What do you think about the zoom lens Sigma 28-105/2,8-4,0 AF Aspherical? I own a Nikon FE with a excellent nikkor 28mm f2,8 lens but I feel limited in my possibilities since I want to begin to make portraits and travel photography. I need a versatile and bright lens but I don't need the AF. Any suggestion? (I can't afford too much money, my top is about 200 $) Thanks.