Hello, I recently bought the Sigma 18-250mm lens to replace my Nikkor 18-55 and 55-200 lenses. When I took a shot with the 55-200mm @200mm and a shot with the 18-250mm @250mm the 200mm was a closer shot than the 250mm!?!? Can anyone tell me why??? I was really excited to get some extra reach with this lens... but i get less Also, does this mean that if I get an 18-200mm lens it will be way less zoomed in than the 55-200? thanks!