Alright ladies (and gentlemen!) — today we are bringing it all together.
Remember this? The triangle is our friend…
If you look through your camera eyepiece, you will see a little bar that looks something like this…
Yes, this one on the top of your camera works too… but when you look through your eyepiece, you’ll see the same meter at the bottom of your picture… that’s the one you want to use, because you want the correct exposure as you are framing your shot.
What you want to do, is set your settings to that the little ticker lines up in the middle. When it lines up in the middle, the image is correctly exposed. If the ticker goes to the left side of the middle, it is UNDERexposed (needs more light). The -1 and -2 are “stops,” so if your ticker lines up under the -1, that tells you that the image is one stop underexposed. If the ticker goes to the right of the middle, it is OVERexposed (too much light).
So, back to the exposure triangle. First, we are going to set your ISO.
Assess the amount of light in the situation you are trying to photograph. If you are outside in bright sunlight, set the ISO to 100. If it’s cloudy or you’re in the shade, you might want to go with something from 200-400. If you’re inside a room, but with plenty of ambient light 400-500 might work well. If there’s not a lot of light, you may want to go with something higher – 1000 or more.
Once you have your ISO set, the next thing you want to do is decide what kind of image you are going for. Using your knowledge of aperture and shutter speed, decide what is most important and set that next. For example. If you are wanting to take an image of an ornament on a Christmas tree with lights nice and blurred in the background, the most important thing is to have a wide aperture, so you want to set your aperture to the smallest number possible (which will depend on your lens), but at something like 2.0. Once you have your aperture set, then you will look at your exposure meter in the camera, and adjust your shutter speed until the ticker lines up in the middle of the meter.
On the other hand, it may be more important for you to set your shutter speed first. Say for example, you are taking a picture of fireworks, and you want the shutter to stay open long enough to catch some nice movement in the streaks of the fireworks. You would set up your tripod, and set your shutter to something slow like 1/30 or even slower, and then adjust your aperture until the ticker lined up for a correct exposure.
Aperture f-stops are as follows: f/1.4, f/2, f/2.8, f/4, f/5.6, f/8, f/11, f/16, f/22, f/32. Each f-stop number lets in half as much light as the number before it. Some cameras will have other f-stop numbers to select, but they do not change a full stop.
Standard shutter speeds are as follows: 1/1000 s, 1/500 s, 1/250 s, 1/125 s, 1/60 s, 1/30 s, 1/15 s, 1/8 s, 1/4 s, 1/2 s, 1 s. Each of these shutter speeds lets in twice as much light as the number before it. So, adjusting from one to the other will make a full stop as well.
You can change the exposure by changing either the ISO, the shutter speed, or the aperture. If you have a correct exposure, and want to adjust one of your settings, you must also adjust another of the settings in order to go back to “correct”. For example, say my correct exposure was ISO 200, shutter speed 1/30 of a second, with an f-stop of f/5.6…. but you know that a shutter speed of 1/30 may give you a little blur in your image because of camera shake if the camera is not on a tripod, so you want to change the shutter speed to something faster. Leaving the ISO at 200, you can change the shutter speed to 1/60, which is down one stop (less light). So, in order to bring the overall exposure back to center, we must also move the aperture up a stop (more light) to f/4. Or, if you didn’t want to change the aperture, your other option is to go to 1/60, stay with f5.6, but then change the ISO to 400. (Doubling the film speed number doubles the amount of sensitivity to light).
Here’s another way to look at the triangle:
Hopefully that helps you understand a exposure. If you have questions, please post them in the comments section and I will do my best to answer them! Also, the book Understanding Exposure by Bryan Peterson is an excellent resource in… wait for it… understanding exposure.
Also if you have any photography questions that you’d like to be answered in an upcoming Photography 101 post, just shoot me an email at firstname.lastname@example.org.