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Arriving at the best exposure for a photo is part science and part art. In Foundations of Photography: Exposure, Ben Long helps photographers expand their artistic options by giving them a deep understanding of shutter speed, aperture, ISO, and all other critical exposure practices. This course covers the basic exposure controls provided by all digital SLR cameras, as well as most advanced point-and-shoot models. Learn how to master a camera's metering modes, how to use exposure compensation and bracketing, and much more. By the end of the course, you'll know how to develop an "exposure strategy" that will allow you to effectively employ your exposure knowledge in any shooting situation.
Even if you've only dabbled in photography, you've probably heard the term f-stop, or simply stop. Stop is a term that comes up regularly in photography, especially when you start working with your aperture control, the settings of which are regularly referred to as f-stops. But to a photographer, a stop is more than just a setting on your camera. It's a measure of light. Take a look at this. We've rebuilt the antique projector scene that we had earlier. What I've got here is the projector on a stool, and right now it's being lit just by this light right here, this one.
I'm going to turn on this light, which is going to double the amount of light in the scene. When that happens, we say that light in the scene has increased by one stop. Anytime you double or half the amount of light in a scene, you increase or decrease the light by one stop. It's really all there is. It's that simple. As you get more experienced, you might learn to recognize light changes in terms of stops, but that's not necessary to be able to properly expose your scene, thanks to your camera's light meter.
We also use the term "stop" to refer to how much light is striking the image sensor. Now as you've learned, the amount of light that's strikes the image sensor is controlled by your shutter speed and aperture size. You've already seen this list of shutter speeds, but now I want you to take note of something; 250th, 500th, 1, 000th, each of these is a doubling. A stop represents a doubling or halving of light, so each one of these shutter speeds is a one-stop difference. It should be pretty intuitive. At 1/250th of a second, the shutter is open half as long as it was at 1/125th of a second, and so only half as much light reaches the sensor.
Let's take a look at a real-world example. I'm going to take a shot of this scene. Here is our shot. As you can see, the camera metered at 1/250th of a second. Now I have both lights turned on, so I'm going to come over here, and turn off this second light, just like I did before. That's going to cut the amount of light in the scene by half. Now, I'm going to go back and take another shot. Now look what happened. The camera metered at 1/125th of a second, which should make sense to you.
I cut the amount of light in the scene in half, and so to correct for that, my camera had to double the shutter speed. Now, these two pictures don't actually look any different, and that's good. They shouldn't look any different. That means my camera is doing what it's supposed to do. Remember, it's always trying to meter to get a good amount of light, an amount that's neither too brighten nor too dark. So when I cut the light, it compensated it by decreasing my shutter speed to allow for a longer exposure. We're going to be talking about stops throughout the rest of this course. You're going to encounter them when we talk about aperture, metering, and many other topics.
As long as you always remember that a stop always represents a doubling or halving of light, you'll be fine.
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