Sunday, December 2, 2012

Understanding Aperture (F-Stops and Depth of Field)

After talking with a few different people recently, I realize that there are many amateur photographers out there that don't understand aperture. They don't really know what it is, how it works or what it does. If that's you, read below and I will explain it.
Dandelion Sunset - Stallion Springs, California
I used a large aperture to ensure a small depth of field and a sharp image. 
The aperture is a hole in the lens which allows light into the camera. This aperture (except on a few primitive cameras) is adjustable, measured in f-stops (or focal-ratio stops). With each f-stop, the hole either doubles or halves in size, allowing double or half the light to enter the camera. There are also intermediate f-stops, which fall in-between the full f-stops, on most modern lenses.
Man At Shoshone Point - Grand Canyon, Arizona
A small aperture was used so that both near and far in the image would be in focus.
Common f-stops are f2.8, f4, f5.6, f8, f11, f16 and f22. Intermediate f-stops can be half-stops, third-stops or quarter-stops, depending on the make and model. Many lenses do not have the full range of stops.
Pumpkin Painting - Stallion Springs, California
I wanted just a small portion of the image to be in focus, so I used a large aperture.
The larger the f-stop number, the smaller the opening and the less light reaches the camera. The smaller the f-stop number, the larger the opening and more light reaches the camera. For example, f5.6 lets in twice as much light as f8 and f8 lets in twice as much light as f11.
Destroyed By Fire - Victorville, California
A small aperture was used so that both the window frame (near) and the door (far) would be in focus.
The larger the aperture, the smaller the depth of field (amount of the scene in focus) will be in an image. The smaller the aperture, the larger the depth of field will be. For example, f2.8 will have a much smaller depth of field than f16. If you want one area of an image to be in focus and everything else blurry, use a large aperture like f4. If you want the entire image to be in focus, use a small aperture like f22.
Wheat Grass - Tehachapi, California
I wanted the background to be blurry, so I used a large aperture.
Diffraction is something that must be discussed here. With each lens and sensor or film, there is a point where an image will lose overall sharpness when the aperture is small. This typically begins around f8 and becomes easily noticeable around f16, although the exact f-stops will vary with each lens and camera.
Sunrise At Cadillac Ranch - Amarillo, Texas
I used a small aperture for a larger depth of field.
While you gain depth of field by making the aperture smaller, when diffraction sets in you will lose overall sharpness. A photograph where f5.6 was used will be sharper than a photograph where f22 was used, even though the second photograph has a larger depth of field. In other words, sharpness and depth of field are two totally different things. Lenses are at their sharpest when the aperture is large.
Old Life, New Life - Victorville, California
Notice that the leaves are in focus and the old house is out of focus. I used a large aperture for this image.
A good exercise is to place your camera on a tripod or flat surface and take a series of photographs of the same object, but with a different aperture for each image. What does the scene look like when f5.6 was used? What does it look like when f11 was used? When f22 was used? Pay attention to both depth of field (amount of the scene in focus) and sharpness.
Summer Mow - Tehachapi, California
I used a small aperture for a larger depth of field.
Knowing which f-stop to use can be difficult because there is no set answer. It will depend entirely on the scene, equipment and exactly what you want the image to look like. A good starting point is deciding what you want the depth of field to be and using the largest aperture that achieves that depth of field. This is where knowing your camera and lenses are important. The more you use your equipment, the more you'll understand exactly what you need to do to make the image look as you want it.
Shadow On Brick - Goodyear, Arizona
A large aperture was used for a small depth of field. Only the bricks at the very bottom of the image are in focus.
Some people believe that you can use a small depth of field to remove distractions from the background of images. While a shallow depth of field is a good tool to draw the viewer's eyes to a certain part of an image, that distracting background is still there--it's just a little less obvious. A distraction is a distraction whether it is in focus or not.
Fireworks Over Mission Bay - San Diego, California
For this photograph I used a small aperture so the entire scene would be in focus.
I hope this helps explain what aperture is and what it means for your images. It will take practice to fully understand it in a practical sense. Don't be afraid to take several photographs of the same object using different f-stops to see what works best for you and for the situation.

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