Aperture seems to work in reverse to common sense. Measured in f/stops, the smaller the f/stop, the larger the aperture or opening of the camera’s iris and the more light is allowed to hit the sensor. It also controls the Depth of Field or how much or how little the plane of focus is in your photographs.

In the photo of Expedition EVEREST, I wanted everything sharply focused (a large plane of focus) from the tops of the trees to the clouds in the sky.

Expedition EVEREST in Disney’s Animal Kingdom.
Nikon D70/18-200VR, 1/60s, f/18, 200 ISO, +0.3 EV, 35mm Focal Length

To get the maximum depth of field, I moved the Dial Mode to the A position to put my camera in Aperture Priority mode. I now had control of the aperture or f/stop setting by turning the command dial (this may be different for your camera so check your manual. There I go again!). I took a series of photos of Expedition EVEREST, waiting for the train to enter the mountain. It took a few tries to get the timing down. Once I downloaded the files to my laptop, I liked this one the best at f/18. It shows every detail in mountain’s “rock” and “snow” with a nice base frame of trees and top frame of sky. I took this while waiting outside the Theater in the Wild to see Finding Nemo — The Musical.

On the Maharajah Jungle Trek, the sun angle on this hanging Malayan Flying Fox showed how thin the membranes are in his wings. To make sure the background went out of focus, I selected an aperture of f/5.6 for a narrow plane of focus. This technique is called selective focus and is a great way of separating your subject from a busy or unappealing background.

Malayan Flying Fox (Pteropus vampyrus) soaking up the sun on the Maharajah Jungle Trek.
Nikon D70/18-200VR, 1/25s, f/5.6, 200 ISO, +0.3 EV, 120mm Focal Length