Unclehaggz wrote:If your talking about Focusing for Light painting in the dark, I usually shine a torch at the distance I want to be away from the camera, half press the shutter button so the camera focus's on the illuminated area, then turn off Auto focus whilst keeping the shutter button half pressed. Then locked by using the switch set to manual focus, leave the lens well alone and take picture as per normal, review your shot and check clarity/focus, adjust as required and/or re focus using the above technique.
Also if doing long exposures, I find turning off image stabilization (Canon) and/or OS (Nikon), improves sharpness as the lens isn't trying to make adjustments whilst moving lighting around, hope it makes sense.
Hope it helps
UH
+1, I use exactly the same technique!