How much additional background blur can I really achieve at f/1.8 vs f/2.8 at 85mm? I'm considering adding a Nikon 85mm f/1.8G to my kit. This is all about portraits. I already have a Tamron 90mm f/2.8 Macro 1:1, which is a decent portrait lens. Though the Tamron is usable at f/2.8, I'm not completely happy with its sharpness until I stop down to f4 or beyond. This is mostly for an FX camera, a D600. Though it may see action on a D7100 as well. Would I be wasting my money?