<div id="msgcns!45806B8A57D785F7!838" class="bvMsg"> <br /> <br /> <a href="http://phet.colorado.edu/simulations/sims.php?sim=Geometric_Optics">Geometric Optics </a> <br /><br /> How does a lens form an image? See how light rays are refracted by a lens. Watch how the image changes when you adjust the focal length of the lens, move the object, move the lens, or move the screen <br /></div>