Have you ever shot in single focus mode and you can swear your focus was locked on but when you looked at the image it was out of focus? Let me try and explain how single focus mode works and how you can use it properly to get tack sharp images.
For the purpose of this quick tip were only discussing focus, not exposure which is equally as important.
Before I fully break down single focus lets look at the focus modes you may encounter. For the most part you have single focus, continuos focus and manual focus.
Single focus is best used when your subjects are not moving such as portraits, landscapes or still lives. The idea behind single focus is that you hold the shutter button down until your focus locks on your subject. At that point as long as your finger is held half way down on the shutter button your focus will not shift away from where it locked.
This is a good thing when your not shooting moving subjects like i said above. Where some people run into issues with single focus is they lock the focus than they move or their subject moves. When this happens your focus is no longer going to be spot on from where you locked it. When the focs plane changes either by you moving or your subject moving you have to refocus.
Some tips to keep in mind are once you are locked in do not move forward or back. Try to keep the same focal plane and if you or the subject moves be sure to re focus. Depending on your fstop setting if you shoot at a higher number such as 8, 11, 16 you give yourself more leeway for movement.
But my major tip is to always re focus if you or the subject moves. One last tip is to focus on the subjects eyes opposed to focusing on their nose or forehead. This is best done in single focus where you focus on the eyes than recompose your image to where you would like it all without changing your focal plane.