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While traveling the gravel roads of the Ft. Pierre National Grasslands we came upon many Upland Sandpipers. Using the car as a blind we were able to drive right next to them as they perched on one of the thousands of fence posts. The bird in this example was unfazed by our presence so I thought I would do a little Depth of Field (DOF) experiment. DOF is the distance between the closest and farthest points that are in sharp focus. For those that would like to see the DOF calculated for your lens/camera at various distances check out the DOFMaster website.
DOF in a photograph is determined by the Aperture (or ƒ-stop) setting of the camera’s lens (the camera tells the lens how large or small the opening is). The smaller the ƒ-stop number, the wider the Aperture opening is, and the narrower the DOF field is. The smallest ƒ-stop my Canon’s 100-500mm lens can go is 4.5.
One of the outcomes of using a small DOF is that when the bird is in focus, the background becomes blurry, which is called bokeh. Many times when I refer to a Great Bird Pick someone shares as having a “creamy” background it means that the background lacks any definition – it’s just a blur, and doesn’t draw the viewer’s eyes away from the bird.
Back to our Upland Sandpiper example. The first photograph below was taken with the ƒ-stop set to 7.1, which a relatively narrow DOF. Note that the grasses in the background are very blurry (out of focus).
Now look at the next photograph. Same bird but this time I changed the lens to an ƒ-stop of 13. At that Aperture the DOF is much bigger – not big enough to bring the background grasses into good focus, but there is more definition to them. The background is less-creamy than the image above. The top picture has a better bokeh.
Some of our members like a very creamy background so they will try to use the smallest DOF they can; I for one don’t mind seeing some definition to the background once in a while because it can give some context to the picture. In the examples above I kind of like seeing the grasses behind the bird in the bottom photo because it emphasizes where we were (National Grasslands). Play around with your ƒ-stop once in a while and see what effects you can bring into the image.
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Both great pics!