Introduced in the Spring of 1932, the Contax I was Zeiss's belated response to Leica's cine 35mm based offerings, a rapidly accelerating emerging miniature photography theater that Leica had been totally dominating since 1925 when Leica brought it to life. A close study of what the Contax I was over its brief approximate lifespan betrays a franticness in efforts about its creation. The Contax I has a number of significant decided technical advantages over the Leica that it was to compete with. It has a longer effective rangefinder triangulation base for more accurate focusing. It has a very simple and fast action bayonet lens mount instead of Leica's comparatively tedious screw mount. And, it has a removable back for fast and very positive action film loading contrasted with Leica's awkward skilled effort intensive two blind hole film loading system.

To go up against Leica's horizontal travel fabric focal plane shutter (maximum speed 1/500th), the Contax pitted its vertical travel articulated metal focal plane shutter that is capable of 1/1000th compared to Leica's to speed of 1/500th. It is immune to the normal issues of wear and sun burn through that the Leica fabric curtain is subject to.

Nor was the lens system introduced with the Contax I second best to that from Leica; actually for some available light Sonnar offerings, it was very obviously noticeably superior.

With all of these advantages, why did the Contax I not completely eclipse the Leica offering on its introduction? Stated simply, the Contax I had its own very negative comparisons and problems as well.

Where the Leica body is a solid but relatively light compactly contoured beauty that cradles easily into a user's hands, the Contax is comparatively klutzy, weighs noticeably more, is physically larger and actually feels much larger because of its harsh corners and box-like shape.

From the day that it was first introduced during 1932 to when it was superceeded by the Contax II in 1936 the Contax I was an ongoing work in progress. Various printed works have no fewer than six different variation generations based on obvious external features alone. Additionally there were a great many very significant internal evolutionary beneficial changes such as the location and physical layout of how the angular displacement of the lens couples to the rangefinder system, shown below

or alterations to the shutter curtain transport system to render it more reliable, a very known set of issues at the time. We will apply the accepted version demarcations as set forth by the McKeowns in their 2004 publication:

Version 1: Serial numbers, matched back and body, start with "AU" or "AV" . No low shutter speeds below 1/25th. The front plate corresponding to the focus wheel may have an inverted dimple to accommodate the wheel shaft end. No foot about the tripod socket. Viewfinder window located between the two rangefinder windows yielding the longest possible geometric triangulation base. Front plates covering and surrounding the lens mount and viewfinder and rangefinder windows are fashioned from several separate metal stampings. The distance scale about the lens mount is a casting that is painted black with engraved white numbers.

Version 2: Front plates combined into just one. Dimple gone.

Version 3: Slow speeds added; foot added to tripod socket ; front plate bezel stamping now extended to surround front shutter speed dial as can be seen in the above rangefinder coupling illustrations;

Version 4: Button to release infinity lock added at approximately 1:00 o'clock that is engaged automatically when a telephoto lens is attached. This is not an issue with normal and wide angle lenses as they are focused by the geared focus wheel which has a nearby trivially engaged infinity lock release . This becomes an significant nuisance issue with telephoto lenses which have to be focused by gripping the barrel and turning it as they pose much too great a load for the gear train employed in "three finger operation" focusing the shorter focal lengths. The distance scale is now colored natural nickel with black numbers.

Version 5: Significant internal alteration to the viewfinder and rangefinder layout and system. Viewfinder is now to the left (outside) of the rangefinder. The rangefinder triangular base is now shorter, less accurate but not significantly so.

Version 6: The cast brass accessory shoe now has four screw heads (replacing the previous three) securing it . The marker for set shutter speeds has changed from a small slotted bolt head to a raised polished pointer in the body casting .

It is a mistake to believe that these variations were entirely well ordered and well behaved reflecting Zeiss's preplanned introduction of them. Zeiss, at the time, was preoccupied with efforts to protect its reputation by correcting issues with a buggy 1st efforts product introduction. It is not that unusual to find overlap in the phasing in of the changes.