The FM, FE, and F3 will let you flip the AI follower out of the way so you can use non AI lenses in stop down metering with no damage to the camera. Your FTN will use any lens that has the rabbit ears and if you look at AIS and some of the early auto focus lenses you'll see two little dimple around the f5.6 mark where the ears can be mounted. Biggest problem wiyh your camera is that it uses the discontinued Mercury 1.3 volt battery, but there are work arounds, a hearing aid battery placed inside a #10 "O" ring will work but life is short. Thers an adapter I believe called a L-9 that will allow you to use the 1.5 LR and SR batteries. If you move up to the Nikkormat FT2 you can use the 1.5 battery and stll use your Non AI lens. By the way, you can tell the differenc in AI and Non AI by the rabbit ears Non AI are solid AI have holes in them, If no rabbit ears, probably AIS or Series E. I still have my FTN, mostly from nostalgia, in 68 in Natrang, RVN, as I was climbing out of a truck a rocket exploded , 3 pieces shrapnel in my torso, 2 hit the back of the camera and the rest went into the door. Without the camera hanging around my neck all 5 would have been in me!