ratios are maths way of say there are eg: 3 boys for 15 so there would be 18 people in the class
No. There is no platinum ratio.
No...
Applied to focusing lenses and mirrors, including telescopes, binoculars, and cameras, the focal ratio or 'F-number' is (the focal length of the lens or mirror) divided by (its aperture or diameter)
multiply by 2
80:30 is one possible answer.