Depth of what?
In photography, we often talk about depth of field. Before getting to the heart of the matter, let's define this.
First of all, let us simply state that the depth of field is the sharpness area in front of and behind the subject for which you carry out your main focusing. For instance, for a subject that is five meters from your camera, the depth of field area could be between 1 meter and 40 meters for an aperture of F11.
The smaller the lens opening, the larger the sharpness area. To better understand what I'm saying, have a look at the three pictures below. Three objects are placed at three different distances and photographed with a 200-mm telephotographic lens. In the first image, taken at F4.5, only the subject in the foreground is sharp. In the second image, taken at F11, the second object placed in the middle ground is also sharp. In the last image of the series, with an aperture of F32, all three objects are sharp.
Be Careful What Lens You Use
The higher the millimeter number of your lens, the shorter the depth of field. With the same aperture, it is easier to have greater sharpness at all distances when you use a wide-angle or normal lens than when your pictures are taken through a telephotographic lens. If you want to obtain the same depth of field with a 135-mm telephotographic lens as with a normal 50-mm lens set to F8, you will have to go down to F16.
What Difference Will This Make on My Photographs
When shooting your photographs, the depth of field can be your ally or your worst enemy. You may only have wanted to get a snapshot of your child in the foreground, but all your family members and the entire background setting are as sharp as your major subject. Or perhaps you wanted to take home a picture of the superb Rockies with, in the foreground, the edge of the wharf and the boats, but only the latter were sharp-and the background blurred. Both these situations could have yielded winning results had the depth of field been properly controlled.
In the first case, i.e., the photo of your child, you should have focused on him and set the aperture to a wide F2.8. This would have reduced the depth of field, and only the major subject would have been sharp, thereby isolating him from a blurred background.
As far as your traveling souvenir is concerned, you could have obtained sharp pictures of the wharf, boats and background all at the same time. You should have reduced the aperture to F16 or F22, depending on the lens used, to increase the depth of field.
Should You Choose ''Autofocus'' or ''Manual Focusing'' ?
Is your camera ten years old? No problem! You control the situation because focusing is manual; you are the one deciding on the sharpness area. However, for action, sports or live shots, autofocus would be most useful.
Is your camera recent and does it have a built-in automatic focusing system? In this case, you decide... nothing! You've lost all control! Well, not quite all. There are a few settings available to let you find a compromise, and this lets you make a number of decisions.
Certain models allow you to lock your focus on a given subject and return to your framing or to your selected composition without affecting the other elements arranged at various distances in the picture. Several lenses also offer the possibility of going from « autofocus » to « manual mode » by disconnecting the electronic focusing mechanism.
Now that you control the focusing, you can also control the aperture. With your old-fashioned camera, still no problem, everything is manual!
With recent cameras, however, it is impossible to really control the depth of field, because most automatic mode programs randomly manage and combine speed and aperture to provide perfect exposure.
This is when the « aperture priority » mode available on most major reflex camera adjustment knobs comes to your help. With this mode, you select the aperture yourself, and the light meter automatically compensates with a speed corresponding to the right exposure for the film used. This way, you don't lose the automatic exposure when you control the sharpness area you want to obtain.
Controlling the depth of field allows you to create pictures that tell a story. The subject may be isolated to emphasize its character, and landscape shots can be spread out to show their entire splendor. Together with a good choice of lens, controlling the depth of field allows you to be creative and always looking for new pictures.
As it turns out, in photography, depth of soul is much more important than depth of field...
Go for it, and Happy Shooting!
With the cooperation of Jacques Bourdages, PFE.