When shooting began on 9 May 1962, Eugene Walter recalled Fellini taking "a little piece of brown paper tape" and sticking it near the viewfinder of the camera. Written on it was Ricordati che è un film comico ("Remember that this is a comic film"). 8½ was filmed in the spherical cinematographic process, using 35-millimeter film, and exhibited with an aspect ratio of 1.85:1.
As with most Italian films of this period, the sound was entirely dubbed in afterwards; following a technique dear to Fellini, many lines of the dialogue were written only during post production, while the actors on the set mouthed random lines. Otto e mezzo marks the first time that actress Claudia Cardinale was allowed to dub her own dialogue; previously her voice was thought to be too throaty and, coupled with her Tunisian accent, was considered undesirable.
In September 1962, Fellini shot the end of the film as initially written: Guido and his wife sit together in the restaurant car of a train bound for Rome. Lost in thought, Guido looks up to see all the characters of his film smiling ambiguously at him as the train enters a tunnel. Fellini then shot an alternative ending set around the spaceship on the beach at dusk but with the intention of using the scenes as a trailer for promotional purposes only. In the documentary Fellini: I'm a Born Liar, co-scriptwriter Tullio Pinelli explains how he warned Fellini to abandon the train sequence with its implicit theme of suicide for an upbeat ending. Fellini accepted the advice, using the alternate beach sequence as a more harmonious and exuberant finale.