Thursday, 12 March 2009
Taking Portrait Photos with Blurry Background and Understanding Depth of Field
We have all seen beautiful photos where the object is perfectly focused while the background is blurred. Such a photo can be very dramatic and might seem to be hard to shoot. In this article we will give you a few tips on how to easily take blurry background photos that will impress your friends and family. You will also better understand what Depth of Field is and how to control it.
Depth of field (also known as DOF for short) is the most important thing to understand before shooting a blurry background photo. Depth of field is defined as the range in which the photo is in focus. For example an infinite depth of field means that the photo will be in focus from a certain distance from the camera and up to infinity. When taking a blurry photo the goal is to set the depth of field just around the object. In this way the object is in focus while the background behind it is not.
How do you control the depth of field? After all there is no “depth of field” menu in the camera (wouldn’t that be nice…). Depth of field is an optical figure that is influenced by a few factors:
The distance of the object from the camera:
This is obvious to understand when taken to the extreme. Shooting an object 10 feet from the camera will result in a smaller depth of field than shooting an object 100 feet from the camera. Obviously shooting an object which for all practical purpose is infinite distance from the camera will result in the camera focused on infinity and the depth of field being infinite too...
The wider the aperture (f number decreases) the smaller the depth of field and vice versa: the narrower the aperture (f number increases) the greater the depth of field. Just remember that the depth of field changes along with the f number: when the f number increases and depth of field increases and vice versa. Unfortunately you can not just change the aperture as you wish. Changing the aperture results in a need to change the shutter speed (either manually or the camera can most likely do that for you automatically). The wider the aperture the more light that penetrates the lens and the faster the shutter speed needs to be so there is a limit to how wide you can set the aperture to.
The focal length of the lens:
The shorter the focal length the greater the depth of field and vice versa the longer the focal length the smaller the depth of field. For example if you use normal lenses at somewhere around 50mm your depth of field will be much greater than if you use zoom lenses at 200mm. With long focal length the depth of field can be extremely small. For that reason zoom lenses are a good choice in order to shoot a good blurry photo that is practically focused only on the object.
After understanding the theory it is best to go to the field an experiment. You will get a sense of how your photo will look like and how blurry the background will be after playing with different lenses, different apertures and different distances from your object. If you own zoom lenses start with taking photos of a relatively close object while using your zoom lenses. You will find out that it is extremely easy to get a blurry background photo using this method even without setting the aperture. Once you feel comfortable with that setup start changing the aperture and also change to your normal 18mm-55mm or similar lenses.
Most cameras allow to manually change the aperture by putting the camera in “A” mode – while you are changing the aperture the camera will automatically set the shutter speed accordingly. Some cameras allow you to manually set both aperture and shutter speed.
In conclusion shooting dramatic blurry background photos is easy with some minimal understanding of depth of field and some experimenting.