stop number vs focal ratio

stop number and focal ratio both are nouns.

Word	Noun	Adjective	Verb	Adverb
stop number	Yes	No	No	No
focal ratio	Yes	No	No	No

As nouns, stop number and focal ratio are synonyms defined as:

stop number and focal ratio: the ratio of the focal length to the diameter of a (camera) lens system

Other synonyms of stop number include f number, speed.

stop number (noun)	focal ratio (noun)
the ratio of the focal length to the diameter of a (camera) lens system	the ratio of the focal length to the diameter of a (camera) lens system