Sun 26-Aug-12 01:16 AM | edited Sun 26-Aug-12 01:49 AM by Leonard62
Prior to 1977 all Nikon lenses were non-AI. That means the only way these lenses could access the cameras meter was the prong on the back of these lenses would contact a lever up in the viewfinder area of the body. The bottom of these non-AI lenses had the black tube around the chrome mount was perfectly flat and over-lapped the mount.
When nikon developed the AI mount they put the meter coupling lever at the 1 o'clock position above the camera mount. In order to contact this lever the bottom of the lens where it overlapped the chrome mount had a couple cutouts which would contact and position the AI lever on the body.
If the bottom of the lens is perfectly flat with no cutouts that portion of the lens barrel will contact the AI lever and possibly break it. The bottom of the barrel will also contact and possibly break another little lever that is located at the 7 o'clock position around the body lens mount.
So it's not a case of it just not fitting but it will possibly create an expensive body repair.
edit: Your D90 does not have the 1 o'clock position lever on the body but it does have the 7 o'clock lever. Your D7000 has the 1 o'clock lever and the 7 o'clock lever.
If your lenses are non-AI they can be converted to AI by machining away some of the lens barrel around the chrome lens mount. However the cutout must be positioned precisely so when it moves the AI lever on the body the meter knows what f stop the lens is set to.
Nikon's AF-D lenses with aperture rings have AI mounts with the cutouts. The G lenses without an aperture ring don't have the AI cutout mount since the lens aperture info is sent to the meter electronically rather than mechanically. The lens barrel of the G lenses is constructed with clearance so it doesn't interfere with the body AI lever or the 7 o'clock lever/button.