TS is having a 18-135mm f3.5-5.6 IS USM lens,
at 18mm focal length setting (equivalent to 24mm on FX), is good for environmental portrait
at 24mm focal length setting (equivalent to 35mm on FX), is good for full length shot
at 35mm focal length setting (equivalent to 50mm on FX), is good for three quarter shot
at 50mm focal length setting (equivalent to 50mm on FX), is good for half length shot
at 85mm focal length setting (equivalent to 125mm on FX), is good for head and shoulder shot
at 105mm focal length setting (equivalent to 150mm on FX), is good for close up head shot
this lens is already cover whatever constitute the ideal focal length to create a good portrait,
portraits is not able about giving shallow depth of field, or bokeh, if this is what most people think, than their definition of good portrait is as shallow as the depth of field they are looking for.