Being a professional or an aspiring photographer, you must have heard at least once that the center focus point is the most accurate. It is true and is one of the major reasons why we prefer using the center focus point to click most of our photos.
You might not always prefer keeping the subject in the center of the frame, so you must have been focusing on the subject using the center focus point and then recompose the frame as per our desire. Do you realize what happens when you focus and recompose your frame by moving your camera?
What happens when you Focus and Recompose?
If you look at the diagram below, initially you frame the scene in such a way that the center focus point is on the closest eye to the camera. Once it happens, you lock the focus on the eye by half-pressing the shutter release button and thus also forming a parallel focal plane (blue line). Anything lying on this focal plane would be in focus, assuming that angle of the camera does not change.
Now in order to recompose the frame after focusing on the eye, you will have to change the angle of the camera but the distance between the camera and subject remains the same. So what happens is that as you move the frame downwards the focal plane shifts ahead as well. The focal plane that was earlier parallel to the closest eye has now shifted towards the nose. Thus, this will result in a photo which will have the nose in focus instead of the closest eye.
There are few factors that affect the amount of depth of field visible while using ‘focus and recompose’ technique such as the Focal Length of the lens and the Aperture value. The longer the focal length and the smaller the aperture value, the shallower would be the depth of field as you recompose the frame. On the other hand, the shorter the focal length and the higher the aperture value, the deeper would be the depth of field as you recompose the frame.
When to and when not to use Focus and Recompose technique?
In case your are shooting with longer focal length or smaller aperture value, always try and avoid using the focus and recompose technique. Shallow depth of field will give you out of focus photo even if you move the angle of your camera slightly.
But if you are shooting at short focal length or using high aperture value then you can consider using the focus and recompose technique as the focus shift would not be visible that much. Though if you do not want to take any risk with the quality of output, avoid practicing focus and recompose technique.
There might me situations when you do not have time to select the focal point manually, instead of focus and recompose technique you should simply click the photo keeping the subject in the center of the frame. You can always crop the photo during the post processing stage.
How to focus manually on a subject placed off-center?
If your subject or a part of the subject that you wish to focus on is placed off-center all need to do is to manually select the focus point from your camera. No, you do not have to manually focus using your lens, but what I mean here is that you will have to shift the focus point manually using your thumb/finger. In order to do so, you will have to shift the focusing mode in-camera from automatic selection to manual selection. Then using the joystick or the arrow keys you will have to shift the focus point at the desired position, keeping in mind that the focus points cover around 60-80% area of the frame.
Here I am sharing few images clicked using manual focus point selection, instead of using the focus and recompose technique. The main reasons being the use of 50mm lens and aperture value of f/1.4, focus and recompose technique will completely fail in this situation.
Never avoid using other focus points, yes the center focus point is the most accurate but the other focus points are fairly accurate as well. Throw away the lazy attitude of moving the focus point manually and trust me you will start witnessing the difference in your photos.