"Canon 72mm 500D Close-up Lens - Close-up lenses are for quick and easy close-up photography. The close-up lens is screwed on to the front of a lens like a filter. Close-up lenses 250D and 500D have two achromatic elements to correct chromatic aberrations. They do not degrade the high optical performance of EF lenses.
The 250D is suited for lenses with a focal length anywhere from 30 to 135mm. The 500D is geared for lenses with a focal length anywhere from 70 to 300mm."