Listen up class. Photo 101 is in session. This sunflower image was a quick grab shot I took with a Canon 70D and 100-400 IS zoom telephoto lens at 400 mm, f5.6, to illustrate creative use of depth-of-field or depth-of-focus.
By opening a lens’ aperture or f-stop (from f22 up to f5.6 or f4 or f2.8, etc.) you decrease the area (front to back) that’s sharp. Setting a lens aperture (f-stop) wide open (to its lowest number like f2.8) minimizes this area of focus. Note how the yellow ray petals are out of focus but the interior disk flowers (those tiny yellow tips near the center) are sharp. I created this effect in order to draw attention to these otherwise inconspicuous flowers. It’s pretty hard to get noticed when you’re competing with that bright rim of ray petals. Even with these ray petals out of focus, one has to look hard to even notice the sharp little disk flowers. By the way, these are the real flowers that turn into sunflower seeds. The dark brown ones encircling the yellow ones have already been pollinated and are busy fattening into seeds.
You should be able to see your lens’ aperture change size by looking into the front of the lens as you turn down the f-stop dial. You’ll need to press your camera’s depth-of field preview button while doing this. Alas, not all cameras have this button, especially the “amateur” models. Today’s emphasis on “idiot proof” cameras makes understanding the principles and procedures of photography more difficult to understand. Hang in there and bear with us, keep studying and it will all come clear some day. If you’re like me, it’ll take you some time to figure all this stuff out, but once you do, your photography will improve markedly.
By the way, longer focal length lenses (telephotos) also minimize depth-of-field. They can be used to isolate subjects from busy backgrounds so they really grab your attention. We’ll explore this performance aspect in our next Photo 101.
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