All Imagons were originally sold with three different diffusion discs matched to its focal length. The Imagon equivalent to aperture size is determined by the interplay between the imagon lens central opening and the modifiable arrangement of smaller openings on the diffusion disc. These taken together produce an "H-stop" designation which approximates the corresponding f-stop of a normal lens. By rotating the outer rim of the disc, the opening of these smaller holes can be modified, and by this the amount of softness, which superimposes the sharper core of the image, is also changed. Wider H-stops, or more-open holes, mean more softness.
