Introduction

Motion blur is normally relevant to a film camera - when a frame of the film captures an object that is moving too fast (or the camera is moving too fast), that particular frame is exposed too long to light to '"freeze" the motion of that object and so appears blurry on that frame of film. The amount of motion blur can be controlled in a film camera in two ways:

• by changing the frames per second (fps) of the film so that each frame is exposed for a shorter period of time to the light, thus freezing more and more the action in place. The typical film fps rate is 24fps but can be increased to 60fps or more which will diminish the motion blur and make the movie look more "choppy" - this is usually done for special effects in fast moving action scenes.

• by adapting the angle of the opening in the so called rotary shutter of the film camera. A smaller angle will expose the light for a shorter period of time which will diminish the motion blur. See below for an example of how a rotary shutter works.

Photo camera shutter vs film camera shutter (rotary shutter)

The motion blur settings in Maxwell can be set both for a photo camera and a film camera, so it's important to know how the shutter works in each case to understand the settings.

In a photo camera the shutter simply opens and closes like a curtain to expose the film to light. This speed is determined by the shutter speed parameter in the Maxwell camera. It is denoted as fractions of a second - 1/20 for one 20th of a second, 1/40, 1/250 etc. Setting the camera this way means your shutter will be open for a given period of time, no matter the fps setting of your animation time line.

The shutter on a film camera however is a rotating disc with an opening cut into it, called a rotary shutter, and the angle of this opening determines how long the film is exposed to light as the film rolls by the shutter. Setting the camera this way means the motion blur effect still depends on the fps of your animation because a frame of film can't be exposed longer than the fps setting of the animation, even if the rotary shutter is open during the whole frame. This means an animation running at 60fps will have less of a motion blur effect than one running at the typical film fps of 24.

In the Maxwell camera settings you can pick "Use rotary shutter" and set the shutter angle, by default 180º. Setting the angle smaller means the film will be exposed to light for a shorter time - less motion blur. You can set it all the way to 360º which means effectively there is no shutter blocking the light and the motion blur will be based purely on the frames per second setting of your animation.

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