One of the things that is fun to play with when taken photographs is Depth of Field, or DoF. DoF relates to the amount of the image that is in focus or appears to be in focus around the subject. The rest of the image may then fade to a blur depending on several factors or it may be "sharp" from front to back. Many landscapes will have large DoF so that the image is sharp all the way through. On the other hand, portraits and close-up photographs will have shallower DoF in order to draw the eye toward the subject and away from any distractions in the background; i.e, the subject will be sharp but the rest of the image will be blurred.
More after the jump.
To get a shallower DoF you can open up your aperture to as wide as it will go (small f/stop #). A smaller aperture (large f/stop #) will help get more of the image in focus. Zooming in to your subject can help narrow your DoF while using a shorter focal length will aid in getting more of the image sharp. The relative distance of your subject to the background is also important. If you are significantly closer to your subject relative to the background, then the subject will be in focus and the background will be more blurred. Conversely, if you stand farther away from your subject relative to the background, more of the image will be in focus. Of course you can use more than one of those techniques as well and it is a good idea to combine them for the best effect. Consumer zoom lenses, as an example, will usually not be able get an aperture wider than f/5.6 when zoomed all of the way out. This can give you more DoF than you might want and lead to background distractions. To combat that, set your aperture as wide as it will go (f/5.6 in this instance) and get as close as you can to your subject. Ideally you want to the background to be quite a bit further way from the subject than you will be to the subject. This will have your subject sharp, but the background fading off to a pleasing, non-distracting blurred field.
DoF is a property of photography that is used to help isolate the subject from the background as well as rendering a busy background less intrusive. Play around with DoF. It is can be a lot of fun.
Friday, September 11, 2009