We’ve all heard people say, as they look through their (or our) photos, “Oh, that one is not properly exposed,” or “This one is overexposed,” and “That one is underexposed,” and sometimes when it looks really good, “Great exposure,” but have perhaps wondered what is meant by these terms, and, more importantly, how to expose photos correctly.

Or perhaps you didn’t wonder and just let the comments slide by. Perhaps you have looked at some of your photos and scratched your head with a vague uneasiness that there might be something you could have done to make them look more like the ones you see in National Geographic or in those emails someone sends around every now and then with “Best photos of 2009” or some such.

So, what is exposure? What is one exposing to what? And how do you do it right?

In these days of point-and-shoot digital cameras and auto-toning in our favorite photo processing software, one can get the idea that these basics of photography can be dispensed with, since it will all be taken care of by the latest supercamera. But still, those photos that don’t quite look right…surely something can be done to make them look better.

The answer of course is resoundingly YES. Something can be done to make your photos look brighter, more colorful, more sparkling, richer, less washed out or less dingy…in short, more professional. But you have to understand the basics. Nothing in this world of sophisticated digital equipment and all-singing-all-dancing software has supplanted a knowledge of the basics, of tools and techniques. The results, if you are even a little serious about your photography, will be well worth the time taken to understand the whys and wherefores and the how-tos.

It is almost a cliché for professional photographers, when someone looks at one of their beautiful photos, to hear the question, “What equipment do you use? It must be a very special camera!” They answer politely, but under their breath, if you listen closely, they are saying, “It’s not the camera, my friend. Do you know how many hours of study, learning, theory and practice it took to get this good?” And it’s the truth. You could give them a cheap, point-and-shoot camera and they’ll still take a better shot than the uninformed can with their super DSLR.

So, let’s roll our sleeves up on the subject of EXPOSURE. If you know all this already, you can read it as a refresher. If you sort of understand it but it’s a bit hazy, then read carefully and don’t miss anything. As a photographer you should have a good grasp of these principles. This is entry level information. But surprisingly enough, many photographers never really grasp these points and just muddle through, wondering why their results were not what they expected. So it’s worth checking to make sure you really do understand these points.

What is EXPOSURE?

A photograph is made by focusing some rays of light through a lens onto a light sensitive material of some sort where it is captured. In the case of film, it is captured through a chemical process. In digital photography, the light falls on a sensor and is captured and recorded electronically. In either case, the image you see in front of you is projected onto light sensitive material where it is recorded. It is the film or sensor which is exposed to light coming in through the lens. EXPOSURE refers to the light being allowed to fall on the light sensitive film or sensor – how much light and for how long.

Correct exposure means that the right amount of light has been allowed to fall on the film or sensor in order to produce a photo that looks the way you want it to – as dark or as light as you want it to look.

Overexposure means that the film or sensor has been exposed to too much light. It looks washed out, the colors pale and insipid, the detail in the lightest areas lost completely as they have gone white. That bronzed, healthy face of the guy in the picture looks pallid and a bit ill, the eyes pale and insipid.

Underexposure means that not enough light has been allowed to reach the film or sensor. The photo is too dark, the shadowy areas have gone black and the detail has been lost. In extreme cases the fair and lovely face of the girl has turned into a shadowy, dark blob in which you can hardly make out her beautiful eyes, let alone tell what color they are. Look at the photos below.

Of course there are degrees of these things. There is the disappointment when that beautiful sunset where the sky looked so dramatic seems to have lost its effect in your photo. Or the delicate colors of the dew covered rose bloom seem to have gone a bit muddy and dark when you print your shot of it.

Take heart! When you understand exposure, all these disappointments can be turned into the joys of success. It took me ages to figure this out, so don’t be discouraged if it doesn’t immediately come to you. If you’re shooting digital, and most photographers are these days, then the lighter you want the photo to look, the more light you have to let into the camera. If the photo is too dark, you have to give it more light. If it’s too light, you have to give it less. If you’re shooting film it gets complicated because the above is true for slide film but the opposite is true if you’re shooting print film. If your print is too dark, you underexposed the negative. If the print is too light then the negative is overexposed. If you are shooting digital, don’t even worry about trying to figure this out. Just give thanks that you are shooting digital and remember: too dark? Underexposed. Too light? Overexposed. It is MUCH easier. We’ll get into the How of getting it right as we go along.

Correct Exposure

Generally speaking a correct exposure is one in which the highlights (the lightest parts of the photo such as the sun reflected on the water, the whites of the eyes) are bright without losing fine detail, there is a full range of tones all the way through to the deepest black, yet you can still see important detail in the dark areas. But in the end, correct exposure means that the tones in the photo (light, middle, dark and everything in between) looks just the way you want it to. If you can get the picture to look the way you want it to in terms of dark and light tones, then you have mastered exposure.

And the best news perhaps, is that there are only three factors which affect correct or incorrect exposure and you can control them all, even on your point-and-shoot camera, let alone on your fancy DSLR.

And these days, with digital cameras and photo editing software, you have more control than ever and any old-time photographer who struggled in the darkroom, his hands stained with chemicals, would be green with envy at the tools you have to create perfect photos. This is a great time for photographers.

The Magic Triangle of Exposure

There are three ways to control exposure when shooting. I say “when shooting” because there are also many ways to control it after the fact, on your computer if you are shooting digital, or in the developing and printing if you are shooting film. But remember this: no matter how good your photo editing software or how skilled you are with it, or how professional the lab you send your film to, you should go for the best exposure you can get in the camera and not rely on processing it afterwards. The better the raw material (original photo) the better your final photo is going to be. More of that later or in a separate article.

ISO Setting

The first control is the ISO Setting. ISO stands for International Standards Organization. In photography it is a number which indicates how sensitive the film or the sensor is to a given amount of light. With film this is referred to as “film speed.” You can buy film which is rated at ISO 50. It is called “slow” film because it is not very sensitive to light. You can buy ISO 1600 film which is very sensitive (“fast”) and is useful for low light situations where there is action (basketball games come to mind). You can set your digital camera to ISO 100 (less with some cameras) or 1600 (or a lot more with some cameras) to change the sensitivity of the sensor. The higher the ISO setting or rating, the more sensitive the film or sensor is to light falling on it.

Aperture

The second point of control is Aperture (which just means an opening). This is the hole in the camera that the light comes in through. Sitting inside the lens usually, it is controlled by a diaphragm composed of a number of leaves, usually metal, that can be adjusted to form a wider or narrower hole. The settings are called “f stops” and come in numbers such as f1.4, f1.8, f2.0, f2.8, f3.5, f4.0, f5.6, f8 and on up to f32, f64. The higher the number, the narrower the hole. How the numbers are derived is not important. Obviously the wider the aperture, the more light it will let through in a given period of time. This can be controlled.

Shutter Speed

The third control is the Shutter Speed. This is a mechanism which controls the amount of time the light is allowed to come through the aperture to hit the film or sensor. When you are not taking a photo, the shutter is shut. When you press the exposure button on the camera, it opens the shutter for a predetermined, precise period of time and then shuts it again. This can be a second or several seconds but more usually is a fraction of a second, such as 1/30^th or 1/125^th or 1/1000^th of a second – a very short period. Back in the old days when the glass plates they used to record the picture on were not very sensitive to light, the “shutter” used to consist of a lens cover which the photographer would manually remove while he timed the exposure on a watch or stopwatch and would then replace at the end of a given number of seconds or even minutes. No wonder the models used to use neck braces for their portraits. And no wonder the sitter sometimes looks a little stiff in those old sepia prints or plates from the early days of photography.

The Triangle

These three factors act together and there is almost always some kind of compromise between them where you have to emphasize one at the expense of one or both of the other points. This will all be explained in this and further articles. But they work together. For example, a faster shutter speed requires a wider aperture if you want to achieve the same exposure. You can see why. If you’re going to allow the light in for a shorter period of time, then you have to allow more light in per unit of time to get the same exposure. If you want to use a narrower aperture (and there are times that you do, as we will see) then you will have to use a slower shutter speed – the smaller amount of light per unit of time requires longer to have the same effect on the film or sensor. And when there just isn’t enough light to get a decent exposure and still have a sharp photo, you can increase the ISO setting or use a faster (more sensitive) film.

Those are the three points of control you have when taking a photo to make sure that it is exposed correctly. And while a fully automatic camera controls these three settings without even asking you, it doesn’t always get it right and cannot replace your understanding of the three settings and your ability to control them to various degrees which are required if you want to get great photos all the time.

There is a lot more to know about these three settings. We will cover ISO Setting here and then go into detail about Aperture and Shutter in separate articles. By the time you have studied these three articles you will have a good, working understanding of the basics of exposure and be much better able to get it right.

ISO Setting

The basic principle is that the higher the ISO setting on your camera or the higher the ISO rating of your film, the more sensitive it is to light. It is a straight numerical progression: ISO 100 is twice as sensitive as ISO 50. ISO 200 is twice as sensitive ISO 100, ISO 400 twice as sensitive as 200, and so on.

So, you say, I’ll just set my ISO up here at 3200 and I can take photos in any light condition no matter how dim or bright. Or, well, I’ll just buy 400 or 800 ISO film and just use that and I’ll be all set. Unfortunately the much touted nonexistence of free lunches applies here too and, as with many things in life, there is a trade-off. The higher you set the ISO, or the faster the film you use, the grainier and noisier your photo gets, the less saturated the colors, the lower the definition. In other words, the sacrifice for being able to take photos in lower light is quality. It’s true of film and of digital photography. You lose quality. Even going from ISO 50 to ISO 100 (twice as sensitive) you will notice a difference when you really look. The manufacturers of film and camera sensors are constantly struggling to reduce the loss of quality that comes with higher ISO ratings or settings. In a perfect world the photo taken at ISO 1600 would be just as crisp, brightly colored, sharp and clean as the one taken at ISO 50. In the real world, the ISO 1600 one is going to be to some degree fuzzy, grainy, spotty, discolored.

The following photos of the same subject taken on a digital camera, one at ISO 50 and the other at ISO 6000 will show you what happens. There is no other difference between the photos.

ISO 50

ISO 6000

On brief inspection, especially at that size, they look fairly similar. What’s the fuss? you ask.

Well, let’s blow them up a bit. The next two photos are an enlargement of one of the lilies. This is at 100%.

ISO 50

ISO 6000

If you printed them off you would see it even more clearly. And let’s blow it up even more so it’s really clear. Let’s look at the same photo at 300% enlargement. Again, the ISO 50 photo is on the left and the ISO 6000 is on the right.

ISO 50

ISO 6000

So, in general, unless you are looking for a grainy effect, you should set your ISO as low as your camera will go and light permits: in normal outdoor shooting in medium to bright conditions you should be able to set your ISO to 50 or 100 (different cameras have different minimum ISO settings). If you’re shooting film you should stick to ISO 50 or 100 film if you know that you’re going to be shooting under these conditions.

When you have read the next two articles on Aperture and Shutter Speed and put all the information together, you will be able to judge better where to set your ISO (or what speed film to use) for given light conditions and what shutter speed and aperture setting to use to get the right exposure.

Remember, the only reason to know all of this is so that you can get your final photo to come out the way you see it and the way you imagine it should look.

These then, are the basic factors of exposure.

Next in this series will be Aperture. It might just as well be Shutter Speed. They are of equal importance even though they are very different in nature. It doesn’t matter which you read next as long as you read them both.

David © Phillips is a professional writer and photographer living in Seattle, WA. You can find out more about him and his work at www.dcpcom.com.