Frena is a kind of simplest cameras. The body was usually made of pressed cardboard covered with fabrikoid, or plastic in a later period.
The camerascontained the simplest fixed-focus lenses (most often a single-lens Meniscus, a periscope or a landscape lens). The shutter in the box chambers was set in motion by a spring. Exposures were designated by the letters Z (long) and M (instant) and were equal to approximately 1/30 and 1/60 s. The shutter had a trigger.

To determine the frame boundaries in such cameras there were two SLR viewfinders: for vertical and horizontal shots.
Box cameras were designed for the use of photographic plates located in a special storage with a mechanism that could quickly replace them.