一段图片放大的代码，大家改下！

下面能实现一个放大境的效果，可是放大的倍数太大了，请高手指点下，改哪里，才能缩小放大的倍数？谢谢了！
<script language="javascript">var zoomw=250;
var zoomh=220;
var defzoomamount=4;
var zoomamountstep=1.2;
var zoomsizemin=1000;
var zoomsizemax=100000;
var zoomsizestep=1.2;
var zoomamountmin=1;
var zoomamountmax=12;
function zoom_set(evt) {
var evt = evt?evt:window.event?window.event:null; if(!evt){ return;}
if(zoomid=='' || parseInt(document.getElementById(zoomid+'_container').style.width) == 0) {return true;}
if(evt.keyCode==37 || evt.keyCode==100) {zoomw/=zoomsizestep; zoomh/=zoomsizestep; if(zoomw*zoomh<zoomsizemin) {zoomh=Math.sqrt(zoomsizemin/zoomratio); zoomw=zoomh*zoomratio;} zoom_init(); zoom_move(); return;} //left
if(evt.keyCode==39 || evt.keyCode==102) {
zoomw*=zoomsizestep; zoomh*=zoomsizestep;
if(zoomw*zoomh>zoomsizemax) {zoomh=Math.sqrt(zoomsizemax/zoomratio); zoomw=zoomh*zoomratio;}
if(zoomw>objw) {zoomw=objw; zoomh=objw/zoomratio;}
else if(zoomh>objh) {zoomh=objh; zoomw=objh*zoomratio}
zoom_init(); zoom_move(); return;
} //right
if(evt.keyCode==40 || evt.keyCode==98) {zoomamount/=zoomamountstep; if(zoomamount<zoomamountmin) {zoomamount=zoomamountmin;} zoom_init(); zoom_move(); return;} //down
if(evt.keyCode==38 || evt.keyCode==104) {zoomamount*=zoomamountstep; if(zoomamount>zoomamountmax) {zoomamount=zoomamountmax;} zoom_init(); zoom_move(); return;} //up
return;
}
function zoom_init() {
document.getElementById(zoomid+'_clip').style.width=objw*zoomamount+'px';
document.getElementById(zoomid+'_clip').style.height=objh*zoomamount+'px';
setTimeout("document.getElementById('"+zoomid+"_trigger').focus();",0);
}
function zoom_move(evt) {
if(typeof(evt) == 'object') {
var evt = evt?evt:window.event?window.event:null; if(!evt){ return;}
if(evt.pageX) {
xx=evt.pageX - ffox;
yy=evt.pageY - ffoy;
} else {
if(typeof(document.getElementById(zoomid)+1) == 'number') {return true;} //mert az ie egy ocska kurva
xx=evt.x - ieox;
yy=evt.y - ieoy;
}
} else {
xx=lastxx; yy=lastyy;
}
lastxx=xx; lastyy=yy;
document.getElementById(zoomid+'_clip').style.margin=((yy-zoomh/2 > 0)?(zoomh/2-yy*zoomamount):(yy*(1-zoomamount)))+'px 0px 0px '+((xx-zoomw/2 > 0)?(zoomw/2-xx*zoomamount):(xx*(1-zoomamount)))+'px';
document.getElementById(zoomid+'_container').style.margin=((yy-zoomh/2 > 0)?(yy-zoomh/2):(0))+'px 0px 0px '+((xx-zoomw/2 > 0)?(xx-zoomw/2):(0))+'px';
w2=((xx+zoomw/2<objw)?((zoomw/2<xx)?(zoomw):(zoomw/2+xx)):(zoomw/2+objw-xx)); if(w2<0) {w2=0;} document.getElementById(zoomid+'_container').style.width=w2+'px';
h2=((yy+zoomh/2<objh)?((zoomh/2<yy)?(zoomh):(zoomh/2+yy)):(zoomh/2+objh-yy)); if(h2<0) {h2=0;} document.getElementById(zoomid+'_container').style.height=h2+'px';
return false;
}
function zoom_off() {
document.getElementById(zoomid+'_container').style.width='0px';
document.getElementById(zoomid+'_container').style.height='0px';
zoomid='';
}
function countoffset() {
ieox=0;ieoy=0;
for(zmi=0;zmi<50;zmi++) {
zme='document.getElementById(zoomid)';
for(zmj=1;zmj<=zmi;zmj++) {
zme+='.offsetParent';
}
if(eval(zme)+1 == 1) {zmi=100} else {ieox+=eval(zme+'.offsetLeft'); ieoy+=eval(zme+'.offsetTop');}
}
ffox=ieox;
ffoy=ieoy;
ieox-=document.body.scrollLeft;
ieoy-=document.body.scrollTop;
}
function zoom_on(evt,ow,oh,lowres,highres) {
thisid=lowres+highres+ow+oh;
thisid='zoom_'+thisid.replace(/[^a-z0-9]/ig,'')
if(zoomid==thisid) {return;}
if(typeof(highres) == typeof(nemistudom)) {highres=lowres;}
var evt = evt?evt:window.event?window.event:null; if(!evt){ return;}
zoomamount=defzoomamount;
objw=ow;
objh=oh;
zoomid=thisid;
if(evt.pageX) {
evt.target.parentNode.id=thisid;
countoffset();
lastxx=evt.pageX - ffox; //mert a ff egy ocska kurva
lastyy=evt.pageY - ffoy;
} else {
evt.srcElement.parentNode.id=thisid;
countoffset();
lastxx=evt.x - ieox; //mert az ie egy ocska kurva
lastyy=evt.y - ieoy;
}
document.getElementById(thisid).style.width=ow+'px';
document.getElementById(thisid).style.height=oh+'px';
document.getElementById(thisid).style.overflow='hidden';
document.getElementById(thisid).innerHTML='<div style="position:absolute; overflow:hidden; width:0; height:0;" id="'+thisid+'_container" onmousemove="zoom_move(event);" onmouseout="zoom_off()"><img src="'+highres+'" alt="" id="'+thisid+'_clip" style="padding:0;margin:0;border:0;" /></div><img src="'+lowres+'" id="'+thisid+'_pic" alt="" style="padding:0;margin:0;border:0;width:'+ow+'px; height: '+oh+'px"/><input type="text" id="'+thisid+'_trigger" style="width:0;height:0;border:0;margin:0; padding:0;overflow:hidden;"/>';
if(zoomw>objw) {zoomw=objw; zoomh=objw/zoomratio;}
else if(zoomh>objh) {zoomh=objh; zoomw=objh*zoomratio}
zoom_init();
zoom_move('');
if(document.all) {
document.onkeydown=zoom_set;
} else {
window.captureEvents(Event.KEYDOWN);
window.onkeydown = zoom_set;
}
return false;
}
var zoomamount=defzoomamount; var objw;var objh;var zoomid=''; var zoomratio=zoomw/zoomh; var ieox=0; var ieoy=0; var ffox=0; var ffoy=0;
</script><div style="float:left" onmouseover="zoom_on(event,200,175,'image312/DSC03123.JPG','image312/DSC03123.JPG');" onmousemove="zoom_move(event);" 
onmouseout="zoom_off();"><img src="image312/DSC03123.JPG" width="200" height="175"/></div>
<div style="clear:both;"></div>