Focus points for moving subject - DSLR WA setup

[Safety Stop]

I did a few tests with my camera using my Tokina 10-17 on moving subject, such as Sea Lion and would like to know your comments about it. I set the focus mode on "C" (never auto) but not on a single point (9 or 21 instead). About you, what is your prefered way to do it?

Envoyé de mon SM-T310 en utilisant Tapatalk

 

[Diver Dave1]

One option is to switch the focus control from the shutter trigger to another button and use auto focus. Then focus in advance at your desired distance. If you are shooting the 10-17 with f8 or above, you do not have to focus too far from the dome to have the entire background in focus.
If a sea lion comes up really close, just flick the 'new' auto focus button and it is in focus. Then when they back off, you can re-focus again.

A concern is having the camera focus on a particle in the water when you are after the fast moving subject. Separating the focus control and shutter control helps eliminate this issue.

This approach is how this photo was taken. Sailfish can travel over 60 mph and the water was not all that clear so focusing on particulates was a concern.
http://www.shiningseastudio.com/Und...antas/28350767_WH3hFx#!i=2401424489&k=wBMMvGP

 

[SeaInFocus]

I agree with kcmayes1. Back-button focus (using the AE-L/AF-ON button) is a great way to utilize the flexibility in your system's autofocus functionality. Personally, I rarely leave auto-focus up to chance and use single-spot focus as opposed to group auto-focus. I prefer AF-S as well, especially when trying to focus in low light conditions.