If the lens show traces of hand grease or halos, they must be cleaned with liquid, but not before using the bellows and brush as above. In fact, if the grains of dust are not removed, before starting cleaning, it may cause scratches on the surface of the front lens. Then drop one or two drops of fluid (or other lens cleaning detergent) on the optical papers or cloth (never directly on the lens) and proceed with the cleaning, applying a light pressure, with spiral movements starting from the center of the optic towards the periphery.
Cleaner is the purest liquid used by Still Life Photographers for sensor cleaning, it contains less than 5 parts per million of contaminants (whitish residual present after evaporation), dries quickly and leaves no stain or residue after application. The properties of this liquid mean that it is not necessary to dry the lens after its application, as it evaporates very quickly.
