Theory and Practice of Photography

Aperture:

Aperture is the setting of the iris of the camera lens. Just as your pupils in your eyes expand and contract to let in more or less light, you can do the same with your camera by setting the Aperture.

The Aperture measurement is called F-stop. The higher the F-stop number, the smaller the iris is set in your camera.

The trade-off: Each concept of photography seems to have a trade-off that prevents you from wanting to use it all the time.

With Aperture the trade-off is called depth of field. In a perfect world, you would leave the iris open wide all the time so that you could let in as much light as possible. However, when the iris is open wide your focus distance is much shorter. This means if you are taking a picture of your family in front of the St. Louis Arch in the distance, your family may be in focus at a low F-stop, but everything in the background will be blurry.

Tricky Tip: Remember, the higher the number on your F-stop, the smaller the iris is and the less light will come in. This means that when you stop up, you are really making the iris smaller.

F-stop is usually measured in numbers starting with 2.8 and going up to 22. The longer the lens, the higher your lowest F-stop possible. This is because long lenses can't let in as much light.

Film Speed (ISO & ASA):

Film speed determines how sensitive your film (or digital camera sensor is to light). The higher your film speed, the less light you need to get a fully exposed picture.

This makes higher film speeds great for sports and low light conditions because the shutter and can be set faster at a lower F-stop.

The trade-off: If faster film speeds are more sensitive to light and capture fast action better, why not always use a high film speed?

The higher the film speed – the more grainy the photo is. Grain refers to the tiny dots of random colors that appear in a photo. Shooting with 400, 800 or 1600 speed film or sensor settings will often present pictures with confetti all over.

Shutter Speed:

Shutter speed is how fast the curtain in your camera opens and closes. The faster the curtain opens and closes – the more it stops the action and the crisper your in-focus pictures are.

Shutter speeds are measured in fractions of a second, such as 1/30 or 1/250 of a second.

The trade-off: If faster shutter stops action and gives crisper photos, why not always shoot with a fast shutter?

The answer here is that you are at the mercy of your camera. The faster the shutter, the less light can come in. Setting the shutter too fast will result in a dim or black frame. Too slow of a shutter will result in a washed out image.

Exposure:

Exposure can be defined a lot of ways, but basically it is the art of finding the balance between the above three terms.

A properly exposed picture will be taken at just the right F-stop to give perfect focus to your subject with just the right film speed to capture the action, yet not give too much grain, and the shutter speed will work with your F-stop to give the desired lighting and focus.

Metering:

Every camera on the market that takes a battery uses metering to some degree.

Metering is measuring the light to determine what other settings you need for your camera. With some cameras this happens without your knowledge, with more professional cameras it is something you see before you ever take a picture.

The trade-off:

The camera does its best to recommend the right F-stop, shutter speed and (in the case of digital), film speed. But sometimes the camera is tricked by strange lighting condition.

For example, if you are taking a close-up photo in daylight of a person wearing black or dark clothes – the camera may meter on the black clothes and open up too wide. This will result in great looking clothes, but everything else will be washed out. To trick the camera, it is best to meter on the area that you want best exposed.

To force your camera to meter on a given area – point the camera at the subject with the area you want metered in the center of the photo. Once you have focused and metered with the subject in the center (do this by holding your shutter button half way down), you can move your camera to compose the shot however you'd like – as long as you don't let go of the button.

Bracketing:

This is especially important if you are film photographer, but it works with digital as well.

Bracketing is used when you are unsure which settings will work best. Most cameras will do it automatically.

When you know your settings are basically right, set your camera to bracket (see your instruction manual). This will allow your camera to take either 3 or 5 pictures in a row, each with slightly different settings. The middle picture will be taken with the settings you or your camera think are right, the photos before and after will be taken with slightly lower or higher settings to adjust for exposure.