Industrialized film production in its infancy.
If one was thinking of a career as a "camera operator", as they were called, a good time to get into it was the mid 1910's. By then US film studios on the east and west coast invested heavily in meeting the demand for theatre content.
Audiences generally didn't like to see the same film twice so studios produced films numbering in the hundreds every year. Shorts, newsreels, novelties, and features.
Here is one of the best examples of assembly line film production. Universal City's 700 foot stage where multiple scripts could be shot at the same time. Off in the distance are the sets for The Dumb Girl Of Portici, a big budget feature shot in 1914 and released in 1915.
If this photo looks familiar you probably saw it in the 2017 Silent Movie Calendar. It was picked for March and is an unused, real photograph postcard for purchase at the original Universal City tour.
Three more of these early Universal photographs are in this book. As far as I can tell none have been published anywhere else.
If you haven't already, please pledge on this Kickstarter to see these and much more in the 240 page, fully illustrated "How To Film Moving Pictures in the 1910's."