css opacity

IE 總是不接受css 的standard
明明css2 已有opacity....

.opacity50{

  -ms-filter: "progid:DXImageTransform.Microsoft.Alpha(Opacity=50)";  /*IE8 or bove*/

  filter: alpha(opacity=50); /*IE 5.5 or above*/

  opacity:0.5; /*other browser*/

}