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This chapter is from the book

Choosing the Right ISO

If you're not worrying about how much of the picture's in focus, you can use Auto ISO or ISO 200 on a sunny day and you'll usually get sharp photos. However, there are situations, even outdoors, where changing to a higher or lower ISO makes sense.

When to Use a Higher (Faster) ISO

With a higher (faster) ISO, you can use narrower apertures or faster shutter speeds and still have enough light to shoot by, even with very long (10x or longer) zoom lenses.

If your camera cannot provide a hand-holdable shutter speed when you use Aperture Priority and select the aperture you want, you have a couple of choices: Increase the ISO to 400, or use a tripod.

If you are shooting with long lenses (8x or longer; 200mm or longer on most DSLRs; 100mm or longer on Olympus DSLRs), the issue of hand-holdable shutter speeds becomes even more critical: High zoom ratios not only bring distant subjects closer but also magnify every hand tremor. If you find that Auto ISO doesn't let you use a fast enough shutter speed to hand-hold your long zoom shots, use a higher ISO (400 or greater), enable image stabilization (IS/VR), or use a monopod or tripod.

Using ISO 400 or higher on cloudy days, around dawn, or around dusk also enables you to avoid camera shake, no matter what shooting mode you're using.

When to Use a Lower (Slower) ISO

If you want to use selective focus techniques outdoors to emphasize your subject, or if you want to use panning to capture a feeling of speed, you might need to use lower ISOs on your camera than what Auto ISO might select when you shoot with 1x–4x zooms. By using a low ISO (ISO 64–200), you can use the limited depth of field created by wide apertures to control what's in focus, or use slower shutter speeds for creative effects (compare Figures 7.4 and 7.5).

Figure 7.4

Figure 7.4 At ISO 1600, the camera uses an action-stopping 1/320-second shutter speed.

Figure 7.5

Figure 7.5 At ISO 100, the camera uses 1/25-second shutter speed so you get the sensation of speed from a blurred background).

u2192.gif

To learn more about choosing ISO settings, see the section "Using ISO Adjustments" on page 122.

u2192.gif

To learn more about IS/VR technology, see the section "Using Anti-Shake Technologies" on page 196.

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