[abenedik]

When you use ZoomPanelNavigator it by default limits the zoom factor to the limits defined by the ZoomPanelNavigator.MinZoomFactor and ZoomPanelNavigator.MaxZoomFactor properties. But you can disable this by setting the ZoomPanelNavigator.IsZoomPanelLimitedToMinMaxZoomFactors to false. You can also change the limits so they will suit your needs.

See ZoomPanelNavigator sample that comes with ZoomPanel samples project for more info.