Manual Focus

[Overread]

Out of interest does your lens have HSM/USM type focusing motor (ie the kind that has all the time manual focusing even when in auto focus mode). If it does you can make use of the backbutton auto focus control method.

This works by shifting your auto focus off the shutter button and onto a button on the back of the camera body (most DSLRs have thus feature- some have a dedicated AF button on the back whilst others have the function replace something else).
This means that instead of AF starting when you hold the shutter down, it only starts when you hold the backbutton down (with your thumb). This means that you can use the continuous AF mode and if the AF is failing you on getting a lock on your subject you just release your thumb over the back button and manually focus - this is without having to fiddle around to find the AFon/off button on the lens and also means that AF can make a quick ballpark area focus lock on before you manually correct the focus.

 

[Ron Evers]

I use manual focus almost exclusively with legacy lenses on a modern camera without prisms or mirrors. I shoot mostly nature/wildlife & appreciate how frustrating auto-focus can be.