I have a Nikon D80 with a kit 18-135mm lens. I recently did a course where the instructor said I should upgrade the lens (for landscape photography) to a 10-20mm one for better picture quality. Probably a Sigma.
Do people agree? What benefit will I see in my pictures? Nikon or Sigma?
She also didn't seem keen on Nikon for some reason and said the camera 'to have' was a Canon EOS-5D. Is it worth buying upgraded lenses for mine or saving up for a new camera instead?