Controlling Depth of Field

Depth of field study.

*****

By Keith Birmingham

One of the basic subjects that I struggled with as a “beginner” in photography was controlling my “depth of field“, and thus controlling the sharpness of my photographs. It is one of those rules that can easily boggle my mind trying to keep it straight. When I first purchased my camera I carried it around with everything set for “automatic” exposure. That way I would not have to worry with so many of the questions that zoomed through my mind if I had to worry about getting the correct exposure. However, I soon realized that I was getting “a” correct exposure, but not “the” correct exposure. I was getting what I wanted in some parts of my photographs, but not with the entire images. For instance, in scenes that covered a large area there were objects closer to me, or further from me, that were out of focus even though my main subject was in focus. Research taught me that controlling my “depth of field” was very important in getting the visual results I wanted.  What  is in focus in a photograph is very important to creating the mood, or meaning of a photograph.

What I realized was: when you change your aperture setting you change the “depth of field”. That is, you change the area of the photograph which appears to be in focus in a photograph.

Here is how to get the results you want:
    1.) Large aperture = smaller f/numbers = produces limited depth of
    field.
        Larger hole = f/32 = limits depth of field.
    2.) Small aperture = large f/numbers = increase depth of field.
        Small hole = f/2.0 = decreased depth of field.
    3.) Use a smaller aperture number to decrease depth of field.
    4.) Using a smaller aperture number makes the aperture opening
    larger and requires that you use a faster shutter speed to get a correct     exposure.
    5.) Use a larger aperture number to increase depth of field.
    6.) Using a larger aperture number makes the aperture opening
    Smaller and requires a slower shutter speed to get a correct exposure.

Here is how I now remember the rules:
    1.) Large hole = less depth of field.
    2.) Small hole = more depth of field.
To make it even easier for me I only try to remember one rule: The other rule works if you just get one right: ).