I have owned both F1n & New F1, ( or as I like to call it New F1N, that covers all the bases ). You will notice with Canon's Mark II, nonsense, it still can't name a camera worth a damn.
O.K. If you have a camera with an AE prism, you have a New F1. The New F1, with AE prism comes standard with an A screen. With the normal prism it's a P Screen. This was explained above,so I won't duplicate it here.
The AE prism, when the shutter is locked on " A ", gives you Aperture Priority, controlled from the
Aperture Dial.
With the addition of a winder or Motor, you can have Shutter Priority, by locking the aperture dial on " A " & controlling the exposure by the Shutter Speed dial.
If you put both of the camera's shutter & aperture dials on " A ". You get an Unknown Error. It won't tell you, but they never designed it to work that way & everything will be under exposed. It
should have given yo a Program Mode, but it's a Pro camera, which didn't have such things.
Get the Motor Drive FN. It gives you a faster advance speed, plus the added benefit of Motorized rewind. It's really a joy, to watch the rewind knob spin around unassisted.
The Original F1 Motors never had this feature.
My biggest problem was that I was having the Shutter Priority underexposure everything. It took a total of 9 months to figure this out including Canon in Irvine, CA., U.S.A.. They would take the Motor off & test the camera, which would test fine. Only very methodical testing by me, made the problem apparent.
One final Caveat. NEVER get an Olympic Canon New F1. These can be determined by the gold instead of white lettering. These were among the 1st New F1's. I traded a regular New F1 for it & the Gold one ate batteries something fierce. I know of a friend that had the same problem & it soured him on Canon.
The thing is this problem can be corrected on a White One, if it happens it's rare, once fixed no problem. but it could never be corrected on the Gold one.
Unless, of course everyone was lying to me & never bothered to look at it. But I had already paid for the repair twice, an independent & Canon Irvine, CA., U.S.A..
I finally dumped them all for Canon EOS film bodies which I shoot to this day.
I won't bore you with which.