We did this by shooting in the A or AV setting on the camera. (Yeah, I'll explain later). Using that setting, you control exactly what you want the aperture to be - within the limits of the lens - (Yeah, I'll explain later). Earlier, we learned that the aperture is just one of three forces that affect the exposure of the camera. When you shoot in A or AV, and set your own aperture, the camera measures available light and adjusts the SHUTTER and ISO to maintain a good exposure.
The reason this is important is the OTHER function of the aperture. We learned that the aperture also controls HOW MUCH light comes in. So, using the above apertures, with the shutter set at 1/6th of a second, and the ISO at 100, (Yeah, I'll explain later), I took two shots of a candle. The first, shot at f-1.8 is shown here.
Not a lot of light if the shutter is only open at 1/6th of a second, and the sensitivity is set at 100. But what happens if I let a lot less light in? For one thing, both candles would be in focus, but...
Sure it's in focus, but we can't see it. The moral of the story is that as we control the amount of focus, the light let in changes dramatically. If we want just our subject in focus, we let a lot of light in, forcing us to have a very fast shutter speed. And if we want the entire scene to be in focus, we need a ton of light, and a much longer shutter speed. The danger of that is that you can not hand hold a camera for that long, causing a blurry shot.
But that is for tomorrow.