Sometimes it is desirable to make changes in exposure of fractions of a second, and this is not possible with a mechanical timer. A light integrator like the Metrolux, which controls exposure by measuring the total amount of light falling on the print represents the utmost in consistency. While on the subject of the enlarger, let's turn our attention to the lens. The films we will be using are much faster than enlarging paper, so exposure times are naturally shorter, and the light intensity will have to be reduced. Simply stopping down the lens to 22 or smaller is not the answer.
High quality enlarging lenses are sharper at wider apertures due to the effects of diffraction.
Start with the lens wide open and notice how crisp the edges of the grain appear. If you want to cut down the amount of light beyond this use a neutral density filter.