Basics of Good Exposure, for Beginners in Photography

Regardless of whether or not you shoot film or digital, there are some basic rules and convention that you can use to help you get good exposure and to make better images.

Getting the right exposure can make the difference between a professional looking image and a mediocre one

A good exposure is based on 3 elements which you can control:

1. the ISO, which is the sensitivity of your film or sensor setting. Use low ISO (100-400) in daylight settings, use higher ISO for night time or lowlight situations. The higher your ISO, the noisier your image will look, so be mindful of how high you go.

2. The Aperture, represented by the f setting. This is literally how much light you are letting into the camera to your sensor. The aperture size is controlled by a dial on the lens for manual lenses or by software for most DSLRs. The lower the ISO (say 1.4, 1.8), the larger the opening and the more light gets to the sensor. Aperture also controls the depth of field (DOF). This directly affects how blurry your background appears, which is usually great for portraits. The lower the f setting (larger aperture opening), the more blurry the background will get. For landscape, use higher f settings (say f/16 or f/32) so more of your landscape features appear in focus.

3. The Shutter Speed. This is how long the shutter stays opens for, which affects how much light gets to the sensor. Shutter speed also affects how sharp or blurry an image may look. So for sports photography, you need to use faster shutter speeds to avoid blur, unless that is the effect you are going for. For night photography or taking still images of lakes or moving water, that blur is desired, so you need slower shutter speeds, sometimes up to a couple seconds. However, you would want to mount your camera on a tripod and use remote trigger to avoid shakes which will mess up your image. More on that below.

There is another element that you cannot ignore, which is the focal length of the lens you are shooting with. The focal length controls how wide or narrow the view will appear. So 24mm lenses are considered wide angle lenses on a full frame camera, whilst 50mm is considered standard, almost on par with the human eye's view. 80-150mm is good for portraits whilst 400mm or above is great for photographing wildlife. Typically, high focal length lenses have higher minimum f settings, implying that they let in less light. Most zoom lenses thus have a minimum f setting f/4.5 or more. In the world of prime lenses, the lower the minimum f settings of the lens, the more prized that lens is. Lower aperture lenses such as f/1.4 for full frame or f/1.9 for medium format are considered as "fast lenses". That term is used to imply that when using those lenses, you can have faster shutter speeds at low light settings, because more light gets to your sensor or film because of the low aperture setting.

To get good exposure, as a beginner, shoot in aperture priority mode. You set the aperture (depending on the look you are going for, taking note of your ISO setting) and the camera will automatically set the appropriate shutter speed to match. You can also use the shutter priority mode and the camera will set the corresponding aperture for you. Only shoot manual if your camera has an assisted manual mode, or you are adept with using an external light meter or the Sunny 16 Rule.

External light meters come in various forms

Some extra tips:

Using a tripod and a remote shutter release in low lit situations can greatly improve the sharpness of your image

1. Shoot with a tripod in low light settings. Standard convention is that at a shutter speed slower than 1/30 sec, you should not shoot hand held, to prevent blur and a soft image. Also, use a remote trigger with a tripod in low light situations to decrease blur and improve the sharpness of your images.

2. Make sure that at any given time, your shutter speed is faster than the inverse of the focal length of the lens you are shooting with. Otherwise, you will notice distinct blur or softness in your image. Thus for a 300mm zoom lens, shutter speed should be faster than 1/300 sec. Exposure should not be compromised, however. Just adjust your ISO or aperture to ensure that the shutter speed obeys that convention.

3. Use the Mirror Lock feature if you camera has it. Some SLRs have the ability to lock the mirror after composing your image. This prevents the shake cause by the mirror slap during shooting, as this motion of the mirror causes vibrations which can lead to blur and softness in the image, especially in low-lit conditions.

4. Be mindful of backlights. Backlit situations do not follow the normal conventions described above. It is always better to avoid backlights if you can help it. Never shoot with the sun behind your image, unless you are looking for that silhouette effect. It is never a good idea to fight the sun, you cannot win! I usually change my position to position the sun in front of my subject or to the side. In situations where you cannot lose the backlight, use the Auto Exposure Lock button to expose for the shadows. If your camera does not have this feature, try the general convention of overexposing your image by about 1.5 stops.

5. Have fun!