a major step forward to mass marketing of the tlr came with the rolleicord and then rolleiflex in 1929, developed by franke & heidecke in germany. the rolleiflex was widely imitated and copied and most mass-market tlr cameras owe much to its design. it is said that reinhold heidecke had the inspiration for the rollei tlrs whilst undertaking photography of enemy lines from the german trenches in 1916, when a periscopic approach to focusing and taking photos radically reduced the risk to the photographer from sniper fire.