Controlling depth of field can create really powerful images. Have you ever wondered how you can do that yourself? Perhaps you want to take a portrait of someone and have the background blurred, or maybe you just want the main element of your picture to "pop". That's the topic of this article.
Let me first give you an example of what I'm talking about. In the below image, I wanted the focus to be on the loon, with the canoer and the shoreline in the background to be a little blurred.
In my last photography blog article, I mentioned the exposure triangle. In order to achieve the above results, the main element to consider is aperture.
What is aperture? It's essentially the size of the hole that lets light into your camera. Almost all camera lenses have the ability to change the aperture (except fixed aperture lenses, which generally have more specific uses).
The larger the "hole" that lets light into your camera, the shallower the depth of field. So in the picture of apertures above, the largest aperture is f/1.8, which would have the shallowest depth of field, and f/11 would have the deepest depth of field.
It is worth mentioning that as you increase an f-stop (the term used to describe how big the aperture is), you halve the amount of light you're letting through to your camera's sensor. So for example, when you change your f-stop from f/2.8 to f/4, you are now letting in half the amount of light. It's the exact same thing when you move from f/8 to f/11.
Also noteworthy is that f-stops are a mathematical relationship that that have to do with the surface area of the hole. You have to remember the numbers, they're not sequential. As an example - f/1 is not half as much light as f/2. The scale is:
1.4 / 2.8 / 4 / 5.6 / 8 / 11 / 16 / 22 / 32 / 64
So therefore, if you want to narrow the depth of field, you will want to use a smaller f-stop number (which means a larger aperture).
If you have an expensive lens/camera, you should be able to decrease your f-stop number fairly low. The picture above was taken using F/5.6, which isn't that low, but effective enough when combined with a zoom lens.
Now obviously as you increase f-stop numbers (decreasing the size of the aperture and therefore the amount of light you're letting through), you will need to adjust your camera using the other two components of the exposure triangle: shutter speed and ISO. Those are topics for another day.
How to practise: If you're comfortable using manual mode, playing around with all 3 elements of the exposure triangle. Otherwise, put your camera into Aperture Priority mode ("Av" on your dial if you're using a Canon). That setting allows you to control the Aperture Value (Av) manually, and the camera will automatically adjust ISO and shutter speed.
By Rick Sturch
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