Consider the question. Lens speed refers to the maximum aperture diameter, or minimum f-number, of a photographic lens. A lens with a larger maximum aperture (that is, a smaller minimum f-number) is called a "fast lens" because it can achieve the same exposure with a faster shutter speed. Conversely, a smaller maximum aperture (larger minimum f-number) is "slow" because it delivers less light intensity and requires a slower (longer) shutter speed.

What does the speed of a lens mean?
 If the answer is 'the maximum aperture diameter , or minimum f - number , of a photographic lens'; explain the reasoning:
The relevant sentence in the passage is: Lens speed refers to the maximum aperture diameter, or minimum f-number, of a photographic lens.