Entry level and amateur photographers learning their first DSLR camera are instantly confronted with the big three: ISO, aperture and shutter speed. And speaking from experience it can be terrifying. These three settings are the make or break functions to every photograph. While the combinations of the three are near infinite it does not mean it is impossible to gain a solid grasp on the concept of each as the learning progresses. With a base level understanding of ISO (film speed), Aperture (light), and the Shutter Speed (amount of time the shutter is open) photographic skills grow.
On any modern DSLR there is a setting either on the hard body or on the LED display that says "ISO". Under the ISO or to the side are numbers that range from 100 all the way up to 36000 (on higher end professional models). The ISO setting is the digital equivalent of using different film speeds in old 35mm cameras. Film speed, or ISO, is used to help achieve the proper light balance upon taking the shot. A great beginner tip for using ISO is the brighter the light the lower the ISO should be. For example, if you are shooting an indoor birthday party under low light, the ISO should be set at 400-600 (your mileage may vary). If shooting under intense sunlight the ISO is generally dropped to 100 (or even 50).
Very often during sunrise photography I leave the ISO at a flat 100 because I'm using a tripod. I generally try to keep it set to 100 in most situations. The higher the ISO the more noise you'll get on your photos. If you want a nice beginner e-book on improving your photos check out Trey Ratcliff's '10 Principal's of Beautiful Photography'.
This is a setting I didn't even know existed until I had to tackle photographing a kids birthday party. You can read that full post here. The bottom line is that you need to switch to Manual mode to take advanatage of shutter speed. You can do it other ways but Manual mode gives you total control.
Try to remember that shutter speeds double with every crank of the wheel. So you’ll usually have the options for the following shutter speeds – 1/500, 1/250, 1/125, 1/60, 1/30, 1/15, 1/8 etc. The idea of ‘doubling’ is useful because you're basically doubling the amount of light you let in each time you increase the shutter speed. So when you up the shutter speed you'll want to drop the f-stop to compensate for the new night.
To grab fast moving objects you'll want a faster shutter speed. This is definitely true when you're shooting kids, sports. etc.
In a nutshell, the Aperture controls the size of the opening for the digital sensor and it's more commonly called f-stop. The more open, the more light comes in. Aperture use controls the focus on the subject and background. A good rule of thumb to use is the lower the Aperture setting, the crisper the focal point will be but the less in focus the background will be. So f/2.8 will get a nice portrait with a blurry background. The opposite also holds true; the smaller the opening, the crisper the background becomes.
One simple tool to remember f-stop is to think about this: f/2.8 will probably only let you focus on 2 people while f22 will let you focus on 22 people. So imagine a large group shot of 22 people. It's a stupid little memory tool that helps me. I also learned a really dirty way of remembering this but there's no way I'll tell you unless I meet you for beers someday.
In many cameras, the F-stop are the same as Aperture, while in other DSLR cameras there is a dedicated F-Stop setting. F-Stop helps control the amount of light as well as the focal point in the camera. F-Stop, when used with the ISO, makes for tremendous range and artistic expression. As a good rule, especially with the DSLR cameras, adjust the F-stop in half-step increments and look at the photo taken to see the focus differences on the subject. When the desired setting is achieved, snap away and becomes the next Ansel Adams!