User`s guide

16
SECTION 7.0
STRÖMGREN FILTERS
The Strömgren uvby is the most widely used intermediate-band photometric system and is
often used instead of the Johnson UBV system. The letters u, v, b, y refer to the colors
ultraviolet, violet, blue and yellow respectively. Because these filters have a narrow passband,
the system is totally filter defined, and variations in detector spectral response, telescope
transmission, and the second order terms used for the extinction corrections and the
transformation equations can be safely ignored. In addition, the use of these filters provides
more useful astrophysical information than the Johnson UBV system.
The Strömgren filters offered by Optec are manufactured by Spectro-Film of Woburn,
Massachusetts to our specifications. Spectro-Film has been making the Strömgren filters for
professional observatories worldwide for the last 10 years and is considered a primary source
for these filters. When used with any CCD camera these filters will match the results from
most photometry programs throughout the world. Table 7-1 lists the optical specifications of
the Strömgren filters. Table 7-2 lists the physical specifications of the Optec Strömgren
filters.
OPTICAL SPECIFICATIONS
Center
Filter Wavelength Bandpass Type
u 342 nm 25 nm 6mm UG11 + 1mm WG345
v 410±2 nm 16±1.6 nm interference
b 470±2 nm 19±1.9 nm interference
y 550±2 nm 24±2.4 nm interference
Table 7-1. Optical specifications of the Strömgren filters.
The vby filters are multiple cavity interference type using dielectric quarter wave stacks with
spacers of metal film. They have excellent transmission characteristic and long life when
properly stored. However, all interference filters can be damaged when exposed to high
humidity for long periods of time. When not used, these filters should be stored in a glass jar
with a small amount of desiccant added to keep the air dry. In such an environment, these
filters will last virtually forever.
PHYSICAL SPECIFICATIONS
Diameter 12.7±0.15 mm
Thickness 7.0±0.3 mm
Surface Quality 80-50
Wedge Not to exceed 5 ARC minutes
Table 7-2. Physical specifications of the Strömgren filters.