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The exposure of the rendered image is influenced by the shutter time, f/stop number and film ISO rating. The shutter time and f/stop also influence motion blur (if enabled) and depth of field, respectively. The ISO value acts simply as an intensity multiplier and doesn't alter any other aspects of the output (in a real DSLR, increasing the ISO also increases the electronic noise of the sensor, but Maxwell simulates a "perfect" sensor which does not have this unwanted behavior). To simplify set-up, the plug-in offers 4 exposure modes: manual, aperture priority, shutter priority and rotary shutter.

In manual mode, you can control shutter and f/stop independently, as illustrated in these images:

You can see how going from f/16 to f/8 makes the image brighter, but also produces a more shallow field (more blur). Leaving the f/stop unchanged by increasing the exposure to 1/10 seconds produces a brighter image, but also increases the motion blur on the opening lid.

The priority modes which can be selected from the "Exposure Mode" dropdown allow you to keep the exposure constant while varying either the shutter time or the f/stop, but not both. The exposure is defined by the EV number, a standardized setting found on cameras which also offer priority modes. When using shutter priority, you can change the shutter time to control motion blur and the f/stop is adjusted automatically:

Notice how the two images have equal brightness, but the motion blur is less pronounced when the shutter time is halved. However, since the f/stop is adjusted automatically to keep the exposure constant, lowering the shutter time also produces a more shallow field, as you can see by comparing the blur on the foremost lighter.

The situation is reversed when the priority mode is set to aperture: you can control the f/stop directly and the shutter time is computed.

The brightness is not affected by going from f/18 to f/10, so in this mode you can control the depth of field without affecting exposure. Since in this case the shutter time is slaved to the f/stop, a lower f number also produces shorter exposure, so in the second image there's almost no motion blur.

The fourth mode, rotary shutter, can be configured separately by checking the "Use Rotary Shutter" box. A rotary shutter is a device found on movie cameras which is used to control the shutter time: a semicircular object rotates in front of the film, performing a complete rotation during a frame. The angle of the opening in the shutter determines how long the film is exposed to light: 90 degrees means that the shutter time is a quarter of the frame time, while a value of 360 degrees means there's no shutter at all and the film is exposed for the whole duration of the frame.

In this mode Maxwell overrides the shutter time value input by the user with the value computed from the angle (time = angle / 360 * frame time). It then adjusts the film ISO value so that you get the same exposure as you would with the shutter, f/stop and ISO value that are specified in the camera parameters. This means that you can set up the exposure and depth of field as you would for a still shot and then control the motion blur independently, without affecting anything else in the render.

Observe how turning on rotary shutter leaves the exposure and depth of field unchanged, but allows you to control the motion trails in isolation. This is in contrast with the shutter priority mode, where changing the motion blur also affected the depth of field, and with the manual mode, where changing the blur also changes the image brightness.

Keying the Maxwell Camera Attributes