IE7 滤镜无法正常显示

[zkyarcher]

IE7
IE8
请问大神们 ie7的半透明渲染是不是和IE8的半透明渲染不一样
html代码

   <div class="yzsj">
     	   <div class="activity_goods" style="z-index: 1"><a href="${ctx}/searchshopInfo/3206011016.html" target="_blank"><img src="http://*******/indexpic/nf_activitygoodspic_129.jpg"></img></a><div class=""></div></div>
           <div class="activity_goods" style="z-index: 3;left: 265px;"><a href="${ctx}/searchshopInfo/3206011069.html" target="_blank"><img src="http://*******/indexpic/nf_activitygoodspic_130.jpg"></img></a><div class="zhe"></div></div>
           <div class="activity_goods" style="z-index: 5;left: 425px;"><a href="${ctx}/searchshopInfo/3206011102.html" target="_blank"><img src="http://*******/indexpic/nf_activitygoodspic_131.jpg"></img></a><div class="zhe"></div></div>
           <div class="activity_goods" style="z-index: 7;left: 585px;"><a href="${ctx}/prize/prizeIndex" target="_blank"><img src="http://*******/indexpic/nf_activitygoodspic_128.jpg"></img></a><div class="zhe"></div></div>
     
      </div>
    </div>

css 代码

.activity_goods{float: left;position: absolute;z-index:1}
.activity_goods .zhe{
	filter: alpha(opacity=50);
	-moz-opacity: 0.5;
	opacity: 0.5;
	z-index: 100;
	background-color:red;
	float: left;
	width: 100%;
	height: 100%;
	position: relative;
	z-index: 2;
	top:0px;
}

求大神帮忙 ie7为什么不能正常显示滤镜效果