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Old Jan 3, 2009, 4:16 AM   #11
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What does f4 and f2.8 relate too?:?

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Old Jan 3, 2009, 4:20 AM   #12
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This is the aperture of the lens. It controls how much light is let in. The term is a stop as it stops the light, and the difference between f2.8 and f4 is one stop so an f2.8 lens allows in twice as much light as an f4 lens. This will allow for a shutter speed twice as fast to be used in the same conditions with a f2.8 lens than with a f4 lens. For night games we all use f2.8 or faster, f4 is great for daytime shooting.

As you will have noticed f2.8 lenses are more expensive as they have to control the light a lot better to keep sharp. There is no f2.8 zoom that covers a similar range to the Sigma 100-300mm f4 that is as sharp.
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Old Jan 4, 2009, 12:23 AM   #13
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And just one added point, pordad (if I may put my half-cent worth in, Sarah, Mark and John)... as one goes to faster lenses with wider apertures - say, an f/4 to an f/2.8 - those lenses get larger and heavier. That's because they tend to have larger diameters with more glass - in order to allow more light in. So... don't be shocked when you see the size of a fixed-aperture f/2.8 lens at 300mm. Photography can be a workout in itself! The best of luck to you pordad and Happy New Year to everyone!
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