One of the main reasons color reversal was used in professional 16mm was the dust problem. Although color negative was available in 35mm in the early 1950s, 16mm color negative camera film wasn't available until the early 1980s (7247 7291). What made this possible was continuous high-speed full submersion "liquid gate" contact printing. 7252, or ECO (Ektachrome Commercial Original), was a very slow-speed film with incredibly low contrast, the log-C of its day. Unlike all other Ektachrome camera films, it was not designed to be directly projected like the Ektachrome EF, MF, and VNF. It was designed to be printed on a higher contrast print stock, allowing you room to print up or down a few stops.