Interested in the Tamron 18-270mm - it states that it's "Equivalent" to a 28-419mm... I have your standard kit Canon 75-300 - will this 270mm lens get closer than my 300mm ?? I think it's referring to a 35mm lens, but what do they mean? - How will a person know that, in this case and others, a 270mm will get closer than a 300mm ???