This O-III filter is designed for observing and photographing those gas nebulae in which doubly ionised oxygen fluoresces – i.e. primarily for planetary nebulae and supernova remnants. With a FWHM of only 9 nm and equipped with the CMOS-optimised coating technology, it darkens the sky background and thus also blocks stray light much better than its 10 nm predecessor. The narrower FWHM is not the most important improvement however – it is the significantly better blocking sides of the O III wavelength, as well as even steeper transmission slopes and a broad plateau in the transmission range. With a transmission of 97% for the emission line at 500.7 nm, practically all the light of the nebula passes through the filter. At the same time, this filter can be used photographically for practically any focal ratio from f/1.8 to f/12 without passing any light of the H-beta line. This makes the Super-G filter just as ideal for use in areas with high light pollution.
Super-G filter: The filter has the same thickness as the 1.25″/2″ Baader LRGB filters. In the transmission range of the normal green filter (490-580nm) there are no emission lines other than OIII; H-Beta at 486 nm is already covered by the RGB blue filter. So, when using the 9 nm O-III filter instead of the standard RGB green filter, emission nebulae are consequently emphasised much more strongly, while the stars appear fainter. This makes it suitable for use as a “super G filter”.
Photographic use: The 9 nm O-III filter can be excellently used photographically on all telescopes, especially with a DSLR or an astronomical OSC colour camera. It offers all the advantages of the CMOS-optimised Baader filters such as Reflex-Blocker™ coating against reflections, plano-optical polishing and age-resistant Life-Coat™ coating. For monochrome cameras, we recommend the even stronger Narrowband (6,5 nm) and Ultra-Narrowband (4 nm) filters , which are available specially adapted for different aperture ratios. For this comparatively broadband 9 nm filter, preshifting is not necessary at focal ratios faster than f/4, thus it can be used at all focal ratios.
The Baader O-III Super-G filter has got all the advantages of the new generation of CMOS-optimized Baader filters:
- Increased contrast, matched for typical CMOS quantum efficiency and s/n ratio
- Reflex-Blocker™ coatings, for largest ever freedom from halos, even under most adverse conditions concerning aux-optics
- Identical filter thickness to existing standards, with utmost care for parfocality
- Blackened edges all around, with filter-lead-side-indicator in the form of a telescope-sided black outer rim, to additionally eliminate any reflection due to light falling onto the edge of a filter, making additional front-masks obselete
- Each filter coated individually, with sealed coating edge (NOT cut out of a larger plate with coatings left exposed, read more)
- Life-Coat™: evermore hard coatings to enable a non-aging coating for life – even in a most adverse environment