I am not a photographer but my wife is and I like to get her lens. She has been renting a nikon 24-70 for wedding shots and I want to get her one. I am so confused with Tamron or Nikon. But I am not sure what the difference between the 24-70 and 24-85 is besides price. Could someone help me understand the difference. I know I can get a used Tamron for $1000 and $1700. Any help would be greatly appreciated.