Thanks for all the replies. The penny still fails to drop. It will one day, I hope. Currently either I do not know something or brain cells not working.
Perhaps soon I will have an 'ah ha' moment. Waiting.
sanj....your wrote "either i don't know something or"...could it be that you don't know that one shot is better(sharper)than servo for "non action" shots? I'm sure you know this but I just thought i would point it out just in case. (i'm sure you do know because i've seen your awesome images)
the main reason for wanting the set up steve describes is to quickly and more easily switch from servo to one shot by having the buttons right next to each other. ("af-on button" and "*" button) (servo and one shot)
Northstar: No I did not know that 'one shot' is sharper than servo for still objects. I thought is was about getting focus, not the way one got focus. And I believe that once I get focus and I remove the thumb from the back focus, I am as good as 'one shot'. Am I wrong?
Having said all of this, I am positive that I am missing something... I will get it one day and go 'yeyyyy'.
Hi Sanj...I believe the "predictive" nature of AF servo leads to a lower hit rate on critically sharp images vs one shot...at least that's been my experience.
Even if you acquire focus with servo and release the AF-on button like you wrote, the focus was acquired using the predictive algorithms that servo uses. The servo system works great most of the time, but if something truly isn't moving, it's better to not have the predictive nature of servo involved.
If I'm wrong about this then someone please tell me.