Aperture, Simply Explained

12Dec10

When anybody first gets interested in photography, the first thing they always ask a seasoned photographer is, “hey, how do you get the background all blurry?”. Well, the answer is quite simple – use a high aperture.

The higher the aperture, the less depth of field you have. Using a medium telephoto (85 mm) to telephoto lens with a high aperture (such as f2.8) works best as telephoto lens compresses the image and high apertures put the majority of the photo out of focus.

Aperture basically controls the depth of field of a photo. If you are new to depth of field, its actually not a very difficult concept to grasp. Think of it this way, if you have a high aperture such as f1.4, your photo will probably be sharp for less than a foot. With the amazing auto focus that cameras have, you can select where that less than a foot is and your camera will render that area sharp and everything else blurry or out of focus. This is a great way to photograph people as their face is photographed sharp and everything around them (even their hair sometimes) is out of focus; This allows your viewer to focus on the person and ignore extraneous elements around them. If you have a very low aperture like f22, your camera will have just about everything from 3 feet to infinity in focus. Landscape photographers often use very low apertures to keep their entire photo sharp as a tack as they would like their viewers to see a stick on the ground 20 feet away and a bird in the sky 30 feet away in focus.

The bottom line is, aperture controls the in and out of focus elements of your photograph. The lower the aperture gets (represented by higher numbers) the more elements that are in focus in your photo. The higher the aperture is (represented by lower numbers), the less that is in focus. Of course, light also has an effect on all of this, but more on that in another blog post.

See some examples below of photos taken with different apertures. Click any of the photos to enlarge them and get a better view.

Triborough Bridge taken from Astoria, New York. Picture taken at f25 As you can see, there is a lot in focus in this picture. Basically everything, all the way to the Manhattan landscape. I was also using a tripod for this shot, which kept the camera steady due to the very low shutter speed of 1/6 second.

Crescent Street in Astoria, New York. Taken at f16. As you can see, almost everything from the street sign that says “Crescent St.” to the green car all the way in the background is pretty sharp. I could have used an even higher aperture, but you usually get what you need out of f16.

Me, Taken on New Years Eve about 4 years ago. This picture was taken at f2.8 and it is a really great example of how aperture works. The autofocus focused on the beer bottle in the front and stay in focus for about 1.5 feet before dropping off when it got to my face. As the depth of field went even further back to my hand, it got even more out of focus. Out of Focus is gradual, it doesn’t just go out of focus, it slowly gets more and more out of focus as depth of the photo increases.

My brother and his girlfriend in Ireland. This picture was taken at f4, which is still pretty shallow. As you can see, their faces are in focus, but the background is completely blurred. This was also taken on a telephoto lens, which helps the background blur a lot quicker than it could with a wider lens or normal lens.

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