Once you have learned how to control the focus and depth of field on your camera, when shooting stills or video. Here’s a few more advanced bits of information.
Some of this stuff, I know you know, you know you know, but there will be some things you know you don’t know. And hopefully some things you don’t even know you don’t know. ;)
Lets start with something relatively basic.
DEPTH OF FIELD PREVIEW BUTTON
Starting off with something simple, the depth of field preview button on most SLR cameras is usually on the front of the camera, near the lens. You may have noticed it and may have pressed the button to find that it doesn’t do anything but make the view in your viewfinder dark.
Most cameras nowadays, don’t actually stop down the lens diaphram or aperture until you click the shutter. When framing up your shot, and before you click the shutter, pressing the DOF preview button shows you what will and will not be in focus. Don’t be too concerned about the view through the viewfinder darkening when you press the DOF preview button. This is a side effect of less light coming through the lens and isn’t a representation of the exposure of the final image you shoot.
DEPTH OF FIELD DISTRIBUTION
Depth of field is not weighed the same for distances closer of further away from your subject. 1/3 of the range is in front and 2/3 is behind it. You can use this especially when shooting something like group photos, where rows of people are at different distances from the camera. Putting the focus back behind the first row, will help get more of the group in focus.
HYPERFOCAL DISTANCE
The hyperfocal distance is the closest distance at which a lens can be focused while keeping objects at infinity acceptably sharp. This is also effected by the aperture. As the aperture gets smaller the hyperfocal point gets nearer to the camera increasing the maximum depth of field.
You can find this on most prime lenses, you probably didn’t even realize that it was there.
These are f/stops arranged on either side of the critical focus mark. On the focus ring the distance scale in red numbers indicate feet and white in meters. Let us assume that we have the camera set to f/16. The focus indicator is pegged at infinity we see that on the right side of the focus mark the 16 lines up close to the 5 meter mark. Reading this scale tells us that focused at infinity with an aperture of f/16 everything from 5 meters to infinity will be in focus.
CIRCLE OF (LEAST) CONFUSION
Since there is no critical point of transition from in to out of focus, a term usually called ‘circle of confusion’ is used to determine how much a point needs to be blurred in order to be perceived as unsharp. The depth of field is the region where the COC is less than the resolution of the human eye, or of the display medium. This closely relates to the hyperfocal distance mentioned above.
