Digital Photography Aperture Tutorial
Apertures function the same in digital photography as in film photography. The aperture is the opening through which light can pass completely through your lens to the focal plane of your camera which holds your Charge Coupled Device (CCD) that captures a digital image. Aperture helps control exposure, depth of field, and the sharpness of your photos. Plus aperture can help you photograph in low light.
How is Aperture Notated?
Aperture numbers are notated as the denominator of a fraction, therefore the lower the number of aperture, the larger the hole. For instance f2.8 is twice as wide as f4.0. Each of these increments is referred to as a stop. Whole aperture stops from f1 to f22 are as follows: f1, f1.2, f2, f2.8, f4, f5.6, f8, f11, f16, f22.
Setting Aperture
On single lens reflex (SLR) cameras, or generally any camera without a fixed lens, there is a ring on the lens that allows you to select the aperture size. Typically, there are indicators for the different stops your lens supports.
For permanently mounted lenses, you may be able to set your aperture in one of the menus of your camera, or it may simply be automatically controlled with no option for manual control.
Exposure
The lower the aperture number, the wider the opening and the more light it lets in. Each whole aperture stop lets in twice as much light as the one before. For instance, f4 lets in twice as much light as f5.6.
Depth of Field
Depth of field is how much of the area in front and behind the subject that is in focus. Wider (smaller number) apertures produce a narrow depth of field, or total area that is in focus. Narrower apertures (higher numbers) give you a greater depth of field, allowing more area in front and behind your subject to be in focus. A good rule of thumb is that the aperture number tells you how many people you could get in focus at a time. For instance, at f2.8 you can get about three people in focus and at f8 you can get eight people in focus.
Overall Sharpness
Smaller apertures (higher numbers) use more of the center of the lens and less of the edge. The glass in the center of the lens generally produces the sharpest images. The smaller the aperture you use, the less of the edge you use. This will increase the overall sharpness of your images. A general rule of thumb is to shoot primarily not wider than within one or two stops of the widest aperture. For instance if you have an f2.8 lens, set the aperture to f4 or f5.6 to get sharper images.
Photographing in Low Light
In low light, a wider aperture lets you capture images at a faster shutter speed. Smaller apertures can give you more sharpness, so it is critical to find the right aperture/shutter speed combination for your particular photo. The great advantage of digital cameras over film is that you can experiment without wasting film and you can check your results instantly. Try different aperture and shutter speed combinations and see which works best.
