I got curious about the back on your s3
on Richard de stoutz nikon f site
he has all the backs shown for nikon f
goggle - nikon f camera backs - Richard de stoutz
the made in Japan with double film indicators & asa to 1600
was on nikon f starting about 67xxx to 68xxx
so after rangefinder cameras & probably a replacement from nikon
nikon f backs are longer & will not fit rangefinder body's
the new backs on the s3 2000 only have one film indicator are marked made in Japan
iso to 400 not asa to 1600 as on 60's cameras