We've delved a bit into Shutter speed, so now, let's take a look at Aperture
A reminder from our Exposure Triangle entry:
Aperture, in photography refers to the size of the opening in the lens, through which light travels onto the camera sensor. The larger the hole, the more light passes to the camera sensor. Aperture also controls the depth of field. Depth of Field is the part of a photo that appears to be in focus. If the aperture is small (a big f-stop number), the depth of field is large, and most or all of the photo is in focus. If the aperture is large (small f-stop number), the depth of field is small. F-stop numbers are expressed as a focal ratio, since the f-stop number is the ratio of the diameter of the lens aperture to the length of the lens. Examples of f-numbers are: f/1.4, f/2.8, f/4.0, f/5.6, f/8.0, f/16, f/32. Remember, this is a ratio, so a tip is: big numbers mean big focus depth (f/16 or f/32) and small numbers mean small focus area (f1.4 or f/2.8).
Moving from all Auto on your DSLR, to Aperture priority mode on your DSLR is one of the first steps that most photographers make when trying to understand their camera. It helps you take control and to get better. Congratulations, you are now on your way to learning your craft!
Of course, one of the challenges is now to understand all the settings and acronyms. Aperture Priority (A on the mode dial for Nikon, Av for Canon) is where you control the Aperture, or size of the lens opening, and let the camera guess at all the other settings. The hardest part about Aperture is remembering, Low numbers means Bigger opening (We're dealing with math and a ratio of opening size to lens length. Ughh! Math...)
Most people use Aperture setting if they want to control most of the picture outcome, but need to do so in a fast paced environment. With your thumb on the wheel, you can quickly dial the Aperture open or closed, and make the shot.
Depth Of Field Focus
Aperture allows you to control the Depth Of Field in your photos. If you want to make photos of say, a beautiful landscape, then, you want a larger Aperture number (f/16 or f/32) to allow you to get more of the Picture in focus. If you are shooting a person, say, perhaps from the waist up, and want to slightly blur the background, and make the subject the only focus, you would close down the Aperture, to perhaps f/5.6 or f/4. If you are shooting really close, macro photos, perhaps you want one leaf in focus, or one petal of a flower, then, you make your Aperture really small, at f/1.4 or f/2.0.
Aperture can help you capture motion, as well. By making your camera opening larger, it allows you to make the shutter speed faster to get a Freeze in Action. Aperture, Shutter Speed and ISO all work together to make the Photo!
In this photo of the girls, the Aperture is opened up to f/8, which allows the faster Shutter Speed of 1/250th of a second. We've caught, frozen, them as they step off the boat!
Shutter Speed Tutorial: http://www.bluefinstudios.com/blog/2012/11/what-is-it-about-waterfalls