Telephoto lenses have an additional benefit of allowing you to crop out most of the background. The longer the focal length, the stronger this effect. Telephoto lenses will also provide a shallower depth of field, gently blurring the background to help reduce distractions from your subject.
Speaking of depth of field, prime lenses and zooms with a constant aperture of ƒ/2.8 or faster are preferable for portrait work due to their ability to further reduce depth of field when shooting wide open.
Canon’s EF 70-200mm ƒ/2.8L IS II USM can be used with both full-frame- and APS-C-sensor Canon cameras (equivalent to 112-320mm with APS-sensor models), with a constant ƒ/2.8 maximum aperture throughout the zoom range. List Price: $2,199.
Fujifilm’s new Fujinon XF50-140mm ƒ/2.8 R LM OIS WR zoom provides a constant ƒ/2.8 aperture across the 35mm-equivalent focal range of 76-213mm when paired with Fujifilm X-series cameras like the new entry-level X-A2. List Price: $1,599.
The AF Zoom-Nikkor 80-200mm ƒ/2.8D ED can be used with both FX- and DX-format Nikons, the latter providing a 35mm-equivalent focal range of 120-300mm. It also maintains a fast ƒ/2.8 aperture throughout the range. List Price: $1,224.
For Olympus PEN and OM-D cameras, the M.Zuiko ED 40-150mm ƒ/2.8 PRO delivers a 35mm-equivalent focal range of 80-300mm with a constant ƒ/2.8 maximum aperture. List Price: $1,499.
Panasonic’s LUMIX G X VARIO 35-100mm F/2.8 ASPH also features a constant ƒ/2.8 maximum aperture across its 70-200mm (35mm-equivalent) focal range. List Price: $1,499.