Adding extension tubes forces the lens "out of spec", unless the lens is designed specifically to be used with bellows or extension tubes.
I tried the 12mm / 25mm ET on a 70-200 2.8L (IF design), and the focus ring became basically unusable. Significant focus change would occur when changing the FL (zoom) setting. Not only became the lens difficult to use, but also optically it didn't perform well. With a close-up lens the optical characteristics of the internal focusing design are preserved. A single-lens closeup lens will degrade image quality more than a two-element design (such as the 500D). Of course more lens surfaces also means more chance for flare. Lars -- .~. Lars Michael /V\ [EMAIL PROTECTED] /(_)\ http://www.larsmichael.com/ ^^ ^^ * **** ******* *********************************************************** * For list instructions, including unsubscribe, see: * http://www.a1.nl/phomepag/markerink/eos_list.htm ***********************************************************
