Shutter angle is a term that is commonly used in the context of film cameras and refers to the angle of rotation of a mechanical shutter that is used to expose the film. The shutter angle is typically expressed as a degree measurement, such as 45 degrees, 90 degrees, or 180 degrees.

The shutter angle is related to the duration of time that the film is exposed to light, in the same way that shutter speed is related to the exposure time in digital photography. In film cameras, the shutter consists of a rotating disk or drum with an opening that exposes the film as it rotates past the lens. The length of time that the film is exposed to light is determined by the size of the opening and the speed at which the shutter rotates.

The shutter angle is calculated based on the width of the opening in the shutter and the length of time that the opening is visible during each rotation. For example, a 180-degree shutter angle means that the opening in the shutter is visible for half of each rotation, or 180 degrees of a full circle. This results in a standard exposure time of 1/48th of a second for cameras shooting at 24 frames per second, which is the standard frame rate for most film productions.

The choice of shutter angle has an impact on the look and feel of the final image. A shorter shutter angle, such as 45 degrees, results in a shorter exposure time and a sharper image with less motion blur. A longer shutter angle, such as 270 degrees, results in a longer exposure time and more motion blur, which can be used creatively to create a sense of movement or to give a scene a dreamy or surreal quality.

In summary, shutter angle is a term used in film cameras to describe the angle of rotation of the mechanical shutter that exposes the film. It is calculated based on the size of the opening in the shutter and the length of time that the opening is visible during each rotation. The choice of shutter angle has an impact on the exposure time and the final look of the image, including the amount of motion blur.