Sports And Action Photography Tip Number 6....Fixed Aperture lenses work best for action sports photography
Tip #28) Buy Lenses With A Fixed Aperture If You Can Afford To.... Most cheaper lenses don't have fixed apertures, so when you set the aperture value to the smallest number like F3.8 with the lens at the widest zoom position, when you zoom out to the telephoto position, the aperture value will go up to like F5.6 and reduce the light into your camera.
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Many times this causes problems because if you don't have much light, your shutter speed might be too slow causing blur in your photos. More expensive lenses have fixed aperture values like F2.8, so when you zoom it stays at F2.8, unless you change it.
Most lenses that professional sports photographers use have fixed aperture values like F2.8, so they let in the most amount of light and can keep the shutter speed high to stop the action.