Canon F-1 The professional workhorse of the 1970s for canon.
The first F-1 was released in March of 1971 and was updated in 1976 to the f-1n. There are very few obvious clues as to the differences at first glance. The main one is the F-1n has a film reminder holder.
Wikipedia has a list of all the changes.
"In 1976, the camera was revised slightly. This revised version is sometimes called the F-1n (not to be confused with the 1981 New F-1). All told 13 improvements were made. These changes were:
1.Change the standard focusing screen from the A style (microprism only) to E style (split image with microprism ring).
2.Widen the film advance lever offset from 15 degrees to 30 degrees.
3.Decrease the winding stroke from 180 degrees to 139 degrees.
4.Increase the maximum ASA from 2000 to 3200.
5.Added a plastic tip to the advance lever.
6.Changed the mirror to transmit more blue light, thus making the image brighter.
7.Added a detent to the rewind crank to allow it to stay put when pulled out.
8.Added the capability to take a screw-in type PC sync socket.
9.Spring load the battery check position of the power switch.
10.Increase the size of the shutter release cup.
11.Added a soft rubber ring around the eyepiece.
12.Added a film reminder holder to the camera back.
13.Simplify multiple exposure procedure.
I highlighted the easiest means of seeing which is which.
The NEW F-1 was from 1981 and continued to around 1992 although it was in the catalogue until 1994. This camera looks the same as the F-1n and reall very hard to tell the different, the easiest way for me, is to open the back and see the manufacture date.
I managed to get one of each although my F-1n is needing parts like a prism and a base plate. It works fine and I did manage to find a B type prism.