Note: Completing this lesson requires a camera capable of manually setting exposure.

What is the right exposure? Not to make this complicated, but exposure is a choice you have to make. The exposure you choose determines how the image looks. But, we’ll start with a basic understanding and work up from there.

Exposure consists of four factors:

1. how much light is in front of you – which can be changed by adding lights or flash,
2. how sensitive the film is to light – called ISO (remember, I use the word “film” to refer to whatever medium used for capturing the image, whether it is the Digital Camera’s sensor or actually film,)
3. the amount of light going through a lens – called the aperture,
4. how long the film is exposed – called the shutter speed.

For a little more about how this works see the Camera Basics Page.

For the moment, we’ll set an average exposure on an average scene.

If you’re camera does not have a built in meter – its really old. But, that’s okay. You’ll just have to buy a hand held meter. If you have an SLR or advanced point and shoot digital camera, spend some time with the manual to find out how to bring up the “Histogram” which graphically shows the amount of light in an exposure.

First exercise – set your ISO to 100, set your camera to ƒ16 and the shutter to 1/125th of a second. (Some digital cameras are limited to ISO 200 – which means you have to cut your exposure by one stop, i.e. use 1/250th instead of 1/125th of a second) With this setting, take your camera out during a sunny day, put the sun behind you and shoot anything – you’ll have a well exposed image. This is called the “Sunny 16″ rule.

To make life interesting, and your photography more creative, you can change the setting and still have the same exposure. These are equivalent exposures: Try going to ƒ11 at 1/250th of a second. Push it a little further at ƒ8 at 1/500th of a second. These are all the same exposure because the same total amount of light is hitting the film.

Of course, you’re not always going to shoot with the sun behind you on a sunny day. For other situations you need to be able to find out your exposure with a meter. This can be in your camera or hand held.

Looking at any scene, your meter will give you a suggestion as to what exposure to use. Most of the time this is fairly accurate.

Using your meter, take a reading off of something with mixed tones in shade on a sunny day – you’ll find the exposure is two or three stops slower than the “Sunny 16.”

Second exercise

One of the best things to do for more accurate exposure is to meter the light hitting the specific subject you’re shooting. Find a place where there is a small patch of light such as a break in a wall, light coming directly through a window, etc. Take a picture from far enough back you get lots of the shadow area. You’ll probably find the patch of light is way too bright in the picture. Walk right up to the patch of light and see what the meter suggests you use there. Then, go back to where you’re taking the picture from – and with the camera in manual – set the exposure to what was suggested.

You can also use your hand to help determine exposure in a variety of situations. First – on a sunny day, do the f16 rule, setting the camera to f16 at 1/125 of a second. Hold your hand in the sunlight and meter it. You’ll probably notice the meter says you should change the exposure. Note how much the meter says your hand is off from the f16 rule and keep that in mind. Lets say the meter said you should expose your hand at f22. That is one stop darker than what is actually needed. Now walk into the shade and meter off your hand again. If it says f11, you know that is one stop too dark, so set your camera to f8.

Knowing what your hand is for exposure can help you set exposure in most situations – just make sure your hand is in the same kind of light as the subject you’re shooting.

A little more accurate way to do exposures is to buy an “18 per cent grey card.” Most camera stores and photo departments should have these. To use it, just put it beside the subject you’re shooting, and meter off of it. If you’re further away than is practical to walk up to the subject – set the card in the same kind of light as the subject and again meter off the card.

Third exercise – either with an 18 per cent grey card, or using your hand as described above, meter something in dark shade and find out the exposure there.

A final note – A meter is very handy for getting your exposure, but it does have a limitation. As said earlier, the meter thinks the world is 18 per cent grey. Most of the world is kind of like 18 per cent grey, but not all of it.

Look at what you’re shooting. If its black (or very dark), your meter will try to make it grey – and make the exposure too light. Conversely, if you’re subject is white, the meter will try to make it darker – or 18 per cent grey.

There are two more lessons on high key and low key photos which will help you handle more extreme situations.

Note: Be aware that some digital cameras have exposure compensation built in to prevent overexposure. If exposure is too bright the highlights could be “blown out” and detail lost in the brightest parts of the image. By artificially “darkening” the image, the camera makers try to make sure the exposures aren’t too bright. This doesn’t affect all cameras but it does seem to be the case for some. That means that the exposure needed in lessons 2, 3 and 4 may be slightly higher than suggested in the lessons. You might use the “expose to the right” method.

Next Lesson: High Key