Wednesday, April 25, 2007

Quick Tip #4: Take Control of Focus

I'll admit it...

I like to be in control.

Other than generally frustrating my wife (and causing some awkward moments with the TV remote), wanting to be in control means I tend to choose the manual option instead of the automatic option. I didn't get a car with an automatic transmission until we needed a mini-van. It took me five years to sign up for payroll deduction of my rent instead of sending in checks. The first few times I did my taxes I did them on paper instead of using a web site. (did I mention I was stubborn too?)

I want to be the boss when I take pictures. Then if they turn out bad, I only have myself to blame.

Modern cameras have auto film winding, auto exposure, auto white balance, auto focus, etc. I started out letting the camera auto-everything, but as time goes on, I'm taking control back bit by bit. The first bit of control I've taken back is focus -- I find my 350D does a great job of focusing on an object, but leaves a lot to be desired when it comes to choosing which object to focus on.

Think about it: given an object to focus on, it is an engineering problem to make the lens focus (Wikipedia has a good page about autofocus technology). Those camera companies are great at engineering. But, choosing what to focus on given a crowded scene, that is a hard artistic problem. Sometimes your kid will be in the front of the crowd, sometimes in the middle, sometimes at the back. The camera doesn't know which kid is yours (although, given time, I'm sure they'll engineer that in too -- Nikon already does face recognition).

Most DSLRs use a group of focus detectors built into the viewfinder to determine if and when focus has been reached. These detectors will focus optically using the scene in front of them (not to be confused by infrared focusing in point and shoot cameras). Cheaper cameras typically have three to five sensors (or sometimes just one) while more expensive models have nine or more. Either way, the camera will focus using the sensor which detects the closest object. There's also a distinction between the type of lines the focus sensor will work with (cheap sensors detect vertical lines, expensive cameras can detect both horizontal and vertical lines with the same sensor).

So, what if you are taking a close-up of someone's face? Instead of focusing on the eyes (where humans usually look first) the camera could focus on the nose or hat. Or, worse, if you try to take a picture through a fence or a dirty window, the camera might focus on the fence, or worse, get confused and keep switching back and forth, hunting for what it should focus on. Or, in the case of the picture that opened this entry, what if you are trying to shoot a small lizard in a deep crevice between rocks?

Luckily, modern DSLRs let you select which focus points to use (or you can choose all of them). So I keep my camera set to only the center sensor most of the time. That lets me do the old pre-focus and pan trick: point the focus center at what you want to be in focus, hold the shutter release half-way to make the camera autofocus on it, then reframe the scene how you want it and press the shutter. With practice, all of that can happen in a second or two. If you are shooting through a fence, you can either thread the needle through the fence or focus on something away from the fence (but at the same distance as your subject) and then point back to your subject to get the shot.

This is basic, basic stuff which most people probably already know. But since I've been practicing it (and I usually use the focus and pan method 90% of the time) I've had a lot less images that aren't in focus. Like 5%. So now, I can concentrate on getting the right look on someone's face or getting an interesting point of view.

What about that other 10% of the time when I use the group of sensors? That's usually when action is fast and I won't have time to get focus and reframe (such as sports, large groups of people, or kids on a playground). Actually, for fast action like sports, there are extra modes on my 350D which focus constantly (instead of once). I have yet to master those, though, but maybe I'll talk about them at a later date.

Oh, and the lizard pictured in this page? I found him at the cactus garden. At first, he was doing little lizard push-ups (I can't figure out if that was to intimidate me or to use parallax to figure out if I was still there). Either way, I got tons of pictures of him and got pretty close before I finally got too close trying to take macro shots. After that, he (and his mate) kept eyeballing me from between two large rocks. So I plunked my Sunpak 383 down at 1/16th power and took a few shots with the flash illuminating the inside of the rocks.

And yes, to get the photo I pre-focused on his eyes and then reframed the shot.

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