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From the author of Key #7—Use All the Light You Can

Key #7—Use All the Light You Can

One of the dirty little secrets of today’s digital cameras, both point-and-shoot and digital SLRs, is that the higher the zoom setting, the less light that enters the lens. How much less? A lot less.

For example, a typical 18-55mm (3x) zoom lens is marked 1:3.5-5.6, which means that the widest lens opening is f/3.5 at 18mm (widest angle) and gradually narrows to f/5.6 as you zoom to 55mm. At 55mm, the lens at maximum aperture permits only about 1/3 the light as at 18mm.

If you have just enough light to shoot at 18mm (wide angle), you will run out of light as you zoom. Here are some workarounds:

  • Increase the ISO to the next available setting, provided you can still shoot with adequate image quality.
  • Use your flash if your subject is within 15-feet. Use ISO 400 for flash, and make sure you reset your white balance to Auto or Daylight.
  • If you have a digital SLR camera (the type of camera that uses interchangeable lenses), buy a faster (wider-aperture) lens. I have a 50mm f/1.8 lens (available for about $100 or so from Canon) and an 17-50mm f/2.8 zoom (available for around $400 or more from third-party vendors) for my Canon Digital Rebel XTi; comparable lenses are also available for Nikon and other major brands.

How fast is the 50mm f/1.8 lens? Compared to f/3.5, f/1.8 allows 4x more light; compared to f/5.6, about 9x more light (see http://en.wikipedia.org/wiki/F-number#Typical_one-third-stop_f-number_scale). The 17-50 f/2.8 lens allows about 1.6x more light than f/3.5 and 4x more than f/5.6 at any zoom setting.

Add one of these lenses to your camera and you have some serious low-light photography power. Compare Figure 12 to Figure 8 to see what using a digital SLR camera with a fast lens can do for your low-light shooting.

Figure 12 A faster lens (f/2.8), a faster shutter speed, and a larger image sensor make for a usable ISO 1600 photo of a clown car.

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