1. An optical system comprising from an object side: a first lens having a negative optical power, including at least an aspherical surface and having a concave surface centered around an optical axis in vicinity of the optical axis on an image-side surface; and a lens group having a positive optical power, wherein the following conditions are satisfied, 
 10 mm< T ×sin θ<30 mm, 
 7 <T/f tot <20, where T: optical entire length of entire system (mm) θ: half angle of view f tot : focal distance of entire system (mm).