About rabbit ears mounting onto Fm2?
Sorry for the noob question, i have read info on the old nikkor lens and found out that my current ai-s lens do not have the R.ear or it could be missing i don't know.
Most importantly i want to know is, does my Fm2 needs it? Or its only for F2?
Your FM2 doesn't need them, it was only required by the F, F2 and Nikkormats.
It was just easier for third parties to continue to include it (it's also a useful way of identifying a Nikon-fit lens), many FM-2s were sold with the budget 50mm f1.8 series E, which had no fork.
Many people hear that the Nikon F mount has remained the same since 1959 and assume there are no compatibility issues like Leica or Pentax but Nikon's method for indexing the lenses aperture underwent some major changes from the 1950's through the 1970's.
An AIS lens should have come from the factory with the "rabbit ears", "crab claw" or "fork". AI stands for "Automatic Indexing". What this means is that when you mount an AI, AIS E Series or newer lens, you don't have to do "the Nikon Shuffle" in order for the camera to "know" the lens's maximum aperture.
The camera's meter needs to "know" the aperture range of every lens mounted in order to correctly set exposures. On Pre-AI, sometimes called Non-AI lenses, that Indexing Fork on the lens connects to linkage on the camera body and this connection communicates changes in the lens aperture to the light meter. AI and AIS lenses still featured this Indexing Fork so that the lenses would be backwards compatible with, as Andrew mentions, the Nikon F, earlier F2's and earlier Nikkormat models.
Your FM2 was build well after Auto Indexing became common on Nikon's bodies and lenses so there's no need to worry about this Indexing Fork on an AIS lens. However, you Can't mount a Pre-AI lens to the FM2 unless the lens is converted to AI (which can be done for about $30).
Your F2, unless it's an F2a, F2as or non-photomic (no light meter), requires use of lenses with the Indexing Fork in order to communicate that lens aperture to the camera's light meter. Clearly if your F2 is an early model with no meter, you don't need the fork.
If you are using an F2 that DOES have a meter (photomic) and is not an F2a or F2as, you MUST do the "the Nikon Shuffle" when mounting a lens to the camera. On the F2, you mount the lens as normal but then you must SHUFFLE the aperture ring on the lens from one extreme to the other. You'll notice that once you do this, there's a window on the front of the F2 finder that displays the maximum aperture of your lens in it. If you always use the same lens, you might not have needed to do the shuffle and the maximum aperture was already set. But if you mounted a lens with a different aperture range, failure to do the shuffle would cause your light meter to give incorrect exposure information. On Nikkormat models, you must first set the lens for f5.6 before mounting the lens, and then do the shuffle once the lens is mounted. The FM2 allows you to simply mount the lens and go, no shuffle. The aperture indexing is done by linkage inside the lens mount of both the lens and the body so it looks more streamlined and no shuffle is required.
I'm also a Nikon shooter and use both non-auto indexing bodies and auto indexing bodies and therefore, the best buy for me are AI and AIS lenses since they can be used on both types of bodies.
Say what you will about Ken Rockwell but this page he wrote up about Nikon lens compatibility is the bible for a classic Nikon photographer. Read this and you'll learn all you need to know about these mounts:
http://www.kenrockwell.com/...y-lens.htm
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