If fractions and f-stops aren't your thing, don't worry. Regardless of the focal length of the lens you're using, you now know that by changing the f-stop, you're altering the volume of light that passes through the lens. If you have a 100mm lens with the f-stop set to f/4, the size of the aperture would be 25mm. By doing a bit of math, you can calculate the aperture size for a particular focal length. And zoom lenses (such as a 70-200mm lens) let you twist the lens to move through a range of focal lengths.įocal length is always measured in millimeters and often printed on the lens or camera body. A telephoto lens, for example, a 500mm lens, has a much longer focal length and a narrower field of view. A wide angle lens - for instance, a 24mm lens - has a very broad field of view and is often used for landscape photography. Focal length determines field of view, which varies from lens to lens. Manufacturers calculate f-stop numbers for a particular lens by dividing its focal length by the aperture's diameter.
The system is a bit counterintuitive, though, because smaller numbers indicate a larger aperture and larger numbers correspond to smaller openings. F-stop numbers are fractions that tell you the exact diameter of the aperture at a given f-stop setting. Each of these numbers correlates to a specific lens aperture size, or f-stop. If you've ever examined camera specifications, you've undoubtedly seen alphanumeric symbols like f/1.4, f/5.6 and f/22. Different lenses have their own range of aperture settings.
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