画像ホバー半透明css

#main_contents a:hover img{
opacity:0.7;
filter: alpha(opacity=70);        /* ie lt 8 */
-ms-filter: "alpha(opacity=70)";  /* ie 8 */
-moz-opacity:0.7;                 /* FF lt 1.5, Netscape */
-khtml-opacity: 0.7;              /* Safari 1.x */

}