Finding and using the Depth of Field Preview Button

Just because things appear one way through your viewfinder... doesn’t mean that’s how they’re going to appear once you press that shutter button. Unless you use your DOF preview button religiously and learn to truly dial-in your depth of focus ... you will never be the artist you know you can be.

Your digital SLR camera employs an automated aperture system that keeps the aperture (hole) open as wide as possible (no matter what aperture has been set in-camera) until the shutter button is depressed. Then (and only then) does it shrink the aperture to what the photographer has dialed-in — giving him his desired depth-of-field in the final image. Since the aperture is always wide-open you are NOT seeing the world (depth-of-field-wise) as it will appear in your final image when looking through your viewfinder. YOUR CAMERA IS LYING TO YOU.

To get a ‘preview’ of what the depth-of-field will actually be, YOU MUST depress the DOF preview button. This important button disengages the automated aperture system allowing the aperture to shrink to what you’ve dialed-in — giving you a ‘preview’ of how much focus you’ll achieve in your image. Without the use of this button (or the use of a DOF scale - now taken off of most lenses) you WILL NOT KNOW the true depth of field you’ll achieve. This makes the depth-of-field preview button the single most important button on any camera — if you actually care about what’s in focus and what’s not.

To really see the truth, TRY THIS: Set your aperture to f/22 (a very small hole) and turn your camera around with your lens facing you. Hold the back of your camera up to a light. Look at the aperture size itself through your lens. Notice how large it is. Now, with the camera still turned backwards depress the depth-of-field preview button.  

When the DOF preview button is depressed the size of the aperture shrinks dramatically. This means the viewfinder can not be trusted for focus information ... unless the DOF preview button is engaged or you are using the largest aperture in your lens.

Finding the Depth of Field Preview Button

The location of the depth of field preview button moves around quite a bit between camera manufacturers. On Nikons (top photo) look for it on the lower right side of the camera. Canon owners should look for it on the bottom left side of their camera (bottom photo). Other photographers may want to consult their camera manual if the location is not apparent. If your camera lacks this option, if you don’t have a depth-of-field preview button ... get a new camera. An artist (or even a semi-conscience photographer) can’t live without it. If he can and does... then maybe he really isn’t as good as he thinks he is. How can focus depth not be important to think about or to make a priority?

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