Every lens before the AF-D also had diaphragms, so why no letter D on those ? QED
D means distance information. It let the camera know at what distance the camera is focused.
Copied form KRs Website directlty:
" "D" means these lenses let the camera know the distance at which the lens is focused. All lenses introduced since 1992 have been "D."
This can help the camera set flash exposure more accurately if the subject occupies only a small part of the frame, or if you're shooting into mirrors or very light or dark subjects. With non-D lenses the camera is more likely to get tricked into the wrong exposure in these odd cases.
On digital SLRs introduced since about 2010, they can often correct lens distortion, but only with D lenses.
If you are buying used lenses on a budget you can get the earlier non-D versions cheaper, and if you are considering updating a non-D lens to D, don't bother unless you shoot a lot of
fill-flash.
In fact, the instruction manual of the 105mm f/2.8D AF Micro-Nikkor cautions that the D feature of the lens can lead to the WRONG EXPOSURE unless you keep your flashes at the same distance from the subject as the film, which is a real obstacle to creativity.
There are a couple of ways to signify a "D" lens: Nikon usually marks its lenses as "50mm f/1.4D AF" as opposed to "50mm f/1.4 AF-D," but it all means the same thing.
Most AF-D lenses are AF and AI-s, and work great on manual focus cameras. You'll need to have a coupling prong added for use with the meter on ancient pre-AI cameras.
The D feature has no direct relation to autofocus speed, however as Nikon introduced newer D versions of existing lenses they sometimes sped up the autofocus speed, too. The Nikon
70-210mm f/4-5.6 is an example of this; the D version focuses several times faster than the earlier one. The speed comes from a change in mechanical gearing inside the lens; not the D feature itself.
Focusing speed has nothing to do with whether or not a lens is D. Of course newer lenses are D and newer lenses tend to focus more quickly, but the focus speed is determined by the gearing between the AF coupler and the focus ring, not the D feature alone.
All the newest AF lenses, especially every
AF-S,
AF-I and especially
G, are also D. Nikon doesn't bother to mark it anymore on the newest models."
Nikkor Lens Technology
When it comes to lenses, i don't think there is anyone else as thorough