We are kicking off the Multi-Media blog with an overview of The Exposure Triangle, a principle of photography. There are three things that affect the amount of light that makes it to the camera’s digital sensor, or frame of film if you’re old school: aperture, shutter speed, and ISO. We’ll be going into more detail about each one of these in the weeks to come. For now, we’ll just briefly describe each one and how they relate to each other.
I found an excellent graphic depicting the Exposure Triangle on photographer Michael P. Young’s blog. I’ve posted it here, with his permission, for your viewing and learning pleasure.
The Exposure Triangle by Michael P. Young
The aperture is the opening through which the light passes on it’s way to the sensor. The aperture designation, measured in f-stops like f/2.8 or f/22, is inversely proportionate to the opening size, and the amount of light entering the camera. So, more simply, the smaller the number, like f/2.8, the wider the opening and the more light that reaches the sensor. A larger number, such as f/22, indicates a smaller opening and less light reaching the sensor. Aperture also affects the depth of field. A large opening (small value) gives you a shallow depth of field and anything that is not the same distance as the focus object will appear blurry. A small opening (large value) will pull the background and foreground more into focus.
Shutter speed is the amount of time that the sensor is exposed to the light. Longer exposures let in more light than shorter exposures. Faster shutter speeds are good for freezing movement and action. This is great for photographing sports, and hummingbirds (one of my favorites). Slower shutter speeds blur movement, so are not good to use when holding your camera by hand. But if you have a tripod or can set your camera on a still surface, like the ground, you can use a slower shutter speed. This is handy for blurring the water in a waterfall, or photographing in very low light conditions, like at night.
ISO is the sensitivity of the sensor to light. A smaller number, like 100, makes the sensor less sensitive to light, but captures a much clearer image. At a larger number, such as 3200 or 6400, the sensor is more sensitive to light, but the image will have more noise and be grainy.
Aperture, shutter speed, and ISO work together to determine the exposure of your photo. When set to auto, your camera decides the best values for the three settings based on current lighting conditions. But once you know what each means and how it affects the image, you can tweak the settings to fit your purpose. Here is a real life example that a friend of mine has problems with: the moon.
When you take a picture of the moon with your camera’s settings on auto, you end up with a black background and a blurry white spot. Overall, there isn’t much light available at night, so your camera automatically increases the exposure. The moon, however, is very bright in the night sky, so that part of your image is overexposed. To compensate for the brightness of the moon, you need to reduce the camera’s exposure. You can do this by changing any combination of the three components of the exposure triangle. I usually do this by trial and error. First, I increase the shutter speed, thereby decreasing the time that the sensor is exposed to the light, and take a photo. If the resulting image is still too bright, I can move the ISO down to 800 or 1600, and try again. If the moon in the picture is still too bright, I can increase the aperture value, thereby decreasing the size of the opening and the amount of light that gets to the sensor.
This photo was taken on my Pentax K-30 using a telephoto lens zoomed all the way in to 300 mm, with an aperture of f/5.6, a shutter speed of 1/6000th of a second, and an ISO of 1600.
I work very much by trial and error. I start with the camera on auto and look at the photo that results. Then decide how I want the image to be better: sharper, brighter, darker, less grainy, etc. And I try again. This is fine if you don’t mind experimenting and have the time. It is very bothersome if you are photographing something that isn’t permanent, like two toddlers playing nicely together. Conditions like these are very short lived so you have to make your best guess at the settings, or just go with auto.
Most of the time, when shooting under normal circumstances, auto settings will work just fine. Hopefully, you’ve learned a few things about the exposure triangle, and now, maybe, you’ll know how to tweak the camera’s settings on those occasions when you want a more unique photograph. Another great site for learning about all topics photographic is Digital Photography School. It’s where I go when I have questions…
Try This At Home
Take a picture of something moving pretty fast with your camera set to auto. See the motion blur in the image? See if you can take a clearer image by increasing the shutter speed. (Remember, increasing shutter speed will decrease your exposure. What are the two ways you can increase the exposure while keeping your faster shutter speed?) Post your before and after pictures on your blog, website, twitter, facebook, etc., and comment with a link! I’d love to see how you guys do. Be sure to include any questions you have in your comment!!
Does this clear things up a bit? Do you still have questions? Be sure to ask, I’ll be responding to all comments. We ♥LOVE♥ feedback!!
Be sure to check out the follow up articles on aperture, shutter speed, and ISO. Enjoy!