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