What is the main difference between using a button to focus, recompose, and shoot, and focusing with a slight press of the shutter, recomposing, and shooting — just a slightly quicker release of the shutter when it comes time to press it??

Sorry I’m asking so many questions on your Erykah Badu set — we can move this to email, if you’d like… (although I think most questions may be answered?? haha)

This allows me to activate focusing separately from shutter release.

So, I can focus using continuous, let go of the button, recompose, shoot, and then go back to tracking the subject.

I find it very useful to focus in this manner especially when trying to shoot constantly moving subjects like Erykah Badu.

In answer to your question, I try to go up to f/4 as much as possible, especially when shooting the Canon 70-200mm. This is for two reasons.

1)The lens is quite soft at the 200mm end and I feel that stopping down, even a little, helps resolve more detail

2)I do not trust the continuous focus (AI-Servo) accuracy of the Canon 1D Mark III. I’ve shot with the body/lens combination before and it has regularly failed me when at f/2.8. The greater depth of field achieved by f/4.0 compensates for focusing errors.