Optika Italy B-1000 Série Manuel D'instructions page 14

In order to avoid a blinding
light when switching from
DF to BF position, a neutral
density filter is attached to the
BF/DF selector. (Fig.32)
The neutral density filter can
also be detached from the BF/
DF selector by unscrewing the
fixing screw on the left side. In
this condition, you can pull the
ND filter out while using the
BF illumination. (Fig.33)
Page 14
Fig.32
Fig.33