var _t1 = 0; //打开页面时等待图片载入的时间
var _t2 = 5; //图片轮转的间隔时间
var _tn = 1;//当前焦点
var _tl =null;
var _ttl = null;

function change_img(){
  setFocus(_tn);
  _tt1 = setTimeout('change_img()',_t2*1000);
}
function setFocus(i){
  if(i>_tnum){
    _tn=1;i=1;
  }
  var focusPicT = document.getElementById('focusPic'+_tl);
  if (_tl && focusPicT){
  	focusPicT.style.display='none'
  }
  
  var focusPicI = document.getElementById('focusPic'+i);
  if (focusPicI){
    focusPicI.style.display='block';
  }
  _tl=i;
  _tn++;
}