Variable power optical system and imaging device

A variable power optical system comprising:

• a first lens group having a negative refractive power and a second lens group having a positive refractive power in order from an object side of the variable power optical system, wherein
• the first lens group has, in order from the object side, a negative lens whose convex surface is oriented toward the object side, a biconcave lens, and a positive lens, at least one of which is a plastic lens;
• the second lens group has, in order from the object side, a biconvex lens, a biconcave lens, and a positive lens, any two adjacent lenses of which are plastic lenses;
• in a direction from a wide angle side of the variable power optical system to a telephoto side of the variable power optical system, the first lens group monotonously moves from the object side toward an image plane side of the variable power optical system and the second lens group monotonously moves from the image plane side toward the object side;
• and,
• on condition that, when a sequence of respective plastic lenses in each of the lens groups is taken in order from the object side as the ith, fpi represents a focal length of each of the lenses;
• that fw represents focal lengths of the respective lenses achieved at a wide angle end of an entire system are taken;
• that fw/fpi represents a ratio between a refractive power of the entire system achieved at the wide angle end and a refractive power of each of the lenses achieved at the wide angle end;
• that P1 represents a total of fw/fpi pertaining to the plastic lenses of the first lens group;
• and that P2 represents a total of fw/fpi pertaining to the plastic lenses of the second lens group, conditional expressions (1) and (2) provided below are satisfied.
• −0.22<P1<−0.01 (1)
• −0.15<P2<−0.03 (2)