f is {HEAD ~ the focal length} of the taking lens of {TAIL ~ the photographic film package}, 
f is { HEAD ~ the focal length } of the taking lens of { TAIL ~ the photographic film package } ,
OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD HEAD OTH OTH OTH OTH OTH TAIL TAIL TAIL TAIL TAIL TAIL TAIL TAIL OTH