"many" and "some" are not necessarily opposites at all. Technically, the numerical equivalency for each of these terms is just "one or more".
Typically, "many" is used to convey a sizeable proportion either where a) the exact proportion is unknown or b) where it is known to be less than a half yet still appreciable. "Few" typically conveys a quantity that is not sizeable or appreciable, and well under a half.
("most" technically establishes that the proportion is greater than a half. Typically, "most" is used to convey a very sizeable and appreciable proportion).
Common mistakes in interpretation are as follows: a) treating "many" and "some" as contrasts; b) assuming that "many" means a vast quantity; c) assuming that "some" means a paltry quantity.
Kaplan Teacher in Toronto