Maybe this is a silly question...

[Skoropada]

I've been reading about lenses recently and in many reviews I found many comments about the focusing speed.

My doubt is if the focusing speed is inherent to the lens or if it is more related to the camera.
Is the focusing speed related to the mechanics or to the optics of the lens/camera?

I know that some lenses have their own motors, but some others are moved by the camera, so mechanics surely play a part in here.

Can someone shed a light over this issue?

[IABoomer]

I would say if the lens has a built-in motor, then that will take precedence over a camera-body motor, so everything about the focus speed will be lens-related, not body-related.

I found this discussion on Flickr specifically discussing using AF-S (servo lenses) on a D90, and how the D90 doesn't use the camera motor to focus the AF-S lenses.

Flickr: Discussing AF-S Build in motor lenses for D90?? in Nikon DSLR Users

[BigVinnie]

Some of both.

With the canon line some bodies are faster at focusing than others. Lenses also have a focus speed based on the motor configuration. Canon has multiple types of focus motors depending on the grade of lens.

3rd party lenses also have different grades of motors in the lenses.