I have a 10-22, 28-135 and want to add the 70-300 DO to make a compact three lens travel kit that covers everything from super wide to telephoto with my 20D. The 28-135 focuses fairly close and with extension tubes can do macro shots, but it is not all that sharp. I may replace it with either the 17-55/2.8 or 24-70/2.8 to get a faster, sharper lens. The 17-55 is EF-S and won't work with my extension tubes, so I would have to use the 70-300 with extension tubes for macro shots. Since the 70-300 uses diffraction optics I do not know how well the image holds up with extension tubes. I imagine it would be OK, but would like to confirm it with someone who has used the combination.