An optical imaging system having a single focus includes a negative first lens group, an aperture stop, and a positive second lens group arranged in order from an object side. The first lens group includes a positive first front lens group including a positive single lens and a negative first rear lens group including a negative meniscus lens and at least one positive lens, arranged in order from the object side. The second lens group includes a positive second front lens group including a cemented lens of a negative lens and a positive lens and a positive second rear lens group including at least one positive lens, arranged in order from the object side. All of the lenses of the optical imaging system are spherical glass lenses.