No extension tubes needed
with a macro-lens.
you can also use them to extend the magnification of the macro-lens.
Unfortunately the IQ will suffer esp. when just using a "normal" lens or a zoom, as you'll leave the parameters that this lens was corrected for.
Use a well corrected close-up lens
to screw in front of your camera-lens (Canon 500D at around 100$).
Or use a tele-converter
(more expensive) that improves magnification by the same factor as the focal length of your lens (max. 2x), so if your lens went down to say 1:3.8 it will go down to 1:1.9 with a 2x tele-converter.
IQ-wise the close-up lens might be the best alternative, as the tele-converter halves the resolution of your lens.
But to answer your question directly: no, I have no experience with extension tubes
Thomas (beware: Nikon-fanboy and moderator!) My Lens Reviews
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