The transitions are the cinematic devices by means of which one scene changes gradually to another instead of there being a sudden change, as with a cut. The three basic types of transition are the fade, the dissolve and the wipe.
With a fade the scene either gets progressively darker until it becomes black (a fadeout) or appears out of blackness (a fade-in).
A density wedge, i.e., a neutral filter in which the density increases smoothly and progressively from one end to the other, is sometimes used to obtain fades in the camera: it is slid across in front of the camera lens. The more advanced cameras have a fade shutter-that is, a variable shutter that can be operated while the camera is running and which gradually reduces the exposure to zero for a fade-out, or opens up to full for a fade-in. A cruder method of fading, often used by amateurs, is to close down the lens aperture; but this will only work
If there is a large enough range of aperture atops to produce a full black, and in any case there will be a variation in depth of field.
To be fully effective, a fade with the lens aperture needs an iris diaphragm which can close down fully. The difficult part of making a fade in this way is the timing of the closing down stage so that the darkening of the scene is uniform and gradual. An accessory available for certain cameras closes down the aperture at the uniform rate by a motor.
A number of amateur cine cameras also have a variable shutter and may in certain cases link the control of this with a fading motor.
The dissolve is an effect whereby one scene gradually fades away at the same time as another scene gradually appears and takes its place. To produce a dissolve the first scene is faded out by one of the methods described and the camera stopped. The film is then wound back to the beginning of the fade and the next scene is shot with a fade-in that coincides with the fade-out already there.
A wipe is the type of transition in which a line or shape moves or grows on the screen, gradually wiping away one scene and disclosing the other. In the professional version both scenes are in contact along the line of the wipe and, as it is usually impossible to arrange the necessarily accurate timing with a double exposure in the camera, this transition is a product of the optical printer. The amateur compromises: he wipes away a scene by covering the field of view with a black card cut to the desired shape; there is no winding back and the next scene is uncovered from blackness with a similar shaped card. There is here an affinity with a fade, so the transition is more properly called a wipe-fade.
Various other scene transitions (such as iris fades and wipes where a scene emerges out of a rapidly growing hole in the center of the previous scene) are almost invariably produced by optical means during printing.
A flash-pan is a sudden transition rather like a cut, but conveys the impression as if the camera had rapidly panned from one scene to the other. It is made by concluding a shot with a quick pan away from the subject. This panning movement must be sufficiently rapid to blur the subject beyond recognition. The second scene may be introduced by a similar flash-pan and the two joined up. the middle of the pan. In practice, however, it is sufficient to use only the first panning movement to connect the two scenes.
It is much more difficult to bring the camera to rest without any jerk and exactly aligned on the view it is to take in.