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Today we’re going to explore a fairly easy photography technique known as depth of field. Well, it’s easy once you know how it works. Like anything else, it probably seems like arcane magickery if you have no idea what I’m talking about.
Hopefully by the end of this brief post, it’ll be arcane magickery no longer.
What is Depth of Field?
I figured there’s no point trying to explain how to achieve depth of field if I don’t tell you what it is first. Clue: it has nothing to do with grass, unless you’re taking a picture of an actual field.
Depth of field is just a fancy term to describe how much of your picture is going to be in focus when taking a shot. The “field” in this case refers to the field of view (what’s in your picture) and the “depth” refers to how much of that field of view is in focus.
Let’s say you are taking a picture of a cow, in a field.
Maybe you want the cow to be in focus, nice and sharp, but you don’t want the viewer to be distracted by things like the trees in the background, or the playful dandelions in the foreground.
In this case you’d choose to use a shallow depth of field, making the cow – and everything else on the same plane as the cow – in focus, with the objects in front of and behind the cow pleasingly blurred out.
Got it? No?
Ok, here are a couple of pictures of a beer bottle to explain. Because everything is easier with beer.
In the shot above, on the left we have a picture of a beer bottle with a fairly normal depth of field. On the right, there’s a beer bottle with what we can refer to as a shallow depth of field.
On the right, only the beer bottle is in focus. Everything else is cunningly blurred away, meaning the viewer isn’t distracted by leaves and clouds and roof detail and is basically forced to look at the subject of the shot.
So now we know what depth of field is, let’s talk about why we’d want to use this technique.
Why Use Depth of Field?
As alluded to above, depth of field is a way to control the parts of your image that you want to emphasise.
Shallow depth of field works particularly well for portrait and food photography. It allows you to direct your viewer’s attention to that carefully placed lettuce leaf, for example, whilst cunningly hiding the awful shirt of the waiter in the background.
On the flip side, if you’re doing landscape photography, you’re going to want as much in focus as possible. In this case you’ll be using a deep depth of field, allowing everything from the cowpat in front of you to the mountains in yonder distance to appear clean and sharp in your final masterpiece.
How to Do It (With Technical Description)
Now we’re going to get a bit technical. Not too technical though – if you want too technical, feel free to read my 3,500 word essay on SLR’s and photography. I’m sure one day someone will read it right through to the end. Now, for the technical sentence:
Depth of field is controlled by adjusting the aperture of your camera.
Still there? Awesome. We’re totally getting to the good stuff.
The aperture of your camera is the hole in the lens that lets the light through. The bigger the hole, the more light that comes through. The smaller the hole, the less light that comes through.
This could then lead us on into a complicated discussion about shutter speeds and ISO numbers, but that is a tale for another day. Let’s just focus on aperture for now.
For some reason, known only to Google and photography students, the size of an aperture is called an f-stop. It’s a number that varies from fairly small, like f/1.2, through to somewhat bigger, like f/22.
Hilariously, the smaller the number, the bigger the hole. Sometimes I think people come up with these ideas just to make them difficult to explain.
And now on to the crux of the matter.
Aperture directly controls depth of field. That shot of the beer bottle above? The right one was shot at a wide-open aperture of f/1.8 – a huge hole in the lens, resulting in a very shallow depth of field.
The shot on the left was a tiny aperture of f/22, with far less light coming in, resulting in a deep depth of field.
So far so good! Let’s talk about how to apply that to your camera. But first, another picture of some beer. Mmmm. Beer.
How to Do It (Skipping the Technical Bit)
You’re going to need to be shooting with a camera that offers you some kind of manual control. If so, it should have an Aperture priority mode, possibly labelled as A or Av on your camera mode dial.
This will let you set the aperture, and the camera will deal with everything else for you. If you want to take a picture with everything blurred as much as possible, set the aperture to as small a number as possible.
If you want as much as possible to be in focus, then set the aperture as high as it can go*.
And that’s pretty much it!
If you’ve got anything to add, got further questions, or just want clarification, feel free to let me know in the comments below!
*Setting the aperture higher means less light gets into the camera. To compensate, the camera will set your shutter speed to be lower, which in turn means your camera will be more sensitive to wobbles.
To avoid blurry shots, keep an eye on what your camera is doing to the shutter speed as you adjust the aperture, and don’t shoot at shutter speeds less than 1/60th of a second (or use a tripod.)