A professional lens is faster to focus and more durable and weather tight. Also better in low light situations and will not hunt as much. I also think one will out live a kit lens I upgraded my 510 to a higher quality lens and it is the same weight as the camera. Though mine was far from $3000.00 I asure you there is a difference, not so much in picture quality but performance. I get a lot more Keepers with focus and miss less shots. It's kind of like cars. A sedan will get you there but the performance is with the sports car.