A camera can only focus at a single spot, at a point of distance. Areas in the front and the back of that specific point may appear to be acceptably in focus. This area of focus is depth of field. Deep depth of field means you have more areas in focused and shallow depth of field means you have less area in focus.
Let`s explore what affects depth of field and how you can improve your focusing technique.
How do you focus better?
You need to get out of automatic mode, if you want to improve on focusing. You want to have more control than auto mode. It may seem intimidating at first, but you will soon be more confident while finishing.
You need to know your lens
Practice until focusing becomes instinct to you. If the subject is moving away, you turn the focus ring to the left. If the subject gets close, move the ring to the right. You need to know the lens inside out, so your instinct knows the direction to turn the focus ring. Amateurs will start moving ring to the right and left in panic, but you don`t want to do that.
Why not have a go at practicing without looking at the monitor? Go around in circle of an object, get close and far away, and see if you can adjust the focus right without looking.
The distance from camera to subject matters. As you move closer to your subject, the area of the image that is in focus gets smaller.
As you pull back you will see more areas focused. It is when the subject gets closer or move far away that you will be adjusting the focus. So, naturally if you keep the physical distance on mind, you will not have to adjust focus too much.
Zoom into focus and then zoom out
If you are filming a person, one way to get him/her in focus is to zoom into their eyes and adjust the focus. Then zoom out. Your focus will stay on that person`s eyes plus whatever the depth of field. You want the most important part to be focused most, rather than at the corner of depth of field.
Aperture of f/3.0 is wide, while an aperture of f/20 is small. The smaller the aperture (High F-stop) will give you more depth of field. You have more area in focus. The bigger the aperture (Low F-stop) will give you less depth of field. You have less area in focus.
If you want to keep things in focus, you will need to adjust these settings. Just be careful because too high F-stop, i.e. small aperture, the image starts looking blur.
To increase your Depth of Field (make a larger Depth of Field, make more of your image in focus):
I hope this helps. I have found that getting out of auto focus has helped me improve a lot in my filming.
Practice, practice and practice!
I am a documentary/News cameraman based in London.