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The F number is a ratio, right?
So f/2.8 means that at a focal length of 50mm the aperture is 17.86mm wide, since 50 / 2.8 = 17.86 (rounded up), right?
So in order to get an aperture of f/2.8 at 50mm the aperture has to open wider than it would at, say, 18mm, right?
Soooooo.... If the aperture can open that wide, why restrict it at the wide end of the zoom? Why not allow the photographer to have even wider apertures at the wide end? I admit that it makes life easy when you know that the maximum aperture is the same, regardless of focal length but you'd think at least one lens manufacturer would make a fast zoom with variable aperture.
So f/2.8 means that at a focal length of 50mm the aperture is 17.86mm wide, since 50 / 2.8 = 17.86 (rounded up), right?
So in order to get an aperture of f/2.8 at 50mm the aperture has to open wider than it would at, say, 18mm, right?
Soooooo.... If the aperture can open that wide, why restrict it at the wide end of the zoom? Why not allow the photographer to have even wider apertures at the wide end? I admit that it makes life easy when you know that the maximum aperture is the same, regardless of focal length but you'd think at least one lens manufacturer would make a fast zoom with variable aperture.