User`s guide

17
The u filter is made from 2 pieces of Schott colored glass. The first glass of UG11 defines the
red side of the pass band and the WG345 defines the blue side. The small amount of red leak
of the UG11 glass beyond 700 and 750 nm should not be a source of error except for very
red stars. The surface of the UG11 glass has poor resistance to weathering (humidity) and
must be protected in a manner similar to the vby filters. Unlike the interference filters which
cannot be restored, the weathered surface of this filter can be repolished. If a small amount
of weathering is observed, a white haze on the surface, a Q-tip with jewelers rouge and water
can normally repolish the surface. Use light pressure and blow dry the filter immediately
afterwards.
A paper entitled "A Short Tutorial on Strömgren Four-Color Photometry" by Dr. David
Crawford has been reprinted and is available free of charge. Contact Optec for details.