The usefulness of an AF motor on a half frame (APS-C, 24x16mm, Nikon calls this "DX") camera is limited anyway.
ALL lenses which need an AF motor in the lens are full frame (small format, 36x24mm, Nikon calls this "FX"). Since the 1.5x crop factor applies, for example a 50mm lens on half format will give the field of view of a 75mm lens on full format.
Additionally, using a full frame lens on a half frame camera means the lens is twice as big, heavy and often much more expensive.
It should be added that using an AF instead of AF-S (the former needs the motor in the camera, the later has a builtin motor) lens on a Nikon will yield various issues:
- Using the external motor isnt silent (thus AF-S for "silent")
- Using the external motor isnt as precise; small movements might result in misfocus
- Using the external motor means the focus ring on lens itself will often move, too
Thus the builtin motor is really not that important, unless you plan to move to full frame soon and thus only want to buy full frame lenses and plan to get some AF lenses (after all theres plenty of good glass to be found there, some of which dont have an AF-S counterpart in the first place).
What ?
AF-S lenses have a built in lens motor.
AF/AF-D lenses require the use of a camera body with a built-in motor (such as d7x00 series or all FX cameras)
"ALL lenses which need an AF motor in the lens are full frame" ==> No, Nikon makes lenses for all their cameras in the AF-S with the AF motor in the lens. FX, DX, the 1 cameras, etc.
"Additionally, using a full frame (FX) lens on a half frame (APS-C / DX) camera means the lens is twice as big, heavy and often much more expensive." ==> Not really. There are lens options out there.
The 50mm AF-D lens is 1/2 the cost, 1/3 the size of the AF-S lens. Both are available new.
Comparing equivalent FX to DX AF-S lenses will be different as the DX lens uses smaller glass elements as it creates a smaller image to the smaller sensor. This is why they are smaller and cost less.
It is true that specialty lenses such as the 24-70/2.8 and 70-200/2.8 are FX designed lenses and there is no equivalent DX lens for comparison.
The only good comparison is the 85mm/1.8G at $480 vs the 85mm f/3.5G DX lens which is $530. But most FX lenses are more expensive as they are designed for a larger sensor.
Here's an visualization of sensor sizes, for Full Frame (FX) and APS-C (DX) cameras and other cameras.
A FX / Full Frame camera such as the d6x0, d7x0, d8x0 etc has a sensor of the 36x24. The DX is a APS-C sized sensor which is are 28x18.6mm ==>
https://lensvid.com/wp-content/uploads/2014/01/Sensors-size-01-01.jpg
I use AF/AF-D lenses all the time.
here's a list of available (as new) lenses from Nikon. They include AF-S, AF-D and also AIS (manual focus) lenses.
==>
DSLR Lenses | Shop All NIKKOR Lenses for DSLR Cameras| Nikon
"- Using the external motor isnt as precise; small movements might result in misfocus" => How did you conclude this?
"- Using the external motor means the focus ring on lens itself will often move, too" ==> I don't understand your point here ? Newer lenses have focus override. But I think on the couple I have the focus ring moves too unless I grab it. On AF/AFD lenses you cannot do focus override unless you turn disengage the focus motor. AF/AF-D lenses dont' have all the modern high tech gadgetry, as they mostly were designed a while ago. Thus they generally cost less than equivalent AF-S lenses.
AF-S lenses are generally larger than AF/AF-D lenses as they have the built in lens motor. Consequently camera bodies without a built-in focus motor are smaller which are the d3x00 and d5x00 series.