I photographed the two images above to demonstrate one very cool bit of knowledge about photography – lens compression. The longer your lens the more compressed, or blurry, your background will be. Both images used the exact same exposure, light, subject, etc – the only difference is that I used a different lens for each shot. A longer lens is going to create the perception that the background is actually closer to your subject, and, in this case with the lights in the background, the more zoomed-in you are to your subject the larger your background bokeh will be.

The image on the left was photographed with a Canon 70-200 f/4L IS lens, zoomed all the way out to 200mm. For the image on the right I used my 24-105 f/4L IS, zoomed all the way to 105mm. (Note that I am using a Canon 7D, which is a crop-sensor camera so the focal length is actually a little bit longer).