Understanding Depth of Field
To determine what’s in focus (Depth of Field) and what is not in focus (Blur), the photographer must consider 3 things:
1) Aperture setting
2) Focal Length of the lens
3) Distance the Photographer is to his/her subject
Longer lenses (200mm and longer) tend to give a very shallow depth of field (less space in focus). To further complicate matters, the farther away the photographer is to her subject, the more depth of field; or the more space you will have in focus.
Aperture Settings for Background Blur
Luckily, long lenses and long distances between photographer and subject are pretty common scenarios for bird photographers. That being the case, you just have to determine what aperture to use to achieve a good balance of subject in focus and background blur.
The Impact Aperture has on Photographs
A friend of mine asked how I pasted in the beautiful blurred background on my bird photographs.
HOGWASH! There is no emoticon to express how I felt when I heard that.
Understanding aperture is the cornerstone to achieving creative control of your photos. Aperture is measured in “F Stops”, and is the size of the opening in the lens that the photographer sets before a picture is taken.
Larger apertures produce more background or foreground blur and less space in focus. Smaller apertures produce greater depth of field, or more space in focus. If there are multiple subjects on which to focus and these subjects are not the same distance from the photographer, the depth of field needs to be tightened up so all your subjects are in focus. Given the right light and lens, you can set your aperture so small that everything in the frame will be in focus; nothing would be blurred.
The Quality of Out of Focus Areas
A photography term to describe the quality of background or foreground blur is Bokeh. “(BOKEH = noun, a Japanese term for the subjective aesthetic quality of out-of-focus areas of a photographic image.)” Keep in mind that making a judgement on the bokeh quality of a photograph is highly subjective and hard to quantify. Generally, very pleasing Bokeh is a function of the lens. A very high quality lens will most likely produce a very pleasing Bokeh.
Achieving Balance in Your Photographs
You want to achieve a nice balance in your photographs. All of the subject(s) in your photo must be in focus and stand out from the background. The blurred background should be pleasing to the eye and not distract the viewer from the subject of the photo.