Universal Camera does not update when Focal Distance is changed?
Posted by Joseph Drust on 08 March 2019 08:42 AM
The Universal Camera does not update when the Focal Distance is changed?

This is related to the 'AC' or Auto Crop mode.

Auto Crop mode

1. When located outside the model’s camera boundary (a spherical perimeter), the Universal Camera functions as a true camera.

2. When the camera gets too close to the model it will trigger a 2D Zoom factor to simulate a true Zoom 3D. This step is very similar to the camera crop factor found in multiple DSLR cameras.

This switch between modes is done to avoid camera deformation and unexpected navigation issues.

Because of this Zoom process, when the camera is brought too close to the model and requires zooming in “2D”, the camera will no longer update perspective to match a physical camera.

To help you know when ZBrush switches from a physical camera to a virtual camera with this zoom operation, you will see a change in the “AC” indicator at the top of the screen. This “AC” stands for “Auto Crop”:

    • Grey: the camera is in true perspective
    • White: the camera is using true perspective with a 2D zoom applied — the Auto Crop state.

The AC Mode indicator, on and off.

There are several factors that contribute to the bounding perimeter at which AC mode can kick in. These include camera settings and your model’s volume in the 3D space. Because the model bounding perimeter used by the camera is spherical, a wide-yet-flat model will have a large spherical bounding perimeter, more quickly triggering this AC mode. Also, a wide angle camera (18 or 24 mm camera) will display more of the model on the screen, making you feel as if you are far from the model even if you are, in fact, close to it.

More information on the ZBrush Universal camera can be found here:

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