Hi all, Quick (I hope) newbie query regarding lens quality with regard to aperture. I understand what lens focal length will do to a picture. I understand what aperture does to a picture. What I'm interested in is what the difference is between an f1.4, 1.8 on image quality if the aperture were similar. eg if I had a 50mm f1.4 or f1.8 and shot them both at f2.8 or a 50mm f1.8 and f2 and shot them both at f8 Is it purely down to lens positioning and cost in a family of optics or longevity of mount (over time it just happens) ? eg Nikon have a 50mm f1.8 and a 50mm f2, why? Thanks in advance !