Red window

In 1892 the red window was introduced by the Boston Camera Manufacturing Company as a means to control film advance of paper-backed rollfilm in the No. 2 Bulls-Eye camera. Later this became the film advance control device of nearly all cameras for the popular rollfilm formats 127 (4cm) , 120 and 620 (6cm). The window shows an exposure number that is printed on the film's backing paper. The appeareance of the next exposure number in the window means that the film is advanced enough for not achieving overlapping exposures. Some cameras use a different color for the exposure counting window, for example the Rollex 20.

Looking behind a 120 film box camera's door: the number visible through the red window is one of the exposure numbers of the eight possible 6×9cm exposures. Other number rows are visible through exp. counting windows of cameras with smaller frame formats for 12 or 16 exposures..

Glossary Terms