If I only had one portrait lens for my Nikon, it would be the Nikkor 70-200. No questions. But the Tamron 70-200 is a lot less expensive and 95% as good. Next, I'd want a 24-70mm f/2.8, and for that one I'd actually PREFER the Tamron since it has image stabilization. Last, I want a super fast prime like the Sigma 85mm f/1.4. The Nikkor 85mm f/1.4 is probably a tiny bit better, but the Sigma is really really close for a lot less money. With those three lenses I would feel 100% confident shooting any portrait photography job.
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