The Sigriste is well-known for its appearance, range of speeds and unusual shutter. It was also one of the first cameras with a self-capping focal-plane shutter, in addition, the shutter was set by the plate changing mechanism - unusual in a focal-plane camera.

The concept of the Sigriste was a magazine hand-camera, quick to use and possessing high speeds; for this a focal-plane shutter was required. To provide a full range of speeds it was necessary to vary the slit width as well as the speed of travel. A magazine was fitted to the camera, this necessitated that the shutter be self-capping unless a convoluted operating sequence was used. Speed of operation was provided by making the plate changer set the shutter, the one draw back being that the slit width had to be set before operating the changing mechanism.

The Sigriste was available in 9 x 12 cm, 6.5 x 9 cm and 6 x 13 cm stereo sizes. The lens was either a Planar or a Tessar. The patent mentions that an extension can be placed at the front of the camera to take long-focus lenses. Also in the patent is the comment that two shutter speed scales are to be found, one marked in white the other in red, the faster speeds applying when the camera was held upside down.

Shutter Mechanism

The shutter consists of a set of metal plates with a variable separation between them moving across the focal plane. The plates are connected by a pleated-leather sleeve to the lens area which cuts off light except to the shutter plates. The light-tight sleeve is removable.

A large amount of design and production effort has been expended in making the shutter self-capping and tensioned by the changing box. The mechanism may seem overly complicated but in the context of the time it was an advanced design with little else for comparison.

The shutter provides, on this example, 120 settings, but some are duplicated. The slit width has 10 settings between 1 and 10 mm, the speed of travel has 12 settings obtained by varying the tension in a coiled spring.

The slit width is set by moving a lever on the bottom of the camera, this turns a screw (V) attached to one of the shutter plates, increasing or decreasing the slit width. The lever requires two turns to alter the slit by 1 mm, as the lever is turned it also moves a pointer around the edge of the speed dial.

The rate of travel is set by moving an arm on the speed dial, this varies the tension in the coiled spring. The spring is connected to a large wheel inside the camera. The edge of the wheel is grooved to hold a cord (F). The cord is attached at each end to the shutter plates and runs through a loop attached to the wheel. In the untensioned position the plates are at the bottom of the camera, the tension in the spring has rotated the wheel and pulled the cord some way round the wheel. In setting the shutter the plates are moved to the top of the camera which pulls on the cord causing the wheel to rotate back providing the shutter tension.

Setting the shutter

Two hooks (r) at each end of the shutter plates are engaged by the draw of the changing box, as the box is pushed in the end of the box meets the hooks and pushes the shutter plates to the top of the camera.

Release

The shutter is released by pulling back on two triggers situated on the top of the changing box, this pushes pins onto the hooks depressing them and freeing them from the edge of the changing box. The shutter can then move across the focal plane.

Self-capping

If it were not required to be self-capping the mechanism would be straight forward. The shutter plates comprise a top plate (d1) a lower plate (d6) and a closing plate (d3), the arrangement, much simplified, is shown in the accompanying diagram. When unset the plates are at the bottom of the camera, the slit adjustment screw (V) is in contact with its setting lever and can be adjusted. The screw V actually works on a plate behind d6 to which d6 is loosely attached. In setting the shutter the plates are slid to the top of the camera, the lower edge of d3 pushes on d6 to maintain contact with d1. At the start of the exposure the springs r are released allowing the plate d3 to drop, pins on d3 act on d6 and bring that plate down to the extent set by the screw V i.e. the slit width is formed. The shutter is at this point moving across the focal plane. At the end of the exposure d3 strikes the bottom of the camera, d6 also stops when in contact with the lower edge of d3, d1 stops when it strikes d6, thus the slit is closed. Two large springs (k) running from the front of the camera to the shutter plates push down on d1 ensuring contact with d6 except during exposure. Essentially the plates are able to slide relative to each other the slit only being formed during exposure.