Every photographer needs to understand depth of field.
Most do get to grips with it. However, when working with a shallow depth of field many photographers misjudge the depth they have to work with. Here is how to work it out.
All too often when using a shallow depth of field the edges of the sharp/bokeh region are well defined. If you get that boundary in the wrong place it is quite easy to spoil the image. For example if you take a portrait with a wide open aperture and the depth of field is too shallow you might find that the eyes are in focus. However, the ears are out of focus and so is the nose. A disconcerting picture! So how do you get over this? Find out by deliberately working at the wide-open aperture end of the range. Push yourself. Open up to a wide aperture and keep it opened up until you feel comfortable you have got control.
Setting it up
Setting your lens to the wide end is easy. Just open up the lens until you have the smallest f.number showing in your screen or viewfinder. Most photographers will have one lens with an f3.5 or f4 aperture (or less). It is possible to buy lenses with much wider apertures. So you may have as much as an f1.2 aperture – which will give you a very shallow depth of field.
Once you have your lens at the wide open position you keep it there. Then go shoot… a lot.
I know this may seem a tall order but it is fun. Keeping a fixed depth of field dictates much of your perspective on a shot. In order to create nicely composed pictures you will need to move around a lot. You will want to keep your subject sharp. Photographing a range of different sizes of subject means you need to move back and forward to vary the depth of field to fit the subject.
If you take a picture close to you, with a shallow depth of field you will maybe have less than 100mm of sharpness – or much less depending on your lens. If you take a picture focusing at 2 meters from you may find, say, 300mm (12 inches) of sharpness – enough to fit a head into and keep it sharp. If you are working at say 200 meters you may be looking at a really quite wide depth of field – maybe several car lengths.
The point of the exercise is that holding the depth of field fixed makes you walk around and gain experience with your lens. After a while you will be able to judge how much depth of field you will get when shooting at a particular distance. Then you will have mastered your lens at the wide aperture end of the scale.
Getting good control of depth of field is really helpful
You begin to have much more creative control when you have good depth of field control. If you can get you subject finely focussed and sharp – but everything else in a beautiful soft bokeh – your subject will really pull the viewers eye into the shot. Depth of field is all about isolating your subject and making everything else less of a distraction. Control is everything.
Once you have gained control of the extreme end of the open aperture, you can move on. Now make the aperture one less stop open. Do the same exercise. Get to know your lens at this aperture/depth of field combination. Once you have mastered that, move up another stop.
After a while you will have complete creative control over your use of bokeh and the depth of field. An enviable position… you can really be creative when you have such control.