{TAIL ~ The imaging lens system} 21, wherein {HEAD ~ the fourth lens element} has a concave object side surface 
{ TAIL ~ The imaging lens system } 21 , wherein { HEAD ~ the fourth lens element } has a concave object side surface
TAIL TAIL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD HEAD HEAD OTH OTH OTH OTH OTH OTH