I know, I know, citing Citizen Kane may be common place, but it sure has a place in film history. Welles created a new style of filmmaking by combining various forms of movie making into one. The film has many innovative technical aspects through experimentation with lenses and lighting. The extended use of deep focus is one of them. Nearly every scene has the foreground, background and everything in between in sharp focus.
Another innovation was the way low-angle shots were used to achieve a point of view that could show ceilings in the background. Back then, movies were mostly filmed on sound stages and not on location, and it was impossible to film at an angle that showed ceilings because the stages didn't have one. So, Citizen Kane became the first film to show the ceiling of a room.
Also worth notice is the storytelling narrative style. Citizen Kane distances itself from the traditional linear, chronological narrative and tells Kane's story entirely in flashbacks and different points of view. Welles' narrative concept differs from the traditional single storyteller and uses multiple narrators to tell Kane's story, something never before seen in a Hollywood movie until then.
Welles was also a pioneer in visual effects, cheaply shooting things like crowd scenes and large interior spaces, uniting long tracking shots with well disguised wipes and combining sets shots with miniatures. For example, the scene where the camera starts on the outside of a miniature building in a rainy night, making its way through the skylight window (a disguised wipe) and entering a room from the top (something a lot of filmmakers do easily today with CGI).
If you have never seen Citizen Kane, check it out. You'll notice all of the above and much more.
