Back button or thumb activation of autofocus is a setting that is available on most cameras and is often discussed on the Wetpixel forums. Alex and Adam chat about when they use the mode and how using, or not using it helps them to get their subjects in focus.
On Wetpixel Live, Wetpixel Editor Adam Hanlon outlines how cameras achieve autofocus underwater and presents an argument that a camera’s ability to achieve autofocus is one of the most important criteria that should be considered when choosing a camera for underwater use.
ZY Productions has posted a video on YouTube explaining how phase detection autofocus (AF) works. Phase detection is only available in SLR cameras, as it requires a dedicated AF sensor and a translucent section of the camera’s mirror, which are both components you will not find in a mirrorless camera. AF is a key camera function in challenging underwater photographic environments.
Wetpixel presents a round up of tutorials and information about using back button autofocus (AF) activation. Most SLR and top end compact cameras now offer this option. By decoupling the AF and shutter release, images can be recomposed and if autofocus tracking is also used, subjects can be tracked as they about within the frame.
Steve Perry of Backcountry Gallery has posted a tutorial on troubleshooting problems with autofocus. The 14 minute video covers issues with lens calibration, dirty AF sensors, wrong AF modes, AF guide inaccuracy, heat refraction, using the wrong AF point, dirty lens contacts, and poor technique.