window.addEvent('domready', function() {
    
    var thumb = $$('.thumbnails');
	    
    thumb.each(function(el){
    
	    thumb.setStyle('opacity', 0.5);
	    el.addEvent('mouseenter',function(){
	    	el.set('tween', {duration: 100});
			el.tween('opacity', 1);    
	    });
	    el.addEvent('mouseleave',function(){
	    	el.set('tween', {duration: 500});
			el.tween('opacity', 0.5);    
	    });
	    
	 });

});