Depth of field is what gives your photos their “focus”. Not just what you are focused on, but what your eye is drawn to. Depth of field is like taking a marker and circling what you want the viewers eyes to be drawn to. Here are two photos of the same subject, taken from the exact same vantage point, they went through the same post-process in Adobe Lightroom and were shot on a tripod. The only change was the f/stop (we will come back to that).
The first image is a shallow depth of field.
Look at the photo – where is your eye drawn? To the Nikon 35mm lens in front. The other lenses form a background to the image, helping to tell the story, but you eyes tell you that the star of this image is the lens in front. Now look at the second image.
The story you see in this image is different. All six of the lenses are part of the story. When shooting people, the same technique holds true. Have you ever looked at a typical portrait that has been shot with a “point and shoot” type of camera and felt like the subject blended in with the rest of the photo? If the background is in sharp focus, then the subject of the photo shares the image with the background. If the background is soft due to a shallow depth of field, your eye is drawn to the subject.
How do you control depth of field? There are several factors that play into depth of field, in this example it was by only adjusting the aperture, called setting the f/stop. In the two images above, the settings were as follows:
Camera: Nikon D3100
Lens: Nikkor 60mm Micro (Macro) f/2.8
The shallow depth of field was shot at 1/10 of a second at f/3.0
The deep depth of field was shoat at 1.3 seconds at f/14
The shallow depth field had a wide open aperture allowing a lot of light to hit the sensor quickly allowing a faster shutter speed. The deep depth of field had a much smaller aperture requiring a longer exposure time for the required light to reach the sensor. The easy way to remember this is “big number, big detail; small number, small detail.” In the example above, the shallow depth of field was achieved with a small f/stop.
There are two other important factors that play into achieving the desired depth of field. The first is the relationship of the subject to the background and the photographer to the subject. The second factor is the focal length of lens you are shooting with. For more information about how these factors impact your depth of field, here is a great video! Mark Wallaces teaching makes what can be a difficult topic much easier to understand. He shows a series of photos in which he achieves different depths of field by changing each of these three factors.