Most DSLR cameras come with a built in depth of field preview button.
This button allows you to see exactly what parts of your image are in or out of focus. When you combine this button with an LCD screen it takes all the guesswork out of your aperture settings. Refer your camera manual to see exactly where this button is located on your camera.
We also have another video that will show you how you can make the most of the depth of field preview button and see how your aperture affects the photo you are taking.
