How Cameras Work Part 5: Aperture Priority

This is part 5 of a 6 part series on getting to know your digital camera. Read part 4: Setting Proper Modes on Your Camera.

In most cameras, the diameter of the image hole (aperture) is adjustable (either manually or automatically) with something called a diaphragm:

iris diaphragm

– a series of overlapping metal plates that can fold in on each other or expand out. Essentially, this mechanism works the same way as the iris in your eye — it opens or closes in a circle, to shrink or expand the diameter of the lens. When the lens is smaller, it captures less light, and when it is larger, it captures more light.

The plates in the iris diaphragm fold in on each other to shrink the aperture and expand out to make it wider. (Ref: HowStuffWorks.com)

Practical Tips

Let’s start out by setting the automatic exposure control to Av, Angel Mode (just kidding, it stands for “Aperture Priority” mode.) This allows you to choose an aperture setting, and the camera automatically sets the shutter speed. Shoot the same scene using a high f-stop (like f10) and then with a low f-stop (like f3.5). You may not see a difference on your camera?s viewing screen (its too small), but make a print and you?ll see that more of the scene is in focus when you shoot using a high f-stop.

As you can see in the image on the left, more of the background is in focus than in the image on the right. Which is correct? Well, beauty is in the eye of the gallery curator. But seriously, portraits of people are generally made with a low f-stop in order to blur any distracting background. In a cemetery, there are often many distracting monuments in the background. Unless you really want to see them all clearly, shoot your main subject with a low f-stop. This forces the viewer to focus (pun intended) on your subject!

Category: Cameras and Gear