I've had a Canon 500 D close up lens for a year or two (one of these trinkits you buy but don't really need) . This morning I read in CiC's tutorial on extension tubes/close up lenses that with a close up lens mounted the original lens does not lose its ability to focus on distant objects. Have I misunderstood this? I fitted my close-up to my 70-300 mm zoom and for the life of me can't focus on anything further away than a couple of feet. Can anyone explain this.