Photography basics - Exposure

Many friends who are beginning to learn photography are asking me “I want to go beyond the basics. What should I know?” I decided to write a series of tutorials on the basics of photography to aid those who want to go beyond point-and-shoot, those who want to be in control of their cameras.

If you don’t know what the exposure or aperture are, this little tutorial is for you, so read on. I’ve done my best to avoid overcomplicated technical details and give lots of analogies and examples instead, so enjoy.

Follow up:

Understanding exposure

The single most important thing to learn about when making a photo is exposure. You’ll never go beyond point-and-shoot without understanding how this works. Any gorgeous scene can and will be ruined by bad exposure.

Lighting the model while keeping
the details in the sky was tricky,
because the sun was behind the
model (backlight situation)

How do we capture the light in the scene in a photo? Whether we talk about film or digital, the principle is the same: we’re letting a piece of light-sensitive material to gather light from the scene.

How much light do we need to capture? Here’s the tricky part. Each scene has a certain amount of illumination that can be measured objectively using a light meter. The typical unit of measure for luminance is called “lux” but most light meters are set up to display results in photographic terms (more on that later).

Most likely however, you won’t have a light meter, so you can’t rely on them. All photo cameras have their own light meters, except they can’t measure the actual light levels from the light source(s), but the light that enters the camera, which is the reflected light by the scene onjects. Why is this important? It’s because the camera has to “guess”. The camera tries to find a good average of the light intensities - here’s how it works:

This is the original image

The camera takes readings of light intensities across different areas of the image. The number of segment and pattern varies from model to model.

The readings are averaged based on different algorithms (“evaluative”, “3D matrix”, “center-weight”, etc.) and the exposure is adjusted to obtain a medium gray.

This method works most of the time - but sometimes it misses. Do you have your camera nearby? Take a picture of a white sheet of paper. - just the white paper, without anything on it. Download the picture and look at it on the screen. I’m willing to bet it came out gray-ish. Take another shot of a black T-shirt. Have a look at it, it’ll be gray or dark gray. Why?

White or dark backgrounds
can fool the camera meter

The camera tries to average everything to gray. If a scene has bright areas and dark areas, the camera can determine a proper average and from that, it can determine the exposure. But, if you’re shooting tricky scenes, it’ll fail (even a sunset or a portrait against a white wall can be considered tricky, so don’t think you won’t encounter such cases).

Moreover, digital cameras (and film too although to a lesser extent) cannot capture the full dynamic range of light and shadow that our eyes can. If you’re indoors and it’s day outside, take a picture of the room pointing out to the windows. Either you’ll get the view outside looking nicely and the room totally dark (underexposed), or the room will look OK (exposed correctly) while the view outside will be completely washed out (overexposed). As a photographer, you’ll have to take care of these high-contrast situations and avoid them or, even better, use them to your advantage.

Hopefully, by now you understand what exposure is and why it’s important to get it right. Next, it’s how do we get it.

Let’s move on to the next page:

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