Take Control of your Photos: Spin the Knobs Like a Pro!

You can control how light a picture is with shutter speed or f-stop, but they both can cause blur. The secret is predicting the blur so you can avoid it, or use it to your advantage.

Good photographs don't happen without good light. Part of this is the quality of the light, such as warm vs. cold, but also it's the balance of light in a photo and amount of light. The simplest to get a grip on, amount of light, can be illustrated with a couple of extreme examples: a dark room and a sunny snowfield. When you take a picture (without a flash) inside a room, the picture is usually too dark. When you take a picture on a sunny day in the middle of a snowfield, the picture is usually too light. In order to take photos with the right amount of light, you need to spin the knobs on your camera to correspond to the natural lighting conditions (I'll talk about augmenting the natural light with flash in a later post).

A camera is basically a box with a hole in it that lets light in. The light either exposes film or catalyzes some digital voodoo to produce a picture, but the amount of light that gets through the hole makes the picture too bright, too dark, or just right. Photos that are too light are easy to darken with a faster shutter speed or a smaller aperture setting. Lightening a dark photo is where the problems begin. There are two ways to control the amount of light getting through the hole: shutter speed (how long you let light through the hole), and aperture setting (how big the hole is). The rub is that they both have blurriness as a potential side effect.

If you let light through the hole for a long time, the picture will be lighter
The first way to control the amount of light in a picture is to leave the shutter open longer thereby letting in more light. But slow shutter speeds will cause blurriness because while the shutter is open, things will move. The camera will see this movement and capture it as a blur. This can be a good thing or a bad thing. It can be a neat effect when shooting a waterfall, for example, or on an ultra-long exposure of the night sky where you capture the circular movement of stars.Both of those examples assume that only one thing is moving: the thing you want to move. But that’s not what really happens. The camera is more often what moves because it's very hard to hold a camera steady for more than 1/60th of a second. That’s why you need to use a tripod with slow shutter speeds; to control the blur.

If you make the hole bigger, more light can get in faster
The second way to control the amount of light in a picture is to make the size of the hole that lets light into the camera bigger. This hole is called the aperture, and its size is measured in f-stops. To make things seem harder than they really are, f-stops are the inverse of the aperture size, or 1/aperture. An aperture opening of f2.5 is bigger than f16 (even though the number is smaller), so all other things being equal, the photo will be lighter on f2.5.

Again, spinning the knobs down to a lower f-stop can add blur, which can be a good thing or a bad thing, depending on how you use it. F-stop determines how wide a range the camera can focus on, or it’s depth of field. Very small f-stops have very small depths of field. The camera can only focus on a very limited range in front of and behind the subject you’re focusing on. The foreground and background will appear blurry. This can be an interesting effect, such as if you’re trying to highlight an object in a busy scene (a person in a crowd), but it needs to be intentional, or you’ll be disappointed.

Combine shutter speed and f-stop to get the shot you want
Mixing these two settings in various combinations can allow you a ton of flexibility in controlling the look of your photos. If you know that you want to keep the shutter open for a long time, to make the waterfall look really cool, you’ll have to use a tripod to steady the camera, but you’ll also have to close down the aperture so that the photo isn’t blown out (too bright). This will put most everything in the viewfinder in focus.

Automatic camera settings are typically pre-engineered to account for depth of field, fast movement, or low light; and sometimes, that's the easiest way to go. But now that you understand how to control this stuff yourself, you're not handicapped by the pre-sets.

There's another way to lighten a dark setting
Now that we’ve talked about the two ways to lighten a photo, there’s one more way: film speed, measured in ISO rating (formerly known as ASA). ISO is a measure of how sensitive the film is to light. Typical daylight conditions call for an ISO of around 100 or 125. Night photography needs a film speed of around 1000. Digital cameras don’t use film, but they have ISO settings, so you can boost up your ISO for dark conditions, but the side effect is that the photo will be grainier than it will be at a lower setting. Practically, this means you have to print the photo smaller, or that you can’t blow it up as much. But at least you can print it right? When shooting photos at trade shown inside a convention center, I typically boost the ISO to around 400 so that I don’t have to use a flash (which is annoying to many people).

The other way to boost light is to provide more light either with a flash, more ambient light, or both. I’ll cover that next.