For this blog I thought I would say a few words about how to control an image’s depth of field. In other words how much of the photograph appears to be in sharp focus. This is a really important skill to master because it opens up so many creative possibilities.
Lens choice will affect the DOF of your photograph.(wide angled lenses produce a larger depth of field than telephoto lenses)
The aperture selected will also affect the image’s DOF. The larger the aperture, the smaller the DOF. For example, F2.8 will result in a much shallower DOF than F32 which is a smaller aperture . An easy way to remember this is that a large F number results in a large depth of field and a small F number results in a small DOF.
POINT OF FOCUS
The third thing to affect DOF is where you focus within the image. The further away you focus, the greater the DOF. Although, if you focus too far into the image, elements within the foreground (front of the image) may start to lose focus. It is a good idea to experiment with different points of focus from the same viewpoint and access how they affect the image’s DOF. You can do this by either accessing the image on your camera’s monitor (if digital) or by using the DOF preview button on your camera. For maximum DOF for a given aperture, focus a third of the way into the scene. This will keep the foreground in focus as well as giving maximum sharpness to the background. (The amount of the image in apparent focus extends a third of the way in front of the focus point and two thirds behind it.)
Gaining maximum DOF by focusing a third of the way into a scene is a good starting technique. It will serve you well for the majority of situations. However when DOF is really critical (ie when you have a foreground object that’s really close to the camera that you want to keep in sharp focus as well as some far away background detail) a more accurate technique may be required. Using a DOF scale and hyper focal focusing is a very precise way of ensuring maximum DOF at any given aperture. I cover this technique in my advanced photography course.
NOTE : APPARENT FOCUS
There is only one point of the image that is complete focus. Apparent focus is the area of the image that also appears to be in perfect focus. In reality this area is not in perfect focus but it is so slightly out-of-focus that the human eye cannot distinguish between the two.
CAMERA TO SUBJECT DISTANCE
Lastly, how close the camera is to the subject will have a bearing on the depth of field. The closer the camera is to the subject, the shallower the DOF will be. That is why when macro (extreme close-up) images are taken the DOF may only be a few millimetres.
By controlling all four of these variables you will have complete control over the DOF of the photograph you are taking.