Controlling Light with Aperture

Aperture is the opening inside of your lens that regulates the amount of light allowed to pass through the lens and hit the sensor. The sensor records the image that your camera sees.

If you could see behind the glass in the front of your lens, you would see the blades of the iris that open and close. That's the aperture. The little opening on the left is about an f22 and the wide open opening on the right side of the image is about an f3.5.

Aperture is also known as an f/stop.

Grab your camera and put it into Aperture Priority Mode: A on most cameras, AV on Canon.

Explore the Apertures on your camera by turning selection wheel on your camera. Notice the number that is changing. That is the Aperture. You should be seeing numbers like this:

1.4 2 2.8 3.2 3.5 4 4.5 5.0 5.6 6.3 7.1 8 9 10 11 13 14 16 18 20 22

The numbers in Turquoise represent whole stops.

The numbers in Yellow, are the apertures available to help you "fine tune" your exposure by adding 1/3 more or less light. The yellow numbers are, can you guess.....1/3 stops!

This is an example of what full stops would look like from wide open to fully stopped down.

HANDS ON LEARNING: What does Aperture do?

We read above in the description of Aperture, that it controls the amount of light that is entering the camera, now let's grab our cameras and see it for ourselves.

Set the Mode Dial on your camera to M - manual mode
Zoom Out (wide angle)
Set the ISO to 1000 (yep, this is high, but your probably working indoors, so trust me on this)
Shutter Speed 1/10 (really slow, so rest your camera on table or tripod)
Focus on any subject and take a picture at the following apertures: 3.5 7 11 22
*Changing the aperture might require you to press an AV button in combination with turning a dial. Read your camera manual to see how to do this for your model.

Compare your images to the one's that I took. Your images should look similar:

My first image (top left) f3.5 is over exposed. That is because at the ISO and Shutter Speed combo, my lens let in too much light.

My second image (top right) looks better. At f7 the amount of light entering the lens works much better with my ISO and Shutter Speed.

The two images on the bottom, taken at f11 and f22 are both underexposed. Not enough light was allowed into the lens to create a good exposure with my ISO/Shutter Speed combo.

As I stopped down my aperture (made the aperture smaller) the image got darker.

So now you must be thinking, wow! Who knew. Uh, when would I use this bit of knowledge?
Well, when you need to set a shutter speed and leave it there to show motion in a photo or stop motion in a photo, you must adjust the aperture to let the proper amount of light in.