How Cameras Work

This week we’ll be talking about the basics of how a camera works. This is a bit of a crash course and I’m going to whip through it as quickly as possible. Sorry for the dry technical bits – there’s no good way around them. Hopefully in trade for the pain you’ll have a better idea of how your camera works.

Cameras are basically boxes that capture light. It really doesn’t matter if you’re using a 35mm film camera or a digital point-and-shoot, they all do the same thing. The image you end up with is a result of how much light you’ve let into your light-catching box. This is called an exposure. If you let too much light in, then you overexpose the image. If you let too little light in, you do the opposite – underexpose.

Most digital cameras are smart enough to figure out your exposure for you. But sometimes the camera guesses wrong, so it’s a worth understanding how a camera captures light so that you can take control when you’re not getting what you want.

If you’ve studied anatomy, you might remember the human eye has basic parts – the retina, the iris and the lens. The retina sits at the back of your eye and captures light. The iris controls how much light gets to the retina. And the lens let you focus on an object.

Cameras have the same basic parts, with different names. The retina becomes the image sensor, the iris is called the aperture, and the lens is called (wait for it…) the lens. We’re going to ignore the lens for now, and add in something a camera has that they eye doesn’t – the shutter, which is basically like a blink.

There’s one major difference between eyes and cameras. In a camera, you can change how sensitive the sensor is to light. This sensitivity is measured by ISO.

ISO

Once upon a time cameras recorded images onto film, and there were all sorts of film manufacturers. Each type of film had a different sensitivity to light, and were rated for this sensitivity by an ISO film rating like 100, 200, 400, 800. Higher numbers meant the film was more sensitive to light. The trade off was that the higher the speed the grainier the image.

We’ve moved from film to digital sensors, but we’ve kept the same ISO scale and the same trade off. As you set your sensor to be more sensitive (by selecting a higher ISO setting), you create more noise (grain) in your image.

Aperture

Aperture settings are probably the most confusing part of a camera. They have a weird numbering system called f-stops: 1, 1.4, 2, 2.8, 4, 5.6, etc. It also works in the opposite direction than you think it does. The higher the number, the less light is let through the lens.

For those of you wondering why, it’s because the the aperture setting is the bottom half of a fraction – 1/(your aperture setting) – written something like 1/2.8. This might make your eyes bleed and head explode. Relax, step away – all you need to remember is that the higher the number the less light get’s through to the sensor.

Shutter Speed

When you blink your eyes, the image you see goes black momentarily as the light gets cut off. Shutter speed works in the exact opposite direction – when you press your shutter button (the one you press to take the picture), the shutter blinks and momentarily lets the sensor see the image. Shutter speeds are measured in fractions of a second, like 1/30, 1/100, or 1/400. The higher the bottom number, the faster the shutter speed and the less light gets to the sensor.

There’s a trade off in this as well. If you go much below 1/100, you end up with a blurry picture. This get’s really bad if you’re shooting in a dark room. Here’s where the balancing act begins.

The Balancing Act

As you’re taking pictures, you’ll need to change these setting in order to get a proper exposure. If you’re in a dark room, you might need to up your ISO to make your camera sensitive enough to get a picture without blurring. If you’re outside on a bright day, you might need to close down your aperture (choose a higher f-stop) so that you let less light get to the sensor. Other times, you might be taking a picture of something moving really fast, so you choose a higher shutter speed to freeze the action.

Most of understanding how and when to use different settings comes from experience. Some cameras are really basic and don’t give you much control over these different settings. But it’s worth knowing what is happening inside your camera so that you know what you can and can’t control.