I want a portrait prime lens, but someone suggested getting a macro instead, such as the Sigma 105mm f/2.8. Is this good advice?

Chris says… There is a lot of sense in this suggestion as a macro lens can often double as a portrait lens, giving you two useful primes in one.

A portrait lens typically has an effective focal length of around 100mm. That means using a 100mm lens on a fullframe camera, or a 60mm or 70mm one on a DX APS-C camera, like your D300s. This angle of view is great for portraiture as it avoids the facial distortion given by wider lenses, but doesn’t force you to be too far from you subject. A portrait lens also needs a wide maximum aperture to blur backgrounds, but most macro lenses give you a maximum aperture of f/2.8, which is more than adequate.

The Sigma 105mm f/2.8 EX DG HSM is a superb macro lens, and a firm favourite in recent group tests. The focal length is a touch too long for portraits, but fine should you upgrade to full-frame. For a shorter macro, I’d recommend the Nikon 60mm f/2.8D, which I personally use.