Mike some of the best closeup filters or (diopters) are now made by Canon , for small focal length lens a Canon 250 D works best , they come in several different sizes 52mm and 58mm for lens of 100mm or over you have the 500D.

Diopters don't degrade image quality if you buy the best diopters . There is also no loss of light, like when using Extension tubes.

Tom Hicks , http://www.fredmiranda.com/forum/board/45

http://www.shutterfreaks.com/Tips/tomhicksmacros.html
http://www.shutterfreaks.com/Tips/Tips.html

Hope this helps.