Baader CCD Complete Filterset 36mm LRGBC, H-alpha 7nm, OIII 8.5nm, SII 8nm - 2mm thick
Without modern RGB-filters, the CCD-revolution in astronomy would never have happened. It´s these filters that allow schools and universities do do meaningful imaging in science and education under totally light polluted skies from the midst of major cities.
Unlike terrestrial objects, astronomical objects shine in discrete emission lines. For this reason, any RGB-filter design with gently raising and falling slopes on either side of the transmitted spectral region generally is undesirable. The stars themselves obey to the laws of physics and shine by their stellar temperature colour - with a smooth, wide spectrum. This richness of colours can be covered nicely when adding an L-filter into the imaging process. However - shades and colour hues such as in earthly objects are not available when imaging the sharply defined emission spectra of deep sky objects. For this reason the slopes on RGB filter curves ought to be produced extremely steep for each colour channel - for maximum energy collection efficiency, while maintaining maximum contrast between the individual spectral emission lines.
Peak transmission of Baader RGB filters are extremely high but at the same time encased tightly within each of the three colour channels - with a very important and deliberate overlap between the B and G spectral region and a calculated wide gap between G and R to exclude a whole family of undesirable terrestrial street light emission lines (just like a UHC nebula filter). Thus colour balance and colour rendition of Baader RGB filters are outstanding, while stray light and reflections are simultaneously reduced to an unprecedented level - causing our filter recipe to having received the worldwide "chinese honour" of being copied by various OEM-marketing companies under a wide variety of trade names. Still our copyists need to prove that they apply the same care onto every aspect of the production process. This also includes selection of highly homogeneous glass-substrates, precision polishing of each individual filter, most expensive evaporation rare earth materials - and a number of other proprietary ideas - to really achieve the same performance on the sky. Given our precision in filter workmanship, the above mentioned B/G overlap does cleanly separate the key emission lines of H-beta and O III but at the same time allows to double the energy in the O III line. Within the spectral region around 580 nm there is no significant celestial emission line, however a whole family of street lights (mostly Mercury and Sodium vapour lamps) emit their devastating energy within that region. Exactly this spectral area is almost completely suppressed by the Baader RGB filter design. All these design features result in substantially improved colour balance and above all, this design transmits the full extent of energy of these important deep sky emission lines better than any other filter recipe we have analysed. The increased contrast and absence of haze and blurriness is recognized repeatedly by experienced users. In this way Baader RGB filters play a major roll in eliminating light pollution when imaging from flawed, light polluted sites.
When comparing different filter offers, always demand to see the full extent of the spectral area were modern CCD-cameras are sensitive, that is - between 300 to 1150 nm at least. Many companies only present a cut-out of the full CCD-sensitive spectral area - mainly to hide off band transmission were their inexpensive design has gaps which causes unwanted light to leak onto the image and spoil the data.
Transmission characteristics of all Baader filters are carefully optimized to only transmit wanted light without off band transmission
Transmission curves of the Baader LRGBC Filter (Luminance, Red, Green, Blue, Clear) and transmission lines of the bands H-Beta, O III, H-alpha and S II
|TRANSMISSION RANGE||multiple bands (see spectral image)|
|FILTER THICKNESS (WITHOUT CELL)||2 mm|
|CWL (CENTRAL WAVELENGTH)||656,3 nm;502 nm;673 nm|
|AR-COATING||dielectrically coated, planeoptically polished|
|FILTER SIZE||36 mm|
|FILTER USAGE||CCD, Focusing/dust protection, H-alpha, Luminance, O-III, RGB, S-II|
|TYPE OF FILTER||Bandpass, Narrowband|
|SINGLE OR SET?||Filter-Set|