Why is 70-300 VR so cheap?

Ignoring why this lens is relatively low priced, and also f5.6 lens AF speed is usually slower than f2.8 and f4 AF speed; f5.6 AF speed is almost always fast enough for subjects moving across the frame, and by f8/11 there is usually little difference in image quality compared to a lens costing 3-10 time more.

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Leonard Shepherd
Many problems turn out to be a lack of intimate knowledge of complex modern camera equipment.