Как вывести pop up окно в центре?

<script type="text/javascript">//<![CDATA[ document.write('<a href="javascript:void window.open(\'<?php echo $product_full_image ?>\', \'win2\', \'status=no,toolbar=no,scrollbars=yes,titlebar=no,menubar=no,resizable=yes,width=<?php echo $full_image_width ?>,height=<?php echo $full_image_height ?>,directories=no,location=no\');">');
document.write( '<?php echo ps_product::image_tag( urldecode($product_thumb_image), 'class="browseProductImage" border="0" title="'.$product_name.'" alt="'.$product_name .'"' ) ?></a>' );
//]]>
</script>