Photography tip • 29 March 2008 • The SnowBlog

Photography tip


Now I'm hardly a big expert on photography, but because we're publishers we do a lot with images. And there are one or two simple things I've picked up that are useful enough that it might be worth me passing them along. This is a tip about how to take photographs with fuzzy backgrounds. Now why would you want to do that? The answer is that it looks good. Movies do it the whole time. The actors' faces are in focus but the background isn't. The result: you look at the actors and think the background looks arty. Or think of it like this: your first decision is which direction to point the camera in. Your second decision is what to focus it on. And that second decision is taken away from you if everything is in focus. So there's a tiny bit of theory to this, but I'll try to make it painless. 

There are four bits to a camera. 1) The lens, like the lens in your eye, focuses the light. 2) The aperture, like your iris or your eyelids, cuts down the light by covering part of the lens. 
3) Then there's a shutter. It can open for a short time to let a little light in or longer to let more in (in the olden days, they just used to take the lens cap off for a moment.)
4) And lastly there's the film or sensor (I'm assuming most people use digital cameras these days) which captures the light. 

Even though understanding lenses is tricky, most of us understand the idea that you fiddle with the lens until the thing you're photographing looks sharp. But how do we control whether the background is in focus too? 

The answer is to use the aperture. It not only cuts out light; it has an effect on focus. If you close up the aperture so that only the centre of the lens is uncovered like this:
that not only cuts down the light coming into the camera, it also makes all the light go through the middle part of the lens which is the bit best able to focus lots of different things at once. 

If you open the aperture out so that the lens is hardly covered at all, like this:
then not only do you let more light in, but light will go through the outer part of the lens as well as the centre. The result is that whatever you focus on still looks sharp, but everything else in the shot will be fuzzier.

Here's an example of what that looks like (stolen from this site). Here's a shot with the aperture closed up. This is referred to as a wide 'depth of field' (i.e. lots of the shot is in focus):
And here's a shot of the same scene with the aperture opened up. This is a narrow 'depth of field' (i.e. only a few things are in focus):
Now, maybe you like the first shot better, in which case set your camera to automatic and it's probably what you'll get. But if you want pictures more like the second, you need to make sure your camera has its aperture open as wide as possible.

Telling an automatic camera what aperture you want usually involves finding a little dial like the one in the picture and setting it to 'A' for 'aperture priority'.
In 'aperture priority' mode, you choose the aperture and your camera tries to make sure there's enough light for your shot by adjusting how long the shutter stays open for. Look in your camera's manual to see how you set the aperture, but you want to make the setting a very small number. You could think of this number as controlling how much of the scene is in focus: if it's a low number, only a few things will be in focus, if it's a large number, then more of the scene will be in focus. Dial the number down as low as you can go and still take a photo. 

(To repeat: a small number for aperture means small depth of field because the aperture is open, large number means large depth of field because the aperture is closed. What's slightly confusing is that the number goes down the more you open up the aperture, but just think of that number as activating the aperture, increasing how much it's used and hopefully it makes sense then that you increase the number to close the aperture. And you turn the number way down to effectively turn off the aperture as though it wasn't even there.)

The final point to mention is that since arty, shallow-depth-of-field photos involve having the aperture wide open, there's a lot of light streaming into the camera. The camera cuts this down, if it's too much, by snapping the shutter more quickly, but on a bright day there might still be too much light. That's where filters come in. You put a polaroid filter (made from the same stuff as polaroid sunglasses) on the camera and now you can open the aperture up even in bright sunshine. And with any luck, there'll be some of that on the way soon. 


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