The Sloan Digital Sky Survey (SDSS) filters were designed by
Fukugita et al. (Ast. J., 411/4, April 1996, p. 1748-1756) to include
five mostly non-overlapping filters covering 300 nm to the
sensitivity limit of silicon CCD cameras near 1100 nm. They combined
colored glass filters and short-pass dielectric coatings to steepen
the low wavelength side of the bandpass. The [O I] skyline at 557.7
nm occurs between the g' and r' filters, and is thus reduced.
UVBRI filters have been the standard for photometric measurements for
decades. They have evolved over time as technology changed. H.
Johnson in the 1950s and A.W.J. Cousins in the 1970s designed these
filters for photomultiplier tubes (PMT). M. Bessell in the early
1990s selected colored glasses to match the Johnson/Cousins designs
for CCD cameras of the time. However, Bessell's designs were based
upon colored glasses available at the time. Some of those glasses
(e.g. Schott KG-4 used in conjunction with Schott RG-9 to make the
"Is" photometric filter) have been discontinued. Lastly, PMTs of the
time limited light past 900 nm, whereas modern CCDs are sensitive to
nearly 1100 nm. Thus, to truly match the Johnson/Cousins Ic filter,
a dielectric coating must be used to block light past 900 nm for CCD
systems. This cannot be achieved with colored glasses. We use Ic and
Rc (c = Cousins) to designate that we match the Johnson/Cousins
designs with our coated filters, as closely as possible.
Astrodon Tru-Balance RGB filters have revolutionized CCD imaging.
Their popularity is due to ease-of-use, high optical throughput and
great resulting color for galaxies, star clusters and nebulae. There
are two varieties of Tru-Balance filters - E-Series and I-Series.
Astrodon Tru-Balance RGB filters have revolutionized CCD imaging.
Their popularity is due to ease-of-use, high optical throughput and
great resulting color for galaxies, star clusters and nebulae. There
are two varieties of Tru-Balance filters - E-Series and I-Series.
The Astronomik CLS is our inexpensive solution for the visual
deep-sky observation, b&w photography and CCD observation. The
Astronomik CLS filter is the right filter to gain the contrast of
nearly all objects under light-polluted skies with all sizes of
telescopes. Due to the design of the transmission curve the filter
reduces the sky background and gas nebulae planetary nebulae as well
as open clusters, globular clusters and galaxies are seen better. The
Astronomik CLS blocks the emission of Hg and Na streetlights as well
as all Skyglow-lines . All major emission lines from deep-sky objects
are passed without suppression. As you can see from the chart below
the most important part of the eye's night-sensitive region is passed
with maximum transmission.
The transmission curves of the Astronomik RGB filters are optimized
for the CCD-astronomy: With these filter-set, we finally can offer
filters that make color proof pictures of all objects possible.
Continuum radiators like stars and galaxies as well as objects that
shine only in single lines (e.g. planetary nebulae), are reproduced
in their true colors. Because of the design of the band pass of the
filters, the color sensitivity of the human eye is optimal
reproduced. You get CCD- pictures, that show the object optimal in
his colors, just as if you would see it, if your eye would be
sensitive enough.
These new filters serve particularly the needs of the digital
photographer imaging the solar system with electronic cameras or
Webcams (with IR-block filter removed) at long-focus telescopes.
