Thursday, August 4, 2011

Photography Basics, Part 2: Aperture

Part 1

Aperture

Usually found in the lens, aperture is an opening that allows light to pass through towards the shutter curtain. Aperture is adjustable in most cameras and helps regulate the exposure of the film or digital sensor.

The aperture also controls the depth of field of an image. Depth of field is the area of a photograph that is in focus. Using the camera's aperture, you can control the amount of the image that is in focus.

On older cameras, the aperture controls are typically found on the lens. On newer cameras, the controls are typically found within the menus or on the LCD display.

Aperture is expressed in "f-stops", most commonly f4, f5.6, f8, f11, f16 and f22. Some lenses or cameras have more f-stops and some have less. Some have intermediate f-stops, sometimes called "half-stops", which are found between the standard f-stops mentioned above.

By adjusting the f-stop, you either half or double the light allowed to enter the camera. For example, f4 allows twice the light as f5.6, while f11 allows half the light as f8.

On older cameras, a depth of field scale was given on the lens near the aperture controls. On newer equipment the scale has been omitted. Since the camera, lens, and format all play a factor, it would be impossible to make an accurate generic scale. However, someone has made a depth of field table that may be helpful.

Basically, the lower the number, the larger the opening, which allows more light to enter, and the smaller the depth of field. The larger the number, the smaller the opening, which allows less light to enter, and the larger the depth of field. For example, f5.6 has a smaller depth of field than f11, and f16 has a larger depth of field than f8.

Diffraction, something that is not often discussed, occurs generally at f11 and higher. At f11, the aperture opening is small enough that, while you've increased the depth of field, the image as a whole is less sharp. It's not usually noticeable without close study until at least f22. It's something to be aware of, but not anything to worry about.

The shapest aperture, while not the one with the largest depth of field, is usually f8. If you are photographing a single object and want it to be as sharp as possible, f8 is generally the best choice. (That is assuming that f8 gives you the appropriate depth of field for whatever you are photographing.)

Here are some examples of using a small depth of field:

Flower About To Bloom
Scottsdale, Arizona
I used f4 so just the top of the flower would be in sharp focus.
Thistle Flower
Cane Brake, California
In this image an f4.5 (an intermediate f-stop) aperture was used.
 
Flags, Riverside National Cemetary
Riverside, California
I used f6.3, which is an intermediate f-stop, between f5.6 and f8.

Dead Tree
Cajon Pass, California
Aperture f5.6 was used to draw attention away from the background.
Gears
Vulture Mine, Arizona
I used f5, an intermediate f-stop, for this photograph.

Aspen Tree In Autumn
Flagstaff, Arizona
I used f5.6 so the leaves and branches at the top of the tree would not be in focus.
Here are some examples of using a large depth of field:

Cathedral Rock At Red Rock Crossing
Sedona, Arizona
I used f18, an intermediate f-stop, to ensure the reflection and the distant rocks would be sharp.
Nevada Time
Hoover Dam, Nevada/Arizona
Using f16 ensured the forground and background would be sharp.
Arizona Hills
Quartzsite, Arizona
I used f16 for this photograph.
Riverside National Cemetary
Riverside, California
I used f16 for this image, as well.
California Highway 178
Inyokern, California
I used f18 to give me the appropriate depth of field.
High Tension Power At Mormon Rocks
Cajon Pass, California
I used f16 for this photograph.
Peaks And Ridges
Grand Canyon, Arizona
I used f16 for this image, too.
And here are some examples of using a middle aperture:

Headlight
Lake Isabella, California
Since there is little depth in this scene, I used f8 to ensure it would be as sharp as possible.
 
Ladder & Wall
Cane Brake, California
For this image, which was shaded, I used f7.1, the highest aperture I could get without using a tripod.
Drainage Pipe
Kernville, California
I used f9, an intermediate f-stop, for this photograph.
Wood Floor
Vulture Mine, Arizona
Again, shaded area, so I used f7.1, an intermediate aperture.
Ladder And Lamp
Vulture Mine, Arizona
I used f7.1 for this image, too.
The take away is low-numbered f-stops give you a smaller depth of field, high-numbered f-stops give you a larger depth of field, and mid-numbered f-stops give you the sharpest picture when there is little depth to the scene. With that knowledge, use the f-stop that gives you the effect you want for whatever it is you are photographing.

Up to this point you should know which shutter speed to use to capture motion (either blurred or sharp) and which aperture to use so the depth of field is the way you want it. Those are two important steps to making great photographs. Next time we'll talk about another peice of the puzzle: ISO.


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