Understanding Aperture

The aperture of a camera is the opening in the lens that allows light to pass through. It functions much like your eye: when you’re outside in bright sun, your pupil is very small because there’s so much light. Then when you move into a dark room, your pupils dilate to allow more light into your eyes. The aperture of a camera works just the same. A bigger aperture allows more light to enter the camera, and a smaller aperture lets in less light.

For this image, I was shooting directly into the sun, so I had to “stop-down” my aperture (aka make it smaller) to f/8, to let in less light. Some people refer to apertures as f-stops. The f-stop is the number, like f/8 or f/2.

For this one, it was SO dark in the room, I had to have my aperture as wide as it would go, at f/2.8.

Blurry Backgrounds

Most people love the “blurry background” look that professional photographers achieve in their images, and this is controlled by the aperture. A bigger aperture has a smaller depth of field (or a smaller plane of focus); this means that fewer things in the image will be in focus. A smaller aperture results in a larger depth of field with more things in the image being in focus.

Check out this example. In the image on the left, you can pretty much see detail through the whole image. The tree in the back is relatively in focus, as well as all of the flowers in the foreground. As you move to the right, the background gets blurrier, and so do some of the flowers. In the far right image, only a few flowers are in focus, and the rest are blurry. This is a direct result of opening my aperture as wide as it can go.

The Tricky Part

The part where aperture gets a little tricky is with the numbers. A larger aperture actually has a smaller number associated with it. For example, a 1.2 aperture is one of the widest apertures you can have on a lens. An aperture of 22 is a very, very small aperture. This seems backward, however there’s a technical reason for it that we’re not going to get into. Just remember:

small number = big aperture = shallow depth of field = blurry background
—– —– —–
big number = small aperture = large depth of field = background in focus

Each lens has its own range of apertures available to it. Lenses are categorized first by the focal length of the lens, and second by the widest (or largest) aperture possible on the lens. Most kit lenses are 18-55mm, and have a maximum of 3.5-5.6 apertures depending on what focal length the lens is at. The problem with kit lenses is that an aperture of 3.5 or 5.6 isn’t wide enough to get the blurry backgrounds people usually want. For this, you’ll either want a fixed aperture zoom lens (meaning the max aperture is the same throughout the focal lengths) or a fixed focal length (non-zoom) lens. Fixed lenses, also called prime lenses, have the largest maximum apertures. For example, the Canon 50mm 1.2 has one of the widest apertures on the market.

The Takeaway?

If you want creamy, blurry backgrounds and you only have the kit lens that came with your camera, you’ll probably need to buy a new lens. My recommendations? If you’re on a budget (who isn’t?), definitely check out the Canon 50mm 1.8 lens (affiliate link). It’s the first lens I bought after I got my camera (read about that here), and it was the best purchase I could have made to help me understand apertures. If you have a bit more money to spend, I love the Canon 50mm 1.4 (better quality than the 1.8 lens) and the Canon 28mm 1.8, and if you really want a zoom lens, check out the Tamron 28-75mm 2.8 lens (affiliate links). Make sure if you are considering the Tamron that you get the correct mount type (Canon or Nikon) for your camera. The one linked is for the Canon mount.



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