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Although not a real conundrum or a deeply buried enigma, this question has been asked many times;  indeed, why the 9.2mm format? Is it indeed 9.2mm, or is it 9.3mm, or 9.something ? Which is it ? What were the reasons behind this format being chosen for the Minox cameras? These here are my own thoughts on the matter, or as they say, my 2 cents 🙂 .

First of all, this format is usually mentioned as “9.2mm”, “9.4mm”, “9.5mm” or just “Minox film format”; however, the width of the film negative used in 8×11 subminiature cameras varied and so it does even today. Minox plastic cassettes are more prone to jam if film exceeds 9.2 or 9.3mm. On the other hand, the old metallic cassettes accept widths of 9.2mm to 9.4mm, from my 20-something years experience with Minox format. The inner take-up spool of plastic cassettes has been varying from 50 exposures (first models) to only 15 exposures (modified center take-up, late 70’s, early 80’s), standard film length being that of 36 exposures. The old metallic ones accept 50 exposures, and of course, 36, if so loaded. I can say with certainty that a width of 9.5mm does not work in any Minox cassette, and jams the camera.

Most popular cine film small formats here:

8mm = 4.88 mm x 3.68 mm
Super 8mm = 6.24 mm x 4.22 mm
9.5mm (Pathe) = 8.50 mm x 6.50 mm
16mm = 10.26 mm x 7.49 mm
Super 16mm = 12.35 mm x 7.49 mm

Joseph Cooper says in 1961, in his book (“The New ULTRA-miniature photography”) that the width of Minox film is 9.5mm, while Rolf Kasemeier in his “Small camera, big pictures” mentions the same film as “9.4mm”.

According to Martin Tai of ” Early VEF Minox factory brochure and an advertisement in Switzerland ca 1938, stated that the film used was 9.5 mm unperforated film. That was where all this “9.5mm” film started- by VEF Minox in Riga. By 1939, the statement “9.5mm” had disappeared from VEF Minox advertisment, only “8×11″ format was stated.” And he also says that ” I measured a piece of Copex film slitted from Minox slitter. To prevent film bulging under the pressure of micrometer, I folded the film strip back to back in a loup; the width of the film is 362 mil. 0.362 x 25.4 = 9.1948 mm = 9.2 mm”

Also, a test run on a 1939-1940 VEF film strip measured the width of the negative at 9.33mm to 9.37mm, average being 9.35mm along the strip. Factoring in the variations of the celluloid negative during the years (the test was run around early 2000’s), it would appear that the width could not exceed 9.4mm, as far as I can understand.

In one of his (rare) interviews, Walter Zapp seem to explain the reason of choosing this format, when he designed the Minox. Apparently, the small format was the natural inspiration for him, as it would appear that the 9.something mm was readily available on the market already at that time. Did he ever envisaged using the cine film initially? The cine cameras were using it on a grand scale. As they referred to this format being “moving pictures film negative”, it was the smallest format, and he obviously went for the small size. And the logical source of his choosing this format was the existence on the market of the Baby Pathe film negative of 9.5mm, center perforated. Where did he find the non-perforated 9.5mm is another thing which lies in the shadows. Special order perhaps? I do not know and I do not think he ever used it. Obvious reasons for this assumption, the middle perforation of this popular negative denying the use of it. Was this film an inspiration to cut his own from whatever stock? Probably.

One problem was to find such suitable negative readily available, and most definitely 9.5mm was not available unperforated. Did he ever imagined or indeed used 9.5mm Pathe film negative in his Ur camera? It would seem he did not; he specifically designed the cassette to take 9.4mm film, and in doing so, he denied the producers of 9.5mm cine film to come into Minox courtyard with their product. Even so, knowing that 9.5mm is too wide for Minox cassette to work, how the heck can one cut 0.1mm off the negative, so to end up with 9.4mm ?

So? Well, I guess he did slit his film from either 35mm or 127 format, both immensely popular at the time. My bet would be on 35mm, as it was kind of new thing on the market used for still photography, itself coming from the cine domain. Probably the new emulsions were a plus, which Zapp thought to be better for his new camera. Of course that sort of negative was nothing of the likes we have now, in terms of backing, emulsion, etc. Alas, no clear proof or indication that he really did so. We can only guess with some comfortable degree of certainty.

Also, the brass cassettes VEF produced following Zapp’s plans were indubitably very forgiving, relative to the dimensions of the film strip. I also believe that the entire film housing, advancing mechanism and film gate/lens/cassette were designed with this format already in mind. Initially, the cassettes were probably manufactured with certain higher tolerances, as opposed to the plastic ones which came out in the late 60’s/early 70’s. Said that, it is probably better to deal with a cassette made out of plastic (true, breakable but not prone to temperature variations), instead of metallic ones.

The subsequent habit of film slitting/cutting/splitting probably came as a surprise to Zapp, when it appeared later on in the period, as I do not believe he envisaged this sort of getting Minox cassette reloading. I do not believe the plastic cassettes followed the exact dimensions of the previous metallic ones; better mold injection machinery, materials and fabrication procedures were put together to produce cassettes with more exact dimensions. And I do not believe that the format of the film negative we now use in our cameras is the same one the UR or RIGA used back in the day. There are visibly differences between the height and thickness of the spools, caps, etc. The free movement of a 9.2mm negative strip in an old metallic cassette speaks for itself, for example.

To close things here (for now), you can enjoy a good video footage, showing some of the most important moments of the birth and life of what we know today as the Minox camera.

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