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Understanding Depth of Field

This is something which seems to cause problems for all photographers both beginners and experienced. It's not really that complicated so I have prepared this series of shots to help you understand the basic principles.
I laid out 6 items diagonally across a table so that they were all at different distances from the camera lens. The "Chocco Topping" was about 10cm away and the "Baresa Olives" about 40cm.
All shots were taken focusing on the "Chocco Topping". For the first shot I set the aperture (that's the hole that lets the light in at the sensor when the shutter is open) at f2.8. Remember the smaller the "f" number the larger the aperture and consequently the shallower the depth of field.
In each subsequent shot I increased the "f" number i.e. making the aperture smaller and you will notice that with each shot the depth of field increases, in other words more of the picture is in focus so the further away items to the left of the shot become clear.

You will also observe that as the aperture is made smaller by increasing the "f" number it is necessary to leave the shutter open for longer periods so that the sensor receives the same amount of light to ensure correct exposure.
So what does all this mean in practical terms? Select the "f" number to suit the picture you wish to take. If it's just a flat surface or a face for instance a shallow depth of field is just fine and there may be many good reasons why the background and foreground should not be "sharp" however if you are taking a scene of a beautiful valley you will want as much as possible to be in focus so a larger "f" stop is essential.
Always remember that as you increase the "f" number the shutter speed gets slower and if it drops below say 1/60th of a second you must stabilise your camera on a tripod or similar device but if the subject is moving depth of field may have to be sacrificed in order to get a crisp picture. Unless the light is brilliant it is difficult to capture a moving target whilst also retaining a lot of detail both in front of and behind the subject. You can of course raise your ISO level to help in that case but remember the quality of your image will suffer.
Life is full of compromises! Click on the first slide and watch the depth of field grow with each shot. Happy snapping.

Cameras with manual and semi-automatic settings can be set to "aperture priority" which means that the photographer sets the aperture size and the camera selects the appropriate speed or to "shutter priority" where the photographer sets the speed and the camera selects the appropriate aperture size. In this way the exposure remains correct as designed by the manufacturer of the camera.

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Depth of field (1)
Depth of field (2)
Depth of field (3)
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