film SLR lenses, the AF Nikkor G type (2000) lacking an aperture control ring; and the AF Nikkor DX type (2003) with image circles sized for Nikon's digital SLRs will mount, but will not function properly at all. The FT also had two PC terminals to synchronize with flash units: an M-sync to all speeds for M and FP type (1/60 second for MF type) flashbulbs and an X-sync to 1/125th second for electronic flashes using guide number manual exposure control. However, the FT did not have a built-in accessory shoe to mount flash units. The "Nikkormat accessory shoe" must be screwed to the top of the pentaprism cover via the eyepiece first. Note that this shoe only mounts the flash. A PC cord must still be plugged into the appropriate PC terminal. This was normal for most SLRs of the 1960s. Nikkormat FS The Nikkormat FS, manufactured from 1965 to 1971, was an FT stripped of the built-in light meter with its exposure information system and the mirror lockup feature. The FS was unpopular when new because of the lack of a built-in meter, but this makes it rarer and more valuable than the FTs to collectors today. Nikkormat FTN The Nikkormat FTN was manufactured from 1967 to 1975. It simplified the lens mounting procedure of the rabbit ear Nikkor lenses. The meter coupling pin on the camera still had to be aligned with the meter coupling shoe on the lens, but the lens maximum aperture no longer had to be manually preset on the FTN. Instead, the lens aperture ring had to be turned back and forth to the smallest aperture (largest f-stop number) and then to the largest (smallest number) immediately after mounting to ensure that the lens and the FTN couple properly (Nippon Kogaku called it indexing the maximum aperture of the lens) and meter correctly. This system seems unwieldy to today's photographers, but it was more efficient and easier than before, and became second nature to Nikon and Nikkormat photographers of the 1960s and 1970s. In addition, the FTN improved the metering system to the now classic Nikon 60/40 percent centerweighted style. The viewfinder also added +/– over/underexposure metering markers and set shutter speed information. The FTN also offered a choice (made at purchase time or by replacement at factory service centers) of brighter fixed viewfinder focusing screens: Nippon Kogaku's standard Type J with central