Aperture

 

As I said earlier, the light travels through the lens to hit the sensor and the lens on your camera has blades inside which can open up wide or narrow. You can also think of it as a hole in your lens which can change its size. Since a bigger hole will let more light in, a bigger hole will give you brighter pictures compared to a smaller hole.

Aperture values are called f-stops and are measured in fractions. An aperture of 1/4, for example, is written as f/4. Therefor, f/4 is a bigger aperture than f/8. This is how the aperture blades look at different aperture values:

 

When you purchase a lens, it always states the maximum aperture the lens can operate on. The 18-55mm lens that comes with most cameras as a kit, usually has maximum aperture of 3.5 to 5.6. This means the maximum aperture value of the lens is 3.5 at 18mm and 5.6 at 55mm. There are constant aperture lenses which keep the same aperture throughout the zoom range of the lens. These lenses are generally more expensive. There are also lenses with very wide apertures, such as f/1.8 or f/1.4. These are mostly fixed focal length lenses which can not zoom at all, also known as prime lenses. 

While different lenses have different maximum apertures, all lenses have roughly the same minimum aperture. I believe they all go down to f/32 or somewhere close to it. But if a wider aperture gives you more light, why would you want to use your camera at a smaller aperture? Well, the other thing aperture controls is depth of field. Depth of field determines how much of a picture is in focus. A wide aperture will give you a shallow depth of field, whereas a small aperture will have a larger depth of field. To explain this better I did a little test for you guys, I took 3 batteries and placed them in front of each other and focused on the battery in the middle.

This first picture was taken at f/4:

Since I focused on the battery in the middle, the two batteries closest and furthest away from the camera are out of focus and blurry. That is because at f/4, the depth of field is shallow or small.

This second picture was taken at f/10:

You can clearly see that both the batteries that were out of focus before are much more in focus now.

 

And this last picture was taken at f/29:

I used my 18-55mm kit lens for this experiment and put my camera in Av (Aperture Value or Aperture Priority) mode. In Av mode you select the aperture you want and your camera selects the right shutter speed for you. 

I would recommend you guys go play with your camera in Av mode and see the results at different aperture values. And then put your camera in manual mode and see what happens when all you change is the aperture value and nothing else.

Next I will talk about shutter speed, which is very closely linked to aperture.