Category S1 / Stormy, foggy, poor weather, or extremely overcast ("flat light") days.

The S1 Category means that the lens is clear or bright, ideal for stormy, foggy, bad weather or extremely cloudy ("flat light") days.

Its VLT range is between 44% and 80%. It lets a lot of light pass through to your eyes so you can distinguish dark areas and irregularities in the terrain when the day is completely overcast and there is no sun.