When working with 3D models, ZBrush has three camera modes – one orthographic and two perspective.
If the Draw > Perspective switch is turned off then ZBrush is in Orthographic mode. This means that there is no distortion of the model and parts that are near to the viewer are the same size as parts that are further away. This is a good mode to use if you are modeling using reference images.
Auto Adjust Distance
When Auto Adjust Distance is turned on, perspective is adjusted in order to avoid clipping of the model and keep it in view. This can exaggerate the perspective distortion as the model is scaled larger.
With the Auto Adjust Distance switch turned off, as well as Local turned off, the camera will pass through the model, allowing the interior to be viewed. Also the same degree of perspective distortion will be maintained whatever the scale of the model.