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APERTURE, SHUTTER SPEED, ISO... Say, What?!?
Note: For these examples, all images were shot using a tripod and NO flash.
Shutter Speed vs. Aperture The first set of three shots show the effect that shutter speed has on aperture. As the shutter speed increases, the aperture has to open up to allow more light to achieve the same shot. All other settings remain constant. The trade-off is that you sacrifice focus for speed. Lens used was the Canon 100mm/f2.8 macro on a Digital Rebel XT... Click image to view 1000-pixel version in a new window; or CTRL+click for new tab.
	A slow shutter captures the flames over time, resulting in a smooth, sugary effect. With the aperture at 22, all logs are in focus. Shutter 2 seconds Aperture 22 ISO 200
	Faster shutter yields more detail to the flame. Lower aperture number results in loss of focus on the background logs. Shutter 1/15 second Aperture 4.0 ISO 200
	Faster shutter again, more definition to the flame. With the aperture wide open, only the foreground logs are clearly in focus. The "depth of field" is very narrow at larger aperture. Shutter 1/30 second Aperture 2.8 ISO 200

Aperture vs. Shutter Speed The next three images show the effect that aperture changes have on shutter speed. As the aperture opens up, letting in more light, the shutter speed can be relatively faster. All other settings remain constant. Lens used is the Canon 50mm/f1.8 on a Digital Rebel XT. Click image for full out-of-camera JPG (500KB - 1MB)
	Aperture is wide open, letting in more light. Notice that only the glasses are in focus. The chair in the background is just a blur. Shutter speed 1/25 second Aperture 2.8 ISO 100
	By closing down the aperture (letting in less light), the shutter has to be slowed down accordingly. But the smaller aperture allows more of the image to be in focus. Shutter speed 0.8 second Aperture 11.0 ISO 100
	By closing down the aperture completely (f/22), the maximum focus is available throughout the image. The obvious impact is that the shutter has to be slowed WAY down. In this case, 2.5 seconds to achieve the same shot. Shutter speed 2.5 seconds Aperture 22 ISO 100

What about ISO? The lower the ISO setting, the cleaner the image. But the lower the ISO setting, the more light is required to get the shot. Therefore, when light is at a premium, you can raise the ISO to use a faster shutter or smaller aperture. Here's the same shot as above, changing the ISO as we go. Lens used is the Canon 50mm/f1.8 on a Digital Rebel XT Again, click the image for the full out-of-camera JPG.
	ISO 100 Shutter 1/4 second Aperture 8.0
	ISO 200 Shutter 1/6 second Aperture 8.0
	ISO 400 Shutter 1/13 second Aperture 8.0
	ISO 800 Shutter 1/25 second Aperture 8.0
	ISO 1600 Shutter 1/50 second Aperture 8.0
As always, there are trade-offs to consider. By increasing the ISO, you can use a faster shutter, but your images will have more "noise" (a grainier appearance), which is especially noticeable in the ISO 1600 shot.

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