film the curl of the film away from the backing paper leads it naturally into the light-tight container. The second was filling the spiral reel from the inside using the film guide to feed the film into the grooves. The third was having the reel horizontal, which halved the volume of developer required.

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The second patent (466319) (Daylight Developing Tank for Photographic Roll Films) was divided from the first application and was granted on the same date to the same inventors. This was the Rondinax 35 for 35 mm film. In fact, it covered the Rondinax 35U since there was provision of a key to open proprietary labyrinthine cassettes made by Leica and Zeiss for the Contax. The key difference is, of course, that the problem was simpler since there is no backing paper. The film is led from the cassette into the spiral reel as in the Rondinax 60. Since it is fastened at one end into the cassette, a knife, operated from the outside, cuts the film so that the entire length can be led into the reel.

The complication for the inventors was that 35 mm cassettes were not standard. Leica, Kodak and Zeiss (Contax) had different designs. The Leica and Contax cassettes were opened and closed by means of a key in the end. The tank, therefore, had to have a mechanism to open these cassettes from the outside. Such a mechanism formed part of the patent. That clever bit is now obsolete and ordinary standard cassettes do not need any manipulation within the tank to open them. The Rondinax 35 must have been earlier or at the same time as the 35U as a simple version for what were to become standard cassettes.

The diagram from the patent is shown below. It can be seen that the position and direction of travel of the knife was changed in the production Rondinax 35U.

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But that is not the whole story. There were other patents from this team, one of which became the Rondix 35. Other patents were not developed into products, more is the pity in one case. The Rondix and the other patents I will cover in another article. I will also cover the British-manufactured Essex 35 and Kent 20 which were covered by the same patents as the Rondinax 35 and the Rondinax 60.

Other aspects of the Rondinax series were covered by a number of German patents. These can be found on Espacenet and searching for Michael Lesjak. Some of these inventions were included in the Rondinax tanks that were manufactured while others did not.

PATENT HISTORY – Part Two: The Rondix 35

The brilliantly simple Agfa Rondix tank for 35 mm film was covered by British Patent 703732 entitled, A Process and Apparatus for the Development of Photographic Roll Films in Daylight. The application was made in Germany on 25 November 1950 and the Patent was accepted and published on 10 February 1954.

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One of the inventors, Wilhelm Kehr, is the co-inventor of the Rondinax patents of the 1930s. The other is Rudolf Strauss, ‘a British Subject, of 3, Hurst Close, London NW11, England’. Again I do not know whether Kehr was an Agfa employee. I think I have identified who Rudolf Strauss was but I need to do more checking.

The patent states:

The present observation is based on the surprising finding that it is possible to dispense with all these parts, as for example lead strap, guide member and spirally grooved discs and yet to obtain unobjectionable development, fixing and washing of the film.

According to the process of this invention the exposed film, on a roll film spool or in a cassette, is introduced into a container which can be closed in a light-tight manner, the beginning of the film being attached to a rotatable core mounted within the container and actuated from the exterior and, after closing the container, the film, or that part of it which is to be treated, is wound in a spiral on the core within the container and subjected to the required treatment while being repeatedly wound on and unwound from the core, with the film upon it, backwards and forwards with a change of direction of the film spiral so that in one direction the film is wound with the emulsion side outside. Advantageously, the film is wound on the core in the first place with the emulsion side facing outwards…

…There are preferably provided on the interior container wall and on the interior of the cover, ribs which are so located that a film coming into contact therefore does so only on its perforated edges.

This is the accompanying diagram:

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Certain features like a frame counter and clamp to hold the cassette end of the film were not included in the production Rondix.

Curiously, an almost identical patent was registered in Canada (CA 533907) on 27 November 1956. It is entitled, Process and Apparatus for Daylight Developing, Fixing and Washing of Light Sensitive Film Strips. The first diagram is identical to that in the British Patent. However, the inventor is shown as Michael Lesjak (deceased), the co-inventor with Kehr of the Rondinax tanks. I do not understand why, if the wish was to protect intellectual property in Canada, the same inventors were not listed in the application.

However, that is the Rondix patent. In the next addition I shall consider patents that describe improvements and extension of the ideas incorporated in the Rondinax and Rondix tanks that never made it to manufacture.

PATENT HISTORY – Part Three: Developed But Not Manufactured

British Patent 700954 entitled, Daylight Developing Tank for Photographic Roll Films with Protective Paper Strips, was granted on 16 December 1953. As with the patent covering the Rondix tank, the inventors are given as Wilhelm Kehr and Rudolf Strauss.

This is essentially a Rondix ‘60’ for 120 film. However, instead of using the principle of the light-tight container used in the Rondinax 60, the inventors devised a method of attaching the film to the central core while pulling on the backing paper. The separation of film is similar to the Rondinax 60 but instead of entering a separate chamber it is led by a guide to a clip on the core which closes automatically. Operation is the then the same as the Rondix, first winding the film in one direction and then the other until development is complete. Various devices were incorporated to let the guide drop away after the film had been wound into the tank as well as a clamp to grip the end of the film near the spool (the latter it was pointed out was not really necessary because the film was held by the adhesive strip to the backing paper).

So this is one that never saw the light of day in terms of manufacture. My guess is that because the Rondinax 60 was well established, a Rondix 60 with the added mechanical complications outlined would not have been an economic proposition. I suppose a Rondix 60 based on the light-tight separated film container of the Rondinax 60 and the spiral-less principle of the Rondix 35 was not adopted because of the problem of grasping the free end of the film as it emerged from the container.

Catching the end of a 35 mm by the final sprockets (obviously not possible with sprocket-free 120 film) was the subject of a British Patent (723276, Photographic Daylight Developing Tank for Roll Film) granted to Kehr and Strauss on 2 February 1955 for an improvement to the Rondix 35. It must be remembered that Agfa had invented its own cassette system for the Agfa Karat series of 35 mm cameras. The film was not attached to the cassette and instead of a take-up spool and rewind knob, the film simply passed from one cassette across the film plane into another cassette. Essentially, Agfa treated 35 mm like roll film. This system was further developed into the Agfa Rapid cassette system which appeared in 1964. Therefore, on the face of it, the Rondix 35 was unsuitable for Agfa’s own cameras since its use apparently depended on the film being fastened to the spool of a conventional cassette. This patent was clearly intended to allow the development of a new Rondix tank that would catch the end of the film emerging from Karat and Rapid cassettes and allow normal Rondix-style winding during development. It was not manufactured and the instruction manual of the Rondix I have at the moment give a method of using these cassettes where the end of the film is not clamped. It involves counting a certain number of revolutions one way and then the other, and so on. Whether I would trust myself to concentrate on counting too and fro for the times it takes to develop and fix a film is another matter.

So that’s another one that was never manufactured.

The final patent (British Patent 705931, Daylight Developing Tank for Photographic Roll Films) granted to Kehr, Lesjak and Strauss on 24 March 1954 provided the basis for film widths other than 120 and 35 mm within a single tank. They describe several methods by which the spiral discs could be moved inwards for, say 127 film, as in a conventional universal tank, while keeping the film guide, clip and strap of the Rondinax tanks central.

Such a tank that would have taken 127 film as well as 120 would have been a valuable addition to the range. A daylight-loading 127 film tank would have filled a significant gap in the market. I really missed not having such a tank, Rondinax 6040 let’s call it, and I suspect many others would have wanted to buy one not only for the 127 films from existing cameras but for such gems as the Rolleiflex 4×4 and its near clones.

Therefore, we have three pieces of 1950s intellectual property from the original team of Kehr and Lesjak plus Rudolf Strauss that were never exploited. The Rondix 35 though did make it to the market, and it is a gem that deserves wider recognition.


10 thoughts on “Patent History”

  1. Lyscanthrope said:

    The link to the full patent of the rondix is there :;jsessionid=ghlZkvb2-WZPk7R0SbSS3imy.espacenet_levelx_prod_2?CC=GB&NR=703732A&KC=A&FT=D&ND=&date=19540210&DB=&&locale=en_EP

    As stated on your youtube channel, I would be interrested in checking if the redesign of the rondix could be possible (using a 3D printer for exemple).

    It doesn’t seem that complex…. but I don’t own a rondix by myself.
    Do you think it may be able (if that is not too much of work) to make a detailed post on the rondix ?
    I mean structural wise :
    – Schematic with dimensions of the different parts
    – Several pictures (even If I think it will have to be redesigned) in order to grasp way it interact

    The key parts (from my view) are :
    – The core (a kind of roller with a clamping device)
    – The tank (well ….pretty simple execept the fact that it have to be light tight and the inlet for liquid : detailed picture of this could be interresting)
    – The canister rest and the path a film will follow when going out of the canister
    – The level to which the liquid goes to (lower to the core, higher …and so)

    For the moment I do not have any idea on own to make the handle of the core liquid tight 😉

    If I have forgoten any key part does not hesitate to add some !

    • Will do something but it will take a while. Not easy to show the detail because of photographing black plastic parts. If you reply by saying where you are in the world, somebody following this blog may be able to lend you a Rondix so that you could start from there.

      • Lyscanthrope said:

        Thank you very much for your answer. I understand that It may be pretty hard to take good picture of it. It will be perhaps more efficient that I send you a proposal model, and you will tell me if you see major differences (non working differences ;)) between the rondix 35 and this model.

        I’ll try to work on a draft model this week end and I’ll send you a link to it.

        I’ve got no idea if that’ll work …. but being able to build new rondix-like would be great for user (and for fun ^^)

        btw i’m from france

  2. Any updates on the “new” rondinax you were thinking of making? I’m sure there would be a few people interested in one., including me! Imagine if a motor could be attached to the turning handle… makes it even easier than it already seems to be.

  3. Concerning the “Rondix” patent, an almost identical patent was issued in the USA (US2769381) on Nov 6 1956. Here too, the inventor is shown as Micheal Lesjak (Deceased), Viktoria Babette Lesjak (Executrix). I noted that the British Pat & US Pat were respectively filled on November 14 & 19 1951. I also found another patent by Lesjak, US271693 filled on August 23 1952 (priority date Sept 20 1951) which is claimed to be an improvement of the device described in patent US2769381.


  4. The ‘improved’ Rondix (never manufactured) was obviously designed to use the short lengths of films in the Agfa Rapid cassette (follower on from the Karat cassette) in which the film was not held at one end, unlike the standard 35 mm cassette. The Rondix instructions describes how to use Rapid cassettes – count the number of turns left and then right etc – but is obviously unsatisfactory because if you lose count the entire film winds round the central bobbin and is ruined. The ‘improved’ version is designed to catch the end of the film and hold it firmly as it comes out of the Rapid or Karat cassette. Unless a use of these old cassettes/cameras, it is a problem which has gone away.

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