What Is a Preview Button and How Is It Used in Photography?

When talking about cameras and taking photographs a ‘preview button’ is a button found on most cameras which allows the shooter to preview the depth of field that will be captured at the current aperture setting. When you look through a camera viewfinder you see a view of the scene with both the foreground and background in focus. This allows a shooter to compose an image accurately but does not show you how your aperture settings will affect the depth of field. Depressing the preview button, usually found next to the lens mount on a camera’s front plate instructs the lens to stop down the aperture diaphragm to the currently selected f-stop, allowing you to see the effect this has on depth of field directly through the camera’s viewfinder.

The preview button on a modern DSLR