Camera Labs

Two things define a lens for portraiture in my book:
- a focal length that matches your requirements
- a larger aperture, at least f/2.8, better f/2.0 or f/1.8.
The latter is the reason why your existing lenses will ultimately disappoint you in shooting portraits although they certainly cover any conceivable range of working distances: They have only small apertures.
So the AF-S VR 105/2.8 certainly could do a very good job with regard to macro photography and quite a decent job re portraiture.
But if the working distance of the 105mm for portraits is too long for you there is a cheap(er) alternative: The Nikon AF-S Micro 60mm 2.8G ED! The only thing that you give up when you get this lens is the image-stabilization of the 105mm macro. Image quality should be very good - see a review here, where it gets a 4 star rating!

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Thomas (beware: Nikon-fanboy and moderator!) My Lens Reviews, My Pictures, My Photography Blog
D800+assorted lenses