There are times when you'll want your photographs to take a broad, panoramic view, and times when you'll want to tighten your field of vision to focus on a specific portion of the image. Bringing those details closer is the job of your camera's zoom function. Most digital cameras use both optical and digital zoom. They work differently, and understanding their differences is crucial to getting the best photos.
Your camera's optical zoom is determined by the physical distance between your lens and the imaging sensor. You can watch it happening by moving your zoom button, and watching the lens slide in and out. As the lens slides further out, it narrows the field of vision and focuses a smaller portion of your scene onto the imaging sensor. Since the smaller segment takes up your whole sensor, the effect is to magnify that section of your image. Optical zoom typically magnifies your image three to five times, so it's expressed as a 3X or 5X zoom.
Digital zoom works much the same way your photo-management software does, when you crop and enlarge your photos. When you hold down the zoom button, your camera automatically selects an ever-smaller section of the image and enlarges it, creating an effect similar to optical zoom. Like an enlarged photograph, the quality of your digitally zoomed image will decline as you zoom. The small sensors in point-and-shoot cameras have fewer pixels, so they'll deteriorate rapidly at high zoom rates. Good digital SLRs have much larger sensors, which record more image data and can support higher levels of digital zoom.
Using only optical zoom produces the best images, but is limited by the lens's maximum zoom rate. Some cameras, primarily digital SLRs, can use add-on zoom lenses to gain additional distance. Digital zoom magnifies the impact of optical zoom, so if your camera has 3X optical zoom and 10X digital, your maximum zoom is actually 30X. Some newer cameras offer "superzoom" capabilities of 15X to 50X or more, with specialized circuitry to tweak the images and maintain their quality. Fine-zoom features use similar technology to sharpen images at normal zooming levels. Cameras with a macro setting use digital and optical zoom to create detailed images of very small objects.
How you utilize your zoom capabilities depends on your skill level and intended use for the resulting photographs. If they're for digital use on your own computer or a website, quality is less critical and you can freely use your optical zoom or superzoom features. If you plan to print your photos, you'll need to be more zealous about image quality. Set your camera to use optical zoom only, whenever possible. If you regularly need digital zoom, choose a camera with a larger image sensor. That gives you a better "original" to work with. If you primarily print 4-by-6-inch images, "fine zoom" cameras optimize zoomed images for that print size.
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