Focal-plane Shutter - The Revolving Drum Focal-plane Shutter

The Revolving Drum Focal-plane Shutter

The revolving drum is an unusual FP shutter that has been used in several specialized panoramic cameras such as the Panon Widelux (1959, Japan) and KMZ Horizont (1968, Soviet Union). Instead of using an extremely short focal length (wide-angle) lens to achieve an extra wide field of view, these cameras have a medium-wide lens encapsulated in a drum with a rear vertical slit. As the entire drum is horizontally pivoted on the lens's nodal point, the slit wipes an extra wide aspect image onto film held against a curved focal plane. The Widelux produced a 140° wide image in a 24×59 mm frame on 135 film with a Lux 26mm f/2.8 lens and controlled shutter speed by varying rotation speed on a fixed slit width.

In the Kodak Cirkut (1907, USA) and Globus Globuscope (1981, USA) cameras, the entire camera and lens revolved as the film was pulled past the slit in the opposite direction. The Globuscope produced a 360° angle of view image in a 24×160 mm frame on 135 film with a 25 mm lens and had adjustable slit width with a constant rotation speed.

Revolving FP shutters produce images with unusual distortion where the image center seems to bulge toward the viewer, while the periphery appears to curve away, because the lens's field of view changes as it swivels. This distortion will disappear if the photograph is mounted on a circularly curved support and viewed with the eye at the center. Revolving shutters must also rotate smoothly; otherwise uneven exposure will result in ugly vertical banding in the image. Since the rotation may take several seconds to complete, no matter the shutter speed, the camera should be tripod mounted. For the same reason, flash cannot be used with these cameras.

These cameras are often used for photographing large groups of people (e.g. the 'school' photograph). For this purpose the subjects are arranged in a shortened semicircle with the camera at the centre such that all the subjects are the same distance from the camera and facing the camera. Once the exposure is made and processed, the panoramic print shows everyone in a straight line facing in the same direction. The distortion present in the background betrays the technique.