By Stokley Wilson
This month's tip will discuss a very "in depth" subject: Depth of Field. There are many references to determine the exact depth of field. These books are available at many sources. I have been unable to remember these formulas, let alone use them in the field. Therefore, I have found alternative ways to extract maximum depth of field.
The easiest method to get maximum depth of field, I found, is to use the depth of field scale imprinted on the lens you are using. To find this scale, look at the focusing distance indicator on the lens. Towards the front of this indicator is the focusing scale of the lens. On either side of the focus point indicator is the depth of field marks for the different apertures of the lens (f4, f5.6, f8, etc.). Next, for maximum depth of field, place the infinity mark (looks like a lazy 8) on the smallest aperture mark on the lens. Then look at the other aperture mark on the other side of the scale. This is assuming you use a fixed focal length lens. If you are using a zoom lens, you probably don't have a depth of field scale imprinted on the lens, and you can use the next method.
The depth of field preview is a method to use for previewing the depth of field. This feature allows you to stop the lens down to the shooting aperture. The problem with this method is the image is very dark.
To combat this problem, I move my camera vertically, to maintain the same focusing distance from the subject, so that my foreground subject is positioned with the sky behind the subject. Now I can see the sharpness of the edge of the foreground subject against the much brighter sky. If the edge of the foreground subject looks sharp, then the rest of the subject will be sharp as well. The same method can be used with the subject at infinity. Look at the edge of the object against the sky, if the outline looks sharp, then it will be in focus in the photograph.
Now, if you own a Canon EOS camera with the "Depth Mode" feature, your job will be much easier. This exposure mode allows the photographer to define the near focus and the far focus to the camera. The camera then will set the focus distance and the lens opening to deliver the depth of field specified by the photographer. The camera can remember the formula, and can use it too. Rat, computers at work again.
Thank you for your interest,
King Photo Supply