How many of us have taken a picture like this? Your attention should be drawn to your favourite feline, but the background is so distracting it loses something.
What we’re really looking for is this.
This is a beautiful shot! You’d never know it, but that’s the Detroit skyline in the background. It’s so blurry you can’t tell and it lends a real artistic flair to the photo.
So how do we go about achieving this photographic miracle? We use the magic of depth-of-field control. Every lens in every camera focuses at one particular distance depending on where you turn the focusing ring. This puts the main subject in focus but the foreground (closer objects) and the background (objects further away) may or may not be in focus. In order to get the background in or out of focus we have to adjust the aperture of the lens.
When a lens is set to a very large opening like f1.8 it will cause the background to be completely out of focus. Only the main subject at the focus point is in focus.
As you move to smaller and smaller apertures, the background will come in to focus.
It’s really that simple! Here’s another example.
In the picture at the top you can see that the ball in the foreground and the ball in the background are out of focus because of the large, open aperture. In the bottom picture you can see that both the foreground and background balls are in focus along with the ball in the middle. In both pictures the lens was focused
on the middle ball. The magic of depth of field control allows us to selectively include a deeper (or shallower) field of focus, also known as “depth of field”.
The other way to control depth of field is to use different focal length lenses. A telephoto lens makes everything bigger in your picture, including any discrepancy in focus. So if you are focused on a bird that’s 50 feet away and the tree behind is 55 feet away then the tree is in the focus error zone and will be out of focus since that 5 feet of error has also been made “bigger” by the telephoto lens. On the other side of the equation, a wide angle lens makes everything smaller so more stuff fits into the frame. The focus error zone also becomes less significant as well so the tree in the background appears to be more in focus.
The picture on the left was shot with a telephoto lens and you can see that the background is somewhat blurry. The picture on the right was shot with a wide angle lens and the background is relatively sharp. The two lenses lend a different look to other aspects of the pictures as well but we’re just discussing depth of field at the moment.
Any questions? Feel free to comment! Take a moment and post some of your best shots to our Flickr Photo of the Month pool! https://www.flickr.com/groups/2767948@N25/