IE兼容opacity

filter:alpha(opacity=80); 

opacity: 0.57;                 /* Firefox, Safari(WebKit), Opera) 
filter: "alpha(opacity=57)";   /* IE 8 */
filter: alpha(opacity=57);     /* IE 4-7 */
zoom: 1; 

-ms-filter:"progid:DXImageTransform.Microsoft.Alpha(Opacity=50)";  
filter:progid:DXImageTransform.Microsoft.Alpha(Opacity=50);