Filmed TV and the Rerun
I Love Lucy, which began in 1951, chose — in an age when live broadcast was the norm — to perform in front of an audience and put it on film. Three cameras. So that the action would not have to stop, the cinematographer Karl Freund built a lighting system that lit the whole set at once from above.
Calling this "the invention of the three-camera setup" may be a little careless, though. The industry body's account says the method carried the practice of live television over into film production, and that other companies were already using it in limited ways at the time. Desi Arnaz wanted it brought over, Freund put the technique together, Marc Daniels directed. Not one person's invention, but the result of a division of labour.
What really mattered in this band was not the number of cameras but the contract. The network wanted a live broadcast from New York; the two of them wanted to stay in Hollywood and shoot on film. The network gave way, but asked in return that they cover the extra production costs themselves and take a cut in their fees. In exchange, their company, Desilu, took the rights to the show outright. Programmes became things that remained, and things that belonged to someone — that is the ground everything after this stands on.
What follows is the part most often misunderstood (see the myth note).
Desilu went on to send out The Untouchables, Mission: Impossible, and Star Trek. The company in those years was led by Lucille Ball — the first woman to head a major American studio. A choice made to keep a live play from vanishing gave rise, a dozen-odd years later, to a story about a starship (→ The Genre Serial).
The myth, corrected
Desi Arnaz took ownership of the film because he foresaw the rerun business, and Desilu went on earning from reruns
Taking ownership is a fact. But the industry body's own account says that syndicating reruns was not yet standard practice, and puts the couple's motive no higher than securing the long-term value of the show by putting it on film. And Desilu did not hold on to it: in October 1956 it sold the rights to CBS for 4.3 million dollars, and used the money to buy the RKO studios for 6.15 million in 1958. The meaning of that ownership was not royalties arriving forever; it was that an asset had been made which could be sold. Incidentally, what made reruns possible was shooting on film and holding the rights, not the fact that there were three cameras.