Tuesday, February 9, 2010
Master Depth Of Field
Learn how to place and control your depth of field for creative focus control
|ƒ/22—Focused on Fourth Bell
Where you place your point of focus is as important as your selected aperture for taking total control over your depth of field. Approximately one-third of the available depth of field for a given aperture will fall in front of your actual point of focus.
Depth of field (DOF) seems like a pretty straightforward thing, right? Photographers quickly learn that to minimize DOF (in order to isolate the subject from its surroundings for a simplified composition), we should use a larger aperture (smaller ƒ-number); and to maximize DOF (in order to ensure all the important details in a scene are tack-sharp), we should use a smaller aperture (larger ƒ-number). The basics may be simple, but to wield its full power, it helps if you can measure your DOF—or, more precisely—if you can position the zone of sharpness exactly where you want it.
ƒ/2—Focused on Fourth Bell
If there are particular items nearer or farther from the point of focus that you hope to place within the zone of sharpness—a landscape, for example, with items in the foreground and in the distance—it may be best to move the focus point. That’s right: Sometimes it’s best not to focus on the most important element in the scene. It all depends on those supporting details and where they sit in relation to the subject.
For example, if you’re photographing an approaching sleigh pulled by nine reindeer, you might choose to focus on the bright-red nose of the lead reindeer. The DOF then might extend all the way to the third or fourth reindeer (depending on the lens focal length, aperture and distance). But because the DOF extends into the foreground, too, you’re wasting part of the usable DOF on the area in front of the lead reindeer, where there’s literally nothing in the scene!
ƒ/22—Focused on First Bell
Check the math; get your hands on an old manual-focus 35mm film SLR and lens. The markings on the top of the lens allow you to measure how much of the scene will fall within the sharp DOF at a given distance and aperture. Maybe it’s because DSLRs with LCDs allow you to check your DOF right on the back of the camera, or maybe it’s because the DOF preview function is so simple to use, but most modern DSLR lenses no longer include this manual DOF scale.
Focusing one-third of the way into a scene doesn’t guarantee that the entire frame will be sharp. You still have to utilize aperture and focal length appropriately to maximize DOF. But for a given zone of sharpness, positioning it properly does mean that you won’t waste any available sharpness that the aperture and focal length provide.