Getting Into Focus

So now you've got your spiffy new camera and you're just itching to start shooting. First off, I say go for it. Don't wait until you've had a zillion hours of instruction before you start shooting; nothing teaches you about how to use your camera better than just using it, with the single caveat that you need to pay attention to what you're doing. Digital cameras take making rookie mistakes from being painful and expensive (if you had to shell out good money to develop really bad photos) to easily deleted learning opportunities, but only if you learn something from them. Otherwise, you'll spend your life shooting nothing but junk, and and you don't want that, do you?

So the basic thing to know is how to focus. Well, that's easy, right? First of all, most digital cameras have electronic autofocus, which takes 90% of the guesswork out of simple photography, but I would warn you that autofocus isn't perfect. You're depending on a circuit board to read your mind and figure out what your subject is, and while the algorithms the engineers have designed into modern cameras are very good at guessing (some sense when a humanoid shape is in frame and assumes that's your first priority for focus, for example), they are not telepathic and can't guess what every photographer intends to capture every time. And what if you intend for everything to be slightly out of focus because you're trying to be artsy (what they call "soft focus" in the biz)? Your camera isn't going to understand that, so you're going to have to take manual control of focus to get what you want.

Also, even if you intend for the image to be tack sharp, your camera's autofocus is only as good as the guy who calibrated it at the factory. A number of digital cameras have the ability to fine-tune the autofocus, and after a bit of fiddling around with the controls, you can dial it in so that the autofocus is tack-sharp every time, as long as you make sure it's focusing on what you want in focus.

I know what you're thinking. "I'm not trying to make great art; I'm just taking vacation photos and the occasional picture of flowers in my garden, so shouldn't I just try to have everything in focus all the time?" Well, no - sometimes, it makes a photo stronger if your subject is in focus and everything in the background is artfully blurred - if you have to have other stuff in the background or foreground, in other words, it can help to make your chosen subject stand out if it's the only thing in focus. And sometimes your subject itself is viewed at an oblique angle and extends into the background, so you need more than just the closest portion to be in focus. So now we're not only talking about simply focusing on your subject, but also about depth of field.

Let's take a break for a moment and think about basic optics. The reason were able to see the world around us is because of light reflecting off of objects. Light coming in from a source (let's say, the sun) hits objects and bounces off in all directions.

However, you are only going to experience the light that bounces off the object at such an angle that the reflected light reaches your eye.

Your eye works much like a camera does, only instead of moving a lens back and forth, the lens in your eye flexes in response to muscle movement, which changes the focal distance and allows the image to focus on the rods and cones in the back of your eye.

So what? Well, let's take a real world example of this. Meet Sally.

Sally has graciously agreed to model for you for the afternoon. If we trace a beam of light from source to camera, it bounces off of Sally, passes through the lens of your camera (getting turned upside down in the process, incidentally, but no matter), through the aperture and then hitting the sensor or film inside the camera and getting captured as an image.

When you focus only on Sally, and there isn't anything else in frame, it's okay to have a shallow depth of field (that is, things in the foreground and background can be blurry, and she's the only thing in focus) because she's all you care about. Now let's say halfway through your modelling session, Sally's dog Rex wanders in. Because he's at a different distance from the camera, with a shallow depth of field, he's going to be out of focus because the light bouncing off of him is going to pass through the lens and create an image inside the camera that would be perfectly in focus if the sensor or film were just a little bit closer, but since it isn't, he's going to be blurry.

Here's the tricky bit. You can change your depth of field by varying the aperture. If the aperture is wide open like I'm showing here, there are essentially lots of different images of Rex and Sally that make it through, based on the angles of all the light bouncing off of them and making it through the lens. If, however, you close down the iris so the aperture is very small, it limits the angle that light can travel and still make it past the iris. In other words, only those photons that are at an angle to be in focus will be captured by the sensor or the film, like so:

Don't believe me? I just ran outside and took some pictures of a Dutch iris in my garden as an example. Here is one I took with my Canon EOS 5D Mark II, through a EF28-135mm zoom lens with polarizing filter at f/4.5 (wide open), ISO 400 at 1/1000th of a second exposure.

Note that the sage and lavender plants in the background are blurry. Depending on the kind of shot you're going for, you might even want the background blurrier, and would have to either push the depth of field even more shallow if possible or blur it later during the editing process (which might be preferrable, because shooting a three-dimensional object with a really shallow depth of field means that part of your subject might also turn out blurry, since only one part of it will fall into the focused portion of the field.)

If I close the aperture down to f/29, here's what I get:

Now more of the background is in better focus. Please remember, however, that now that I've restricted the light that can come in through the iris, in order to properly expose the picture, I'm going to have to fiddle with the shutter speed to allow enough light to hit the sensor (in this case, I had to slow it down to 1/25th of a second)

Your assignment: play around with depth of field and see where it takes you. I know, you're not a professional photographer, but I'm sure you've got vacation photos where everything was in focus and the picture of your family in the crowd of people in front of the Epcot sphere was kind of like a "Where's Waldo" puzzle; since everything was in focus, your family didn't stand out from all the OTHER sunburnt tourists wearing Mickey Mouse ears. So snap some candid photos of your family when you get a moment and play around using different aperture settings to see what happens (if your camera is capable of manually adjusting such things, obviously). You may be surprised at how much better this single change may make your vacation photos, and for the hobbyist or budding professional photographer, it's a skill that will become absolutely essential in your toolbox of tricks to get great photos. Have fun!