Aperture : F-stop

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Aperture refers to the opening of the lens where light passes through to the camera sensor.

Aperture is measured in “f-stops”. You’ll notice numbers like f/1.4, f/1.8, f/2.0, f/2.8, f/4.0….f/16, f/22 etc.

The lower the f-stop number the larger the aperture. A larger opening for more light to travel into the camera. And the higher the f-stop number the smaller the aperture, a smaller opening for light to travel through.

In photos, this translates into, large aperture (low number) allows only a small part of the photo in focus and rest of it blurred or out of focus. Small aperture (high number) allows almost everything in focus.

Depth of Field

Then there’s this thing called depth of field (DOF).
Depth of field is the amount of distance in your scene that is in focus. To even confuse you more, large apertures (low f-stop numbers), give you shallow depth of field (short distance in focus, less scene in focus). And small apertures (high f-stop numbers) give you wide depth of field (large distance in focus, more scene in focus).

DOF-photography-tips

So, if you took a picture of a person at f/2.0 (low f-stop number = large aperture = shallow depth of field), the tree that’s standing 10 feet behind the person will be out of focus and blurred. But, if you took the same photo at f/22 (high f-stop number = small aperture = wide depth of field), the person, tree and any objects surrounding the person will all be in focus.

Here’s an example of photos taken at different apertures.

Aperture and Depth of Field

Notice how as the f-stop number increases, the depth of field increases, resulting in the more of the background in to focus.

As mentioned earlier, large aperture (low number) allows only a small part of the photo in focus and rest of it blurred or out of focus. Small aperture (high number) allows almost everything in focus.

Also think of it this way:

Small aperture number allows a small part of the image to be in focus. And large aperture number allows a large part of the image to be in focus.

When taking pictures of landscapes, high f-stop numbers like f/11, f/16 or f/22 are often used to achieve long depth of field to bring the majority of the scene into focus.

For portraits, small aperture numbers are often used to achieve shallow depth of field in order to isolate the subject by keeping the subject in focus and the background out of focus. As you see above, at f/2.0, the flowers behind the firetruck are blurry, and out of focus.

More Light

As I said in the beginning, the lower the f-stop number the larger/wider the aperture, a larger opening for more light to travel into the camera. And the higher the f-stop number the smaller the aperture, a smaller opening for light to travel through.

A wide aperture means the inside of the lens opens wider to let more light in to capture photos. This gives you the ability to take pictures even in low light situations without a flash. Once you learn the basics of exposure and the relationship of aperture, shutter speed and ISO properly, this will give you the ability to take less shaky and blurry photos. Why? Because the number one reason your photos are shaky and blurry are because your shutter speed is too slow. In auto mode, your camera will slow the shutter speed down in lowlight, if  your aperture won’t go any wider than f/3.5, f/4.0, or f/5.6(These are the typical starter lens’ widest aperture). It has to find a way to let more light in to capture a photo.

However, if you have a lens that has a wide aperture like, f/1.4, f/1.8 or f/2.0, you’re able to let enough light in the camera that way, and keep the shutter speed reasonably fast to avoid motion blur or camera shake.

Pretty much all lenses with wide apertures are on the expensive side. But for whatever reason, the 50mm f/1.8 lens is available for us all at just above $100. The outside of the lens is built with plastic, so it feels cheap but for me, the value is in the wide f/1.8 aperture.

Getting properly exposed photos require a balance between ISO, Shutter Speed and Aperture. All three of these elements affect each other. So, be sure to learn more about exposure from the following posts on Photography Tips Coner:

Shutter Speed
ISO
Exposure part 1
Exposure part 2


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5 Responses to Aperture : F-stop

  1. Jean-Pierre 05/01/2012 at 10:24 am #

    Just wanted to note that focal length and focal distance affect depth of field as well. I’m sure a lot of people will appreciate your photo basics breakdown!

    • Peter Bang 05/01/2012 at 11:07 am #

      Yup, true true. I briefly mentioned that in the post about “backgrounds”, but been debating whether to make DOF its own post. thoughts?

      • Jean-Pierre 05/01/2012 at 5:46 pm #

        I would say yes because some people don’t know that kind of stuff. A gentleman at a camera store couldn’t understand why his 12mm F2 on his Olympus camera still had so much DOF when taking photos of people outside. Lots of people follow your blog so it may be beneficial.

        • Peter Bang 05/02/2012 at 9:58 am #

          Good point. thanks for your input, Jean-Pierre.

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  1. UNDER EXPOSURE OF IMAGES IN-FRONT OF BRIGHT BACKGROUNDS | des-teeniz photography - 08/10/2017

    […] 3) Using a combination of both 1) and 2) while using a low f-stop number on your lens to create shallow depth of field and blur the background. 4) Using a combination of 1), 2), and 3) while shooting with a long focal […]

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