[b]Locations of Object O and Focal point F are draggable;[/b] so are the handles of the green measuring bars.[br][br]Lens is a converging lens for f > 0, diverging lens for f < 0.[br][br]Light always travels from left to right in this applet, regardless of position of object. Object is virtual if placed to right of lens.

[list][br][*]Shift-Drag on the background to pan the view, or Shift-mousewheel to zoom in & out.[br][*]Shift-Drag on the x or y axis (when visible), to zoom just that axis.[br][*][i]Additional zoom options in the right-click context menu.[/i][br][/list]