Simply put - Baader's new LRGBC anti-reflection filters deliver
improved color separation and image quality without annoying halos.
Unfortunately, their obvious improvements will likely cause many
astro-imagers to re-take images of their favorite objects...
What
makes the Baader filters so unique? Through an extensive coating stack
design and testing program, Baader has partnered with the world's
leading thin film coating company to produce transmission curves that
border on the ideal. Their ultra steep cutoffs and high transmission
(>95%) allowed Baader to do something to a degree no other RGB
filter set can manage - they are able to effectively separate the
important H-Beta and O-III lines. The Baader Blue filter passes
virtually all of the H-Beta and O-III lines, while the Green filter is
able to capture all of the O-III line, without encroaching into the
H-Beta line. None of the light is wasted by either filter. In this way,
O-III is represented as it should be, a teal (blue-green) color, and
H-Beta is captured solely in the blue. Never before has this degree of
separation been achieved, and with such high transmission of both
lines.
In addition, the Green and Red filter passbands nearly
touch, leaving only a sharp notch to block out the primary
Mercury/Sodium light pollution line at 580nm. The high transmission
everywhere else delivers the shortest combined exposures possible with
every detector.
In addition to their special transmission
properties, the Baader coatings were developed from the outset with
another key goal in mind - eliminate the annoying reflections present
in other astro-filters. To achieve this freedom from reflections
required careful balancing of the coating stacks and further extensive
testing. The result can be seen in these two images, showing the
freedom from reflections in the L and C Filters
The high
optical quality of the Baader narrowband filters guarantees no loss in
sharpness or contrast. Each substrate is fine-optically polished plane
parallel to deliver a smooth and accurate 1/4 wavefront over the entire
surface. Each filter is blocked and polished individually, not cut out
of a larger plate of glass. The special custom polishing operation sets
Baader filters apart from the lower optical quality provided by
standard commercially precision polished filter substrates used by most
other filter manufacturers.
Coatings are professionally
applied in Germany by the most sophisticated equipment available today,
ensuring high consistency for bandpass cutoffs, transmission, and out
of band blocking. The anti-reflection coatings are evenly balanced on
both sides of the filters to reduce surface stresses and prevent
deformation of the substrates. The ultra-hard ionbeam deposition
ensures the coatings will never degrade from use or normal cleaning.
Unlike many competitive filters, Baader coats each filter individually.
Baader filters remain sealed at their coating edges for a long life
without degradation (you can see evidence of this process by inspecting
for a thin un-coated region at the very edge of the filter). Though
more costly, this process avoids the coating failures that can result
when filters are simply 'biscuit cut' from bulk coated sheet glass,
leaving ragged coating edges for moisture to penetrate and cause
coatings to peel away from the glass. Baader filters are intended for a
lifetime of real-world use.
