Anyone Can Make A Picture.
But, making good photos is hard. You can snap hundreds, and hope things come out right, or, you delve a bit into understanding light and your camera settings, and make good photos.
Most DSLRs have “Auto” modes that automatically guess the right shutter speed, aperture and ISO for your shot. But, using Auto mode puts limits on what you can achieve. As I said, the camera has to guess what the right exposure should be by evaluating the light that comes into the lens.
Eliminate the guesswork. Understand how ISO, shutter speed and aperture work together to allow you to take charge of your photos. Once you can manually control your camera, you can be creative and dictate good and bad photos.
Bad news Alert! There's math involved! Kinda...
ISO is the amount of sensitivity of your camera to light. It is typically measured in numbers, with a lower number meaning lower sensitivity to available light, and higher numbers meaning more sensitivity. More sensitivity comes at the cost: more ISO means graininess or noise in the images. Examples of ISO: 100, 200, 400, 800, 1600, 3200, 6400, etc.
Shutter Speed the length of time the camera's shutter is open to allow light into the camera sensor. Shutter speeds are measured in fractions of a second, when they are under a second. Slow shutter speeds allow more light into the camera sensor and are used for low-light and night photography, while fast shutter speeds help to freeze motion. Really slow shutter speeds, like more than a second, are often called Long Exposure. Examples of shutter speeds: 1/15 (or 1/15th of a second), 1/30, 1/60, 1/125, 1/250, 1/400, 1/800 and so on. Long exposure examples: 1' (1 second) 2', 5', 30' or even more.
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).
More Tutorials on Settings:
Aperture Tutorial: http://www.bluefinstudios.com/blog/2012/11/tutorial---aperture-priority
Shutter Speed Tutorial: http://www.bluefinstudios.com/blog/2012/11/what-is-it-about-waterfalls