Manufacturer description: Canon Close-Up Lens 500D is a double-element accessory that attaches to front of lens. It changes closest focusing distance from infinity to 500mm (approx. 19.7" from front of lens).
Of all the others we've used over the years, this close-up lens set from UK-based SRB Photographic are what we recommend here at EOS HQ if you can't obtain (or stretch to) the Canon 250D or 500D close-up lenses.
The 500D is a small double-element lens that threads onto the filter threads on a standard (non-macro) lens. It allows that lens to be focused at a much closer distance- resulting in a higher magnification of the subject.