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You should already be comfortable with how shutter speed and apature effect your image when your shooting without a flash but when your shooting with a flash these two parameters take on very specific roles. Though I said that the flash is actually a continuous light the fact is that it's on for such a short period of time. But it's effectively instantaneous as far, as your camera is concerned. Let's take a super slow-motion look at what happens, when you press the shutter button to take a picture. Imagine that time has slowed down. Yes you may already feel that way from watching this movie but, let's just imagine that time has slowed down and that you are sitting inside a camera that is about to take a picture of me.
Now, this is a imaginary situation, a stylized representation here. Of course, if the camera was actually taking a picture of me I would need to be standing still and I'm moving all over the place. Just ignore that part. When the shutter button is pressed the shutter opens and begins gathering light. As more light strikes the sensor, the image gets brighter and brighter until finally the duration specified by our shutter speed is met and the shutter closes. So here's what our final image looks like. We were shooting at a thirtieth of a second and in this case that left us with an image that's a little dark but, we were afraid to go to a slower shutter speed because we didn't want to risk handheld shake.
We'd like the scene to be brighter. So let's shoot another. Let's shoot this scene again, but this time let's a use a flash. So, again the shutter opens, and now the sensor is gathering all this light around me. But now our flash fires. So, yes the flash has a duration but compared to the length of the shutter speed, its effectively instantaneous. So, finally we've hit our shutter speed, the shutter closes and here's our shot. Our shutter speed was the same for this shot and the camera and flash did a good job of calculating a flash exposure that left me well lit. It'd be nicer to have more light in the background though.
So lets do a third shot. Again the shutter opens and the sensor gathers light. And again, the flash fires. But the shutter is going to stay open for much longer this time. We have dialed in a 15th of a second this time. That's a full stop brigher than our last shot. This will give the camera more time to gather all this ambient light that's back here. So finally the shutter closes Leaving us with this image. With our longer exposure, the background was rendered brighter, while our camera, again, did a good job of calculating a nice amount of flash. So, this whole demonstration is just a complex way of saying, when you're shooting with flash, shutter speed has no impact on how bright the flash will be in your image.
Zero. While working with the flash, shutter speed controls the brightness of the ambient light in your scene. By altering shutter speed I can make the ambient light brighter or darker. In the last movie you saw how we can independently alter the ambient light and the light from our additional light source. As you've just seen, shutter speed is how you make an adjustment to the ambient light in your scene. So how do you change the brightness of the flash? You have four different mechanisms for changing flash brightness. You can dial the brightness of the flash up and down using controls on the flash.
These controls will actually add more or less light to your scene. You can move the flash closer or farther from your scene. As the flash gets closer, its impact will increase, as you'll see later, a little change in flash distance can make a big difference in the amount of light that's added to your scene. You can also change your aperture setting. In a flash picture, aperture controls depth of field, just as it does in a non flash picture, but it also controls overall brightness of the flash. As the aperture's stopped down the flash will contribute less light to your scene, also as the aperture changes the effective of range of your flash will change.
Finally you can alter flash by changing ISO on your camera. As ISO increases, so will the effective brightness of the flash. This is a lot of information, but these points are critical to your effective use of flash so I'll say it one more time. In a flash picture, shutter speed controls the brightness of the ambient light in your scene while aperture alters the brightness of the flash. You also have three other ways of altering flash brightness, flash position, ISO and flash power. For the rest of this course, we are going to do nothing more than manipulate these parameters to get combinations of flash and ambient light that we like.
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