<p>For the first time, the value of the geometric light-gathering power of the optical system was estimated and its effect on the spatial resolving power of the camera-like eyes of one species of gastropod and human was analyzed. In a mollusk, calculations are made for the diameter of the pupil, in humans – for the diameter of the pupil and for the diameter of the entrance pupil. It was shown that the value of the geometric light-gathering power of the optical system of the camera-like eye of a mollusk, calculated for the diameter of the pupil, is constant due to the constant diameter of pupil. The values of the geometric light-gathering power of the optical system of the camera-like eye of humans, calculated for the diameter of the pupil and for the diameter of the entrance pupil, are variable due to the variable diameter of the pupil and the diameter of the entrance pupil, respectively: both increase with increasing diameter of the pupils. The value of the geometric light-gathering power of the optical system of the camera-like eye of a mollusk, calculated for the diameter of the pupil, is greater than the value of the geometric light-gathering power of the optical system of the camera-like eye of a human, calculated for the diameter of the pupil. The geometric light-gathering power of the optical system does not affect the spatial resolving power of the camera-like eyes of mollusks and humans.</p>