What is a deep focus lens?

Depth focusing is a photography and film technology that uses a large depth of field. Depth of field is the range of focal length before and after the image, or how sharp and clear it is. In depth focus, the foreground, the middle scene and the background are all in focus.

When using deep focus, filmmakers usually combine it with deep space (also called deep stage). Deep space is a part of the scene layout, and important actors and props are placed on different planes of the picture. Directors and photographers often use deep space instead of deep focus, which is either an artistic choice or because they don't have the resources to create a deep focus appearance, or both.

The director may only use depth focus in some scenes or even in some shots. Other directors choose to use it consistently throughout the film, either as a style choice or because they think it is more representative of reality.

Producers such as Akira Kurosawa, stanley kubrick, Kenji Mizoguchi, orson welles, Masahiro Shinoda, Aquino, terry gilliam, jean renoir, jacques tati, JamesWongHowe and Greg Toland all adopted Deep Jiaozuo as part of their signature style.

For French film critic andre bazan, the visual style of deep focus is the core of his film realism theory. He elaborated on the role of deep focus in the scene of Wyler's The Best Time of Our Life:

The action in the foreground is secondary, although it is interesting and strange enough to require our close attention, because it occupies a special position and surface on the screen. Paradoxically, the real action, at this precise moment, constitutes the turning point of the story, which is almost secretly unfolded at the back of the room-a small rectangle in the left corner of the screen ... so the audience actively participates in the drama planned by the director.

Focal diopter

In the1970s, directors often used defocused diopters. With the invention, one plane can be focused on one part of the image, and different planes can be focused on the other half of the image. This was and is very useful for the distorted widescreen format with small depth of field.

The splitting diopter is a semi-convex lens, which is attached to the main lens of the camera to make half the lens nearsighted. The lens can focus on the plane in the background and the diopter in the foreground. Separating diopters does not produce true depth focus, but only produces this illusion.

Different from the traditional deep focus, it has no continuous depth of field from foreground to background; The space between two sharp objects is out of focus. Because defocusing diopters cover only half of the lens, lenses using them are characterized by blurred lines between the two focusing planes.

Manipulating depth focus is not a new phenomenon, because it was also created in other ways in the golden age of the 20th century. The diopter provides an opportunity for spectacular deep focus composition, otherwise it is impossible. In the new American wave, director Brian Depalma and other films in the 1970s, such as robert wise's Andromeda and Star Trek: The Movie, extensively explored the possibility of defocusing diopter.