I had a feeling about posting other people's photos, that's why I stated that it wasn't mine, just in case. I know for next time!
I just wanted a few opinions, that's all. I knew aperture played a part in capturing this shot. I really like the lighting in the background, almost like a haze, and I'm just curious as to which settings or techniques could have been used to get this.
You will struggle to get that kind of seperation with either zoom, but maybe wide open with your 50mm. Get in position to fill the frame with your subject and try and have the background as far away as possible to render it oof completely, try at f1.8, which wont be the sharpest setting on this lens, but this type of photo it may work. Take a few shots and try keep the eyes in focus, tiny, tiny movements will put them oof, which you don't want.
Also make sure that the shutter speed is fairly high, @ f1.8 it should be, but keep it at least 1/125 but more if possible, use iso to keep the ss up. Do this all in aperture priority. Try f2.2 and 2.8 also, these should be sharper but its a balance between being really oof background and subject sharpness