What to look for...
FOCAL LENGTH AND APERTURE ARE KEY CONSIDERATIONS, BUT they ’re NOT THE ONLY FACTORS
A larger number of diaphragm blades tends to produce a more rounded aperture when stopping down. This helps to enhance the quality of the lens’s bokeh.
It’s very rare to find optical stabilisation in a fast lens with an aperture rating wider than f/2.8. The two Tamron VC lenses are the only options on test to feature this.
All of the lenses on test have ring-type ultrasonic autofocus, which works with all Nikon D-SLRs. It’s whisper-quiet and enables full-time manual override.
SEALED MOUNTING PLATE
All of the lenses in the group feature a weather-sealed mounting plate, apart from the Sigma 50mm lens. Assuming you don’t shoot portraits in the rain, this might be a moot point
50mm and 85mm lenses are ideal for DX and FX portraiture, respectively. 50mm lenses work well for wider environmental portraits on FX-format cameras too
An f/1.4 aperture is two-thirds of a stop faster than f/1.8. This enables a slightly tighter depth of field, but in reality it can be hard to tell the difference