[wim]

Ah, Wim, you were responding about the 100-400 Mk I. The names I have heard to describe the two different zoom systems are "one touch" for the combined ring as in the Mark I, and "two touch" for the two ring style that is as far as I know virtually all modern lenses now use. I still own at least three lenses that are of "one touch" design. They are all manual focus lenses, though.

 
I like shooting birds in flight (BIFs).
 
Usually I start with AI Servo focus, lens at 100mm, and if I can keep the focus point anywhere near the bird as I zoom ring, the lens stays in focus. The big problem: Getting from 100mm to 400mm and staying on the bird is no mean feat!
 
You've given me a big clue though! I have been keeping the zoom ring tension at maximum to prevent zoom creep. It never occurred to me to set the ring tension to minimum while I was shooting BIF, and then tighten it back up for travel.
 
You've done it again, Wim. I believe this will be a big improvement! Thank you!
 
-Mac

It's only a pleasure, Mac!

BTW, the 100-400 Mk I is also better at close focus, i.e., sharper, than the Mk II in macro range. I used both with the Canon 500D achromat close-up lens. Works extremely well, the Mk I goes to 1:1 with it, the II to 1:1.25, higher magnification IOW, but the Mk I is sharper at these magnifications.

Kind regards, Wim