What you see is not what you get. When it comes to shooting with a SLR camera, this is usually true. The camera keeps the lens at its widest aperture for metering and focus operations. It only stops down the lens to the aperture you want when the shutter release is pressed to take the picture. This is typically desired because the viewfinder would otherwise be too dark and the auto-focus sensor would have trouble acquiring focus.
The problem is that the depth of field (DOF) is directly related to the lens aperture. How could the photographer know if the end result will have the subject captured in acceptable sharpness before taking the picture? To solve this problem, most SLR cameras are designed to have a depth of field preview button that allows the photographer to stop down the lens temporarily to preview the depth of field. Is depth of field preview the only function of this button? Read More…
