Shutter Speed, Aperture, and ISO form the three connected points of the photography triangle. These basic controls of your image are maintained in a delicate balance each time you take a photo. Each of these variables enable you to control the exposure of your image, the depth of field, help you keep fast-moving subjects from blurring, and let you take a photo with very little light available or work in direct sunlight. A mastery of these three variables -and their interaction with each other- can free you of the automatic settings (which are not that good) and produce truly professional images.
- Shutter Speed
The speed of the shutter is often expressed as an angle or a fraction. The speed determines how long light hits the sensor each time you expose an image. The longer the shutter is open, the more light will get in, the more the camera will see. A shutter speed of 1/60 means the shutter is open for 1/60th of a second. Not very long, but in daylight that might be too long depending on your aperture and ISO settings.
A high Shutter Speed (a smaller fraction) exposes the image for less time. It also reduces the chances for motion blur since the camera isn’t exposing the ‘real world’ for very long. In 1/6400th of a second, you can safely capture even a bird in flight while handholding the camera. If you do shoot at a lower Shutter Speed (a larger fraction) to let in more light, you should use a tripod to keep your camera steady or you’ll risk motion blur.
- Aperture (Iris)
The Aperture works much like a human iris, expanding and contracting to let in more or less light. Aperture is measured in F-stops, from f/1.4 all the way up to f/64. Going one f-stop, (like f/1.4 to f/2.0) means halving the amount of light the camera lets in. Aperture works differently than Shutter Speed, however, because the diameter of the iris effects your Depth of Field.
DOP (Depth of Field) determines what is in focus at what depth. The more you open up your iris (larger fractions), the shallower the depth of field. At f/1.0 someone’s eyes might be in focus but their ears and nose won’t. At f/22 or higher pretty much everything is in focus. Of course, the focal length of your lens also affects the DOP, are you using a wide-angle lens or a telephoto?
- ISO (ASA or Gain)
ISO stands for International Standards Organization. It’s not an acronym with any meaning for photography. Every camera has a set Exposure Latitude which is the range it can capture from darks to lights. The Latitude is usually measured in stops and while most cameras have ~6.5 stops, the human eye has 22 stops of Latitude! Adjusting your gain or ISO means moving your limited range up or down to properly expose your desired subject. The camera changes what it recognizes as the brightest and the darkest part of the frame.
Lowering your ISO (lower values) makes everything darker which is useful if your highlights are too bright. Raising your ISO (higher values) means darker things become brighter because you are shifting the latitude range down. At very high ISO’s (10,000 and up) you will see ‘noise’ in your shadows. This is because there’s not enough light in the shadows for your camera to pick up anything, but the dark areas are in the low-middle range of your latitude so they’re not considered “black”. The result is your sensor picks up random noise instead of a clear image.
To learn more about the triangle of photography or to get a professional to masterfully wield these variables for you, consider contacting us. Also consider further reading on Aperture, Shutter Speed, and ISO.
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