I just got my new Canon 20D body and 100mm f2.8 EF USM Canon lens. One thing I was curious about was the focus issue with R lenses, so I took some macro comparison shots with my Leica 100mm F4 Macro Elmar R using a Photodiox adapter on the 20D body. I fully expected, before the tests, no to see any apprecable difference between these lenses. In fact, I guess I expected to the Leica lens underperform in comparison to the faster, more modern Canon lens, which is optimized for the 20D body, yadda yadda yadda. Boy was I surprised. First thing I found out was that the Canon lens gets slower at close focus distances. But the F-stop reading in the finder does not change from f2.8! What a con! This is mentioned in the manual, and I confirmed it by placing a neutral grey card in front of the lens, and adjusting the focus from infinity to the closest focus point, with manual exposure mode on the 20D. If the shutter speed is fixed for a proper exposure at infinity, focusing to close focus drops the exposure by 2 stops. This makes this lens effectively f5.6 at near focus points. The Leica R lens, of course, does no such thing. F4 at infinity, f4 at the close focus endpoint, and R lens is now faster for macro work than the Canon. I tested the focus accuracy (meaning image sharpness) at macro levels of about 1:4 with the Leica lens. With the stock screen in the Canon, I had no trouble focussing, even stopped down 2 or 3 stops. The digital images manually focused (R lens) were as accurate as ones made with the Canon lens auto-focussed. I tried a number of other R lenses from 180mm F2.8 to 24mm, and I had no focus problems whatsoever. I made a couple comparison shots at 1:4 with both macro lenses under flourecsent light, ISO 1600. The Canon lens produced a slightly orange tinted image (large, fine) with no white balance corrections applied (AWB engaged). The Leica R lens, produced white whites with no tint. All body settings were identical for both lenses. Finally, I tried to compare sharpness of both images. I did this by magnifying sections of both images via the viewer LCD on the back of the 20D. I think you can get a 10x magnification this way. Not super critical, but I still found the R lens somewhat sharper. One of the circuit components I was shooting (which is about 0.2" x 0.3") has ID numbers laser etched on one side. Blowing these up to the maximum magnification showed the Leica to be sharper, cleaner, with better contrast. And remember, this is the manually focussed image being compared to the auto-focussed Canon image. These tests clarified a number of things for me. Comments I received in an earlier post about R lenses being impossible to focus on the 20D were incorrect. My faith in R optics is restored, and feedback I have read about superior Canon optics (particularly telephoto lenses) is not the case for the 100 mm Macros.