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How it Works:
The Minox Shutter

Rick Oleson

Of all the world’s great camera designs, the Minox is perhaps the most remarkable. Developed in Latvia by a firm that had never produced a camera before, the very first Minox combined shutter speeds from 1/2 to 1/1000, focusing to 8", automatic parallax compensation viewfinder, built-in filters and a 50 exposure roll of film all in a package so small you could carry 8 of them in the space occupied by one Leica M3 without a lens.

As one might expect for this list of credits, the inside of a Minox is a veritable wonderland of mechanical ingenuity, and the story of its origins could easily make a book in itself. But rather than try to stuff a book into one newsletter, I’ll try to confine myself to a single area of the Minox design, the shutter mechanism.

The Minox shutter is a two blade guillotine type, similar in action to a focal plane shutter but located in front of the lens. Its paper-thin stainless steel blades travel horizontally by the force of two tiny extension springs, and- timing is provided by a gear train mechanism tucked into the space above the viewfinder. Both blades are released by a single lever which withdraws two unequal-length pins from the end of the blades. Since both pins move in the same direction, at the same speed and at the same time, the shutter speed is determined by the difference between the lengths of the two pins (which is fixed) and the speed at which the lever moves (which is dependent on the position of the shutter speed dial). When released, the lever draws back far enough to fully withdraw the shorter pin from the opening blade which is pulled across by its coil spring until it comes to rest against a stop bumper. In this position, a rectangular hole in this blade is aligned with a similar hole in the closing blade„ allowing light to enter the lens. The activating lever, meanwhile, has run into the timing mechanism and has been slowed down. Once it has passed through the required delay, the lever proceeds until the longer pin is withdrawn and the second blade travels across. Now the openings in the two blades are no longer aligned and the shutter is closed. The timing mechanism is unusual in a few respects; first, a single gear set of simple design covers all speeds from 1/2 to 1/1000: most shutters require at least two or three gear sets to cover such a wide range. Second, the spring driving the actuating lever is opposed by a weaker one acting directly on the gear set, and both are totally independent of the springs powering the blades themselves. And third, because of this unusual spring arrangement, the timing mechanism literally winds itself back up with its rewinding spring when the camera is closed. Which brings us back to our story.

To re-cock the shutter which has just been released, the camera body is "closed". In this operation, the bumpers which stopped the blades now push them back to the starting position. The actuating lever is also returned to its starting position and the timer rewinds with a faint buzzing sound which lasts for about a second.

Although the triggering and timing mechanisms are now cocked, the shutter springs themselves will be tensioned only when the camera is reopened for the next exposure.

Clever as it is, though, the original Minox design does have its shortcomings. One of these is that the closing action automatically advances the film even if no exposure had been made. And while a non-resettable 50 exposure frame counter was probably fine when Minox film came only on a 50 shot roll, it's a bit inconvenient with today’s 36 exposure loads. Potentially more serious though, is the inherent delicacy of the small parts which make up the mechanism. Spring breakage is a real possibility; and in a device that requires a pair of .001 inch thick blades to be pushed into position, the slightest obstruction can result in total and permanent disaster. Still, it's easy to find a 30 year old Minox still working, and many have survived hard use to become famous tool's of espionage and military intelligence for two generations.

Originally published in The Minox Memo, Spring 2003, Volume 2, Number 2, Series 2.

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