70-300 DO IS + extension tubes

I am considering getting the 70-300 DO as a compact travel lens, but note that it does not focus very close. Sometimes I want to take macro shots. I am concerned that the diffusion type optics might not take kindly to the use of an extension tube.

Has anyone used this lens with extension tubes? I would appreciate your comments.

i really doubt that lens would be too great with tubes. what other lenses do you have? my 50 works great with my tubes.

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.

Tubes don't introduce anything into the light path, so they shouldn't (except at extremely long extensions) have much effect on the lens. They're not like teleconverters, just a bunch of air between the back of the lens and the body.