Aperture
Another factor to consider when looking at lenses is the aperture. The aperture is basically just the opening that allows light to hit you camera's sensor which, in turn, creates the image. You can compare the aperture to the iris in your eyes. The more open it is, the more light gets in. Now you will not see any aperture value on your lens or camera but instead you will see something called a f-stop. All you need to understand as you begin learning about photography is that the lower the f-stop, the bigger the aperture opening. You can use the picture below to see the relationship between the two.

If you set your aperture at f/2, your camera will be able to capture the image faster than it would if it was at f/8 since more light hits your sensor at f/2. If you want to learn more details about apertures and f-stops then you can go here.


The maximum aperture opening or lowest f-stop is clearly marked on camera lenses. It is the number found after the mark "1:". The reason for this is that not all lenses have the same maximum aperture but all can go to at least f/22 on the other end. Some lenses can only go up to f/3.5 while some can go to f/1.8. The lower the maximum aperture, the faster the lens is (again because it can open wider to let in more light).

It's an ongoing joke that the maximum aperture is stated on the lens because, the lower the f-stop, the more expensive the lens is. On some zoom lenses, you can see two maximum aperture numbers. Let's take the Canon lens 18-55mm 1:3.5-5.6. This means that the maximum aperture depends on what you set your focal length to. The first number, in this case 3.5, is the maximum aperture setting at the wide-angle side of the lens i.e. 18mm. The second number, 5.6, is the maximum at it's telephoto side i.e. 55mm. The difference due to the movement of the lenses when you're actually zooming in or out.