Aperture Paradox

Question:  If “fast” lenses are better, why are so many images taken in the “normal” aperture range?
Answer: The big advantage of “fast” lenses ( and the reason they are called fast), is that they have wide maximum apertures, and so make faster shutter speeds available in low light, without having to bump up your ISO too far.  Another advantage is that wider apertures enable a tighter depth of field, and this is often used to blur the background (or foreground) in portraiture and still life photography.  Even so, for general shots, you’ll typically use an aperture of around F/8.  This is usually the “sweet spot” of a lens, at which it delivers optimum image quality.  Similarly, in many situations you may not want to minimize depth of field – when you want to get both eyes sharp in a portrait of someone sitting three-quarters on, for example.
Marg Jackman