Originally Posted by
Dave Humphries
Hi Christina,
I have found that greater familiarity with my camera allows me quickly select the most appropriate method for the pertaining conditions.
I would guess that I shoot about 45% of the time AF-ON (back button focus), 45% AF-C with normal half press shutter press AF and 10% using other modes, including Live View and Manual Focusing.
AF-ON does remove a lot of the need to manually focus (as Dan says), or mess with switching the lens from M/A to M, which for me usually means losing sight of the subject while I fumble to feel for the switch.
AF-ON certainly doesn't suit all situations*, but it does make life so much easier for others (when you and the subject are not moving relative to each other), so locking focus (by simply lifting your finger of the button) is just one less thing the camera has to do, so less chance of a wonky aim, where the focus point misses the subject, giving a soft shot. If I find the mental workload of co-ordinating two fingers to separately focus and expose is too much, I switch to normal mode - I do this so often that it is usually top of the "recent" menu and easy to find.
* examples when AF-ON is great; shooting wading birds in water, perched birds (especially if 'inside' a bush/tree), landscapes, architecture, animals being shot through glass, mesh or wire fencing or bars (think zoo)
* examples when AF-ON isn't the best choice; flying or moving things - birds, insects, aircraft or trains (non-exhaustive list - you get the idea)
Regarding focus points, probably 95% of the time it will be a single point, for perched wildlife/landscape/architecture, I will compose and select one near what I want sharpest. 5% of the time I might try other modes, like Dynamic 9 or 21 point. or 3D, for flying things against a clear blue sky (be they birds or aircraft).
Hope that helps, Dave