By Anna Chan
The depth of field in a photo is the closest and furthest distances which are in focus. Once a certain point is focused upon, a distance in front of and beyond that focused point will also be in focus. This range is determined by the f-stop used. The lower the f-stop value, the less the depth of field. For example, an f-stop of 2.8 will have a very shallow depth of field, where as an f-stop of 8 will yield a greater depth of field.
Using the current settings on the lens in the photo to the right, the object intended to be in focus is approximately 0.8 meters away. The f-stop 11 is painted a yellow, corresponding to the yellow lines by the focusing ring. This indicates that the distances which fall within the yellow lines will also be in focus. In the case of the lens, the space that is about 0.7 meters to one meter away will be in acceptable focus.
Depth of field is commonly used to highlight an aspect of a photograph. The eye is naturally drawn towards the sharpest object in a photo. This is the example in the first photo of the two candles. Set two metres apart, the candle on the left is in complete focus. This is where the attention is instantly drawn. The candle on the right, though not in focus, is still recognizable as a candle. Its placement creates a depth, making the photo interesting to look at.
Had the candle on the right also been in sharp focus, the two would compete for attention. This confuses the eye. Shooting at a high f-stop will result in a high depth of field. When there are too many sharp images within the photograph, it becomes disjointed and unfocused–in terms of attention. There are too many elements to look at.
However, this effect can be desirable in certain situations, such as photographing landscapes or portraits.
Alternately, a lower f-stop will give results similar to the second photo. With the same set up, the candle furthest from the camera is barely recognizable. This makes the candle on the left the obvious subject.
There may be a point where the objects out of focus can become too distracting. An argument can be made that the glowing blur in the second photo is distracting to look at, upstaging the candle on the left.
Remember, when you adjust the f-stop to achieve the desired depth of field, keep in mind the shutter speed will have to be adjusted accordingly in order to maintain a proper exposure. Make sure your shutter speed doesn’t fall below 60 as the photo will begin to register hand-shake. When using shutter speeds slower than 60 use a tripod to eliminate a blurry photo due to hand-shake.
Contact me at anna@gauntlet.ucalgary.ca if questions arise.