When shooting macro shots with a DSLR camera the depth of field or DOF can be extremely small. The DOF is the distance between the nearest and farthest objects in a scene that appear sharp in an image.
The DOF is influenced by several factors
- The closer the object in focus the smaller the DOF gets.
- The longer the focal length of the lens the small the DOF.
- The wider the aperture (smaller f-stop numbers) the smaller the DOF.
- The bigger the camera digital sensor the smaller the DOF.
To illustrate the impact of the aperture on the DOF I took the following series of photos keeping everything constant, except the aperture. I was using a Canon 5D Mark ii (full frame sensor), 100mm macro lens, focused about 6 inches from the water drops. Of course, the camera was on a tripod to eliminate any movement.
You can click on any of these photos to get a larger view and then flip though them using the right and left arrow keys.
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| f/22 |
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| f/11 |
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| f/7.1 |
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| f/4.5 |
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| f/2.8 |
You can see that even at a small f/22 aperture the depth of field is only about 2 inches. At f/2.8 it is about the width of one small waterdrop. Here's a crop of the f/2.8 shot where you can see just how small the DOF is.
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| f/2.8 cropped |
Understanding the DOF is important in all photography and critical in macro photography. In order to control the DOF you need to understand the factors that influence it and adjust those to create the composition you want. Choose the camera and lens combination that will get you in the range you want then adjust your aperture and distance to get that really cool macro.
Good article, but I disagree with your 4th factor that affects DoF. The sensor size has no effect on DoF. Think about it, the lens is focused on the "film" plane, the "circle of confusion" is what it is, regardless of the size of the sensor. Crop sensor is just that - a crop. Why/How could DoF be different? Now, I will say that when you use a FF camera, you have a wider field of view (with a given lens) and thus will (tend to) move in closer to the subject AND THAT will change the DoF. It's distance, not sensor size.
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